Patent Publication Number: US-2023164106-A1

Title: Generating Context-Aware Rendering of Media Contents for Assistant Systems

Description:
PRIORITY 
     This application is a continuation under 35 U.S.C. § 120 of U.S. patent application Ser. No. 17/136636, filed 29 Dec. 2020, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to databases and file management within network environments, and in particular relates to hardware and software for smart assistant systems. 
     BACKGROUND 
     An assistant system can provide information or services on behalf of a user based on a combination of user input, location awareness, and the ability to access information from a variety of online sources (such as weather conditions, traffic congestion, news, stock prices, user schedules, retail prices, etc.). The user input may include text (e.g., online chat), especially in an instant messaging application or other applications, voice, images, motion, or a combination of them. The assistant system may perform concierge-type services (e.g., making dinner reservations, purchasing event tickets, making travel arrangements) or provide information based on the user input. The assistant system may also perform management or data-handling tasks based on online information and events without user initiation or interaction. Examples of those tasks that may be performed by an assistant system may include schedule management (e.g., sending an alert to a dinner date that a user is running late due to traffic conditions, update schedules for both parties, and change the restaurant reservation time). The assistant system may be enabled by the combination of computing devices, application programming interfaces (APIs), and the proliferation of applications on user devices. 
     A social-networking system, which may include a social-networking website, may enable its users (such as persons or organizations) to interact with it and with each other through it. The social-networking system may, with input from a user, create and store in the social-networking system a user profile associated with the user. The user profile may include demographic information, communication-channel information, and information on personal interests of the user. The social-networking system may also, with input from a user, create and store a record of relationships of the user with other users of the social-networking system, as well as provide services (e.g., profile/news feed posts, photo-sharing, event organization, messaging, games, or advertisements) to facilitate social interaction between or among users. 
     The social-networking system may send over one or more networks content or messages related to its services to a mobile or other computing device of a user. A user may also install software applications on a mobile or other computing device of the user for accessing a user profile of the user and other data within the social-networking system. The social-networking system may generate a personalized set of content objects to display to a user, such as a newsfeed of aggregated stories of other users connected to the user. 
     SUMMARY OF PARTICULAR EMBODIMENTS 
     In particular embodiments, the assistant system may assist a user to obtain information or services. The assistant system may enable the user to interact with it with multi-modal user input (such as voice, text, image, video, motion) in stateful and multi-turn conversations to get assistance. As an example and not by way of limitation, the assistant system may support both audio (verbal) input and nonverbal input, such as vision, location, gesture, motion, or hybrid/multi-modal input. The assistant system may create and store a user profile comprising both personal and contextual information associated with the user. In particular embodiments, the assistant system may analyze the user input using natural-language understanding. The analysis may be based on the user profile of the user for more personalized and context-aware understanding. The assistant system may resolve entities associated with the user input based on the analysis. In particular embodiments, the assistant system may interact with different agents to obtain information or services that are associated with the resolved entities. The assistant system may generate a response for the user regarding the information or services by using natural-language generation. Through the interaction with the user, the assistant system may use dialog-management techniques to manage and advance the conversation flow with the user. In particular embodiments, the assistant system may further assist the user to effectively and efficiently digest the obtained information by summarizing the information. The assistant system may also assist the user to be more engaging with an online social network by providing tools that help the user interact with the online social network (e.g., creating posts, comments, messages). The assistant system may additionally assist the user to manage different tasks such as keeping track of events. In particular embodiments, the assistant system may proactively execute, without a user input, tasks that are relevant to user interests and preferences based on the user profile, at a time relevant for the user. In particular embodiments, the assistant system may check privacy settings to ensure that accessing a user&#39;s profile or other user information and executing different tasks are permitted subject to the user&#39;s privacy settings. 
     In particular embodiments, the assistant system may assist the user via a hybrid architecture built upon both client-side processes and server-side processes. The client-side processes and the server-side processes may be two parallel workflows for processing a user input and providing assistance to the user. In particular embodiments, the client-side processes may be performed locally on a client system associated with a user. By contrast, the server-side processes may be performed remotely on one or more computing systems. In particular embodiments, an arbitrator on the client system may coordinate receiving user input (e.g., an audio signal), determine whether to use a client-side process, a server-side process, or both, to respond to the user input, and analyze the processing results from each process. The arbitrator may instruct agents on the client-side or server-side to execute tasks associated with the user input based on the aforementioned analyses. The execution results may be further rendered as output to the client system. By leveraging both client-side and server-side processes, the assistant system can effectively assist a user with optimal usage of computing resources while at the same time protecting user privacy and enhancing security. 
     In particular embodiments, the assistant system may adaptively determine the most appropriate way to render content (e.g., notifications) to a user in real time on various client devices (e.g., smart glasses, AR glasses, VR headset, etc.) to prioritize relevant information for the user without distraction. As an example and not by way of limitation, for a client device that supports multimodal outputs, the content may be rendered visually, as sound, or as speech, and a variety of ways may exist within each of those modalities. To effectively determine how to render content, the assistant system may use various information including relevance of content, priority of content, user engagement, and user context from the user context engine. Among others, attention context and physio-social context may be two main types of user context that help with such determinization. Attention context may reveal how focused a user is on the assistant system or the client device with respect to the world. Physio-social context may reveal what the user is currently engaged with, e.g., alone, around other people but not interacting with them, and interacting with other people, etc. The user context engine may further map the relevance of content, priority of content, user engagement, and user context into different levels, with each of them corresponding to a different design of how the content should be rendered to the user. Although this disclosure describes rendering particular content by particular systems in a particular manner, this disclosure contemplates rending any suitable content by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system may receive a media content for delivery to a first user. The media content may be associated with a priority level. The assistant system may then access context information associated with the first user. In particular embodiments, the context information may be determined based on one or more multimodal signals from a client device associated with the first user. The assistant system may also determine a delivery level for the media content based on the priority level of the media content and the context information. In particular embodiments, the assistant system may further instruct the client device to present a notification associated with the media content to the first user. The notification may be rendered in one or more modalities determined based on the delivery level for the media content. 
     Certain technical challenges exist for generating context-aware notifications. One technical challenge may include determining what media contents and notifications to deliver to a user. The solutions presented by the embodiments disclosed herein to address this challenge may be applying different types of filters on media contents and notifications in combination with a user&#39;s distraction level and attitude as these filters reflect different levels of priorities and relevance of the media contents and notifications with respect to the user and the user&#39;s distraction level and attitude may help determine what types of filters to use to filter media contents and notifications. Another technical challenge may include determining when each of these modalities is appropriate to present to a user, particularly when deciding how much of each modality to make use of at a given time. The solution presented by the embodiments disclosed herein to address this challenge may be using context information to determine how a notification should be rendered as this way the assistant system may make sure such notification is contextually sensitive and not interrupting or distracting a user from real life or other high-priority activities. Another technical challenge may include determining a delivery level for the media content and notification. The solution presented by the embodiments disclosed herein to address this challenge may be determining the delivery level based on both physio-social context and focus level as they may capture the user&#39;s engagement with the surroundings and user activities. Another technical challenge may include determining the intensity for each of the modalities used to render the media content and notification. The solution presented by the embodiments disclosed herein to address this challenge may be determining the intensity based on a combination of different factors among user&#39;s engagement, degree of attention, user context, and relevance of content, as these factors may reflect the user&#39;s engagement with the surroundings and user activities and the importance of the media contents and notifications to the user. 
     Certain embodiments disclosed herein may provide one or more technical advantages. A technical advantage of the embodiments may include enabling the user to access the most suitable and relevant information without overwhelming the user by filtering out media contents and notifications based on their priority and relevance. Another technical advantage of the embodiments may include making a user feel connected to the assistant system but also engaged with the world as the assistant system may determine when each of the modalities for media contents and notifications is appropriate to present to the user. Certain embodiments disclosed herein may provide none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art in view of the figures, descriptions, and claims of the present disclosure. 
     The embodiments disclosed herein are only examples, and the scope of this disclosure is not limited to them. Particular embodiments may include all, some, or none of the components, elements, features, functions, operations, or steps of the embodiments disclosed herein. Embodiments according to the invention are in particular disclosed in the attached claims directed to a method, a storage medium, a system and a computer program product, wherein any feature mentioned in one claim category, e.g. method, can be claimed in another claim category, e.g. system, as well. The dependencies or references back in the attached claims are chosen for formal reasons only. However any subject matter resulting from a deliberate reference back to any previous claims (in particular multiple dependencies) can be claimed as well, so that any combination of claims and the features thereof are disclosed and can be claimed regardless of the dependencies chosen in the attached claims. The subject-matter which can be claimed comprises not only the combinations of features as set out in the attached claims but also any other combination of features in the claims, wherein each feature mentioned in the claims can be combined with any other feature or combination of other features in the claims. Furthermore, any of the embodiments and features described or depicted herein can be claimed in a separate claim and/or in any combination with any embodiment or feature described or depicted herein or with any of the features of the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example network environment associated with an assistant system. 
         FIG.  2    illustrates an example architecture of the assistant system. 
         FIG.  3    illustrates an example flow diagram of server-side processes of the assistant system. 
         FIG.  4    illustrates an example flow diagram of processing a user input by the assistant system. 
         FIG.  5    illustrates example correlations between relevance/priority and immediate attention requirement for different example notifications. 
         FIG.  6    illustrates an example notification matrix based on different combinations of filters and priorities. 
         FIG.  7    illustrates an example hierarchy of intensity of notification. 
         FIG.  8    illustrates example variance of intensity for notifications. 
         FIG.  9    illustrates an example visualization of how to deliver notifications based on a combination of factors. 
         FIG.  10    illustrates an example visualization of relevance, distraction level, and receptivity of different scenarios. 
         FIG.  11    illustrates an example notification of an incoming message while a user is running. 
         FIG.  12    illustrates an example notification of a reminder while a user is at a library. 
         FIG.  13    illustrates an example notification of a social-media post while a user is at a party. 
         FIG.  14    illustrates an example notification of new messages while a user is at a party. 
         FIG.  15    illustrates an example notification of an incoming message while a user is playing games. 
         FIG.  16    illustrates an example notification of traffic situation while a user is getting ready for work 
         FIG.  17    illustrates an example method for illustrates an example method for generating context-aware notifications. 
         FIG.  18    illustrates an example social graph. 
         FIG.  19    illustrates an example view of an embedding space. 
         FIG.  20    illustrates an example artificial neural network. 
         FIG.  21    illustrates an example computer system. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     System Overview 
       FIG.  1    illustrates an example network environment  100  associated with an assistant system. Network environment  100  includes a client system  130 , an assistant system  140 , a social-networking system  160 , and a third-party system  170  connected to each other by a network  110 . Although  FIG.  1    illustrates a particular arrangement of a client system  130 , an assistant system  140 , a social-networking system  160 , a third-party system  170 , and a network  110 , this disclosure contemplates any suitable arrangement of a client system  130 , an assistant system  140 , a social-networking system  160 , a third-party system  170 , and a network  110 . As an example and not by way of limitation, two or more of a client system  130 , a social-networking system  160 , an assistant system  140 , and a third-party system  170  may be connected to each other directly, bypassing a network  110 . As another example, two or more of a client system  130 , an assistant system  140 , a social-networking system  160 , and a third-party system  170  may be physically or logically co-located with each other in whole or in part. Moreover, although  FIG.  1    illustrates a particular number of client systems  130 , assistant systems  140 , social-networking systems  160 , third-party systems  170 , and networks  110 , this disclosure contemplates any suitable number of client systems  130 , assistant systems  140 , social-networking systems  160 , third-party systems  170 , and networks  110 . As an example and not by way of limitation, network environment  100  may include multiple client systems  130 , assistant systems  140 , social-networking systems  160 , third-party systems  170 , and networks  110 . 
     This disclosure contemplates any suitable network  110 . As an example and not by way of limitation, one or more portions of a network  110  may include an ad hoc network, an intranet, an extranet, a virtual private network (VPN), a local area network (LAN), a wireless LAN (WLAN), a wide area network (WAN), a wireless WAN (WWAN), a metropolitan area network (MAN), a portion of the Internet, a portion of the Public Switched Telephone Network (PSTN), a cellular telephone network, or a combination of two or more of these. A network  110  may include one or more networks  110 . 
     Links  150  may connect a client system  130 , an assistant system  140 , a social-networking system  160 , and a third-party system  170  to a communication network  110  or to each other. This disclosure contemplates any suitable links  150 . In particular embodiments, one or more links  150  include one or more wireline (such as for example Digital Subscriber Line (DSL) or Data Over Cable Service Interface Specification (DOCSIS)), wireless (such as for example Wi-Fi or Worldwide Interoperability for Microwave Access (WiMAX)), or optical (such as for example Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH)) links. In particular embodiments, one or more links  150  each include an ad hoc network, an intranet, an extranet, a VPN, a LAN, a WLAN, a WAN, a WWAN, a MAN, a portion of the Internet, a portion of the PSTN, a cellular technology-based network, a satellite communications technology-based network, another link  150 , or a combination of two or more such links  150 . Links  150  need not necessarily be the same throughout a network environment  100 . One or more first links  150  may differ in one or more respects from one or more second links  150 . 
     In particular embodiments, a client system  130  may be an electronic device including hardware, software, or embedded logic components or a combination of two or more such components and capable of carrying out the appropriate functionalities implemented or supported by a client system  130 . As an example and not by way of limitation, a client system  130  may include a computer system such as a desktop computer, notebook or laptop computer, netbook, a tablet computer, e-book reader, GPS device, camera, personal digital assistant (PDA), handheld electronic device, cellular telephone, smartphone, smart speaker, virtual reality (VR) headset, augment reality (AR) smart glasses, other suitable electronic device, or any suitable combination thereof. In particular embodiments, the client system  130  may be a smart assistant device. More information on smart assistant devices may be found in U.S. patent application Ser. No. 15/949011, filed 9 Apr. 2018, U.S. patent application Ser. No. 16/153574, filed 5 Oct. 2018, U.S. Design patent application Ser. No. 29/631910, filed 3 Jan. 2018, U.S. Design patent application Ser. No. 29/631747, filed 2 Jan. 2018, U.S. Design patent application Ser. No. 29/631913, filed 3 Jan. 2018, and U.S. Design patent application Ser. No. 29/631914, filed 3 Jan. 2018, each of which is incorporated by reference. This disclosure contemplates any suitable client systems  130 . A client system  130  may enable a network user at a client system  130  to access a network  110 . A client system  130  may enable its user to communicate with other users at other client systems  130 . 
     In particular embodiments, a client system  130  may include a web browser  132 , and may have one or more add-ons, plug-ins, or other extensions. A user at a client system  130  may enter a Uniform Resource Locator (URL) or other address directing a web browser  132  to a particular server (such as server  162 , or a server associated with a third-party system  170 ), and the web browser  132  may generate a Hyper Text Transfer Protocol (HTTP) request and communicate the HTTP request to server. The server may accept the HTTP request and communicate to a client system  130  one or more Hyper Text Markup Language (HTML) files responsive to the HTTP request. The client system  130  may render a web interface (e.g. a webpage) based on the HTML files from the server for presentation to the user. This disclosure contemplates any suitable source files. As an example and not by way of limitation, a web interface may be rendered from HTML files, Extensible Hyper Text Markup Language (XHTML) files, or Extensible Markup Language (XML) files, according to particular needs. Such interfaces may also execute scripts, combinations of markup language and scripts, and the like. Herein, reference to a web interface encompasses one or more corresponding source files (which a browser may use to render the web interface) and vice versa, where appropriate. 
     In particular embodiments, a client system  130  may include a social-networking application  134  installed on the client system  130 . A user at a client system  130  may use the social-networking application  134  to access on online social network. The user at the client system  130  may use the social-networking application  134  to communicate with the user&#39;s social connections (e.g., friends, followers, followed accounts, contacts, etc.). The user at the client system  130  may also use the social-networking application  134  to interact with a plurality of content objects (e.g., posts, news articles, ephemeral content, etc.) on the online social network. As an example and not by way of limitation, the user may browse trending topics and breaking news using the social-networking application  134 . 
     In particular embodiments, a client system  130  may include an assistant application  136 . A user at a client system  130  may use the assistant application  136  to interact with the assistant system  140 . In particular embodiments, the assistant application  136  may comprise a stand-alone application. In particular embodiments, the assistant application  136  may be integrated into the social-networking application  134  or another suitable application (e.g., a messaging application). In particular embodiments, the assistant application  136  may be also integrated into the client system  130 , an assistant hardware device, or any other suitable hardware devices. In particular embodiments, the assistant application  136  may be accessed via the web browser  132 . In particular embodiments, the user may provide input via different modalities. As an example and not by way of limitation, the modalities may include audio, text, image, video, motion, orientation, etc. The assistant application  136  may communicate the user input to the assistant system  140 . Based on the user input, the assistant system  140  may generate responses. The assistant system  140  may send the generated responses to the assistant application  136 . The assistant application  136  may then present the responses to the user at the client system  130 . The presented responses may be based on different modalities such as audio, text, image, and video. As an example and not by way of limitation, the user may verbally ask the assistant application  136  about the traffic information (i.e., via an audio modality) by speaking into a microphone of the client system  130 . The assistant application  136  may then communicate the request to the assistant system  140 . The assistant system  140  may accordingly generate a response and send it back to the assistant application  136 . The assistant application  136  may further present the response to the user in text and/or images on a display of the client system  130 . 
     In particular embodiments, an assistant system  140  may assist users to retrieve information from different sources. The assistant system  140  may also assist user to request services from different service providers. In particular embodiments, the assist system  140  may receive a user request for information or services via the assistant application  136  in the client system  130 . The assist system  140  may use natural-language understanding to analyze the user request based on user&#39;s profile and other relevant information. The result of the analysis may comprise different entities associated with an online social network. The assistant system  140  may then retrieve information or request services associated with these entities. In particular embodiments, the assistant system  140  may interact with the social-networking system  160  and/or third-party system  170  when retrieving information or requesting services for the user. In particular embodiments, the assistant system  140  may generate a personalized communication content for the user using natural-language generating techniques. The personalized communication content may comprise, for example, the retrieved information or the status of the requested services. In particular embodiments, the assistant system  140  may enable the user to interact with it regarding the information or services in a stateful and multi-turn conversation by using dialog-management techniques. The functionality of the assistant system  140  is described in more detail in the discussion of  FIG.  2    below. 
     In particular embodiments, the social-networking system  160  may be a network-addressable computing system that can host an online social network. The social-networking system  160  may generate, store, receive, and send social-networking data, such as, for example, user profile data, concept-profile data, social-graph information, or other suitable data related to the online social network. The social-networking system  160  may be accessed by the other components of network environment  100  either directly or via a network  110 . As an example and not by way of limitation, a client system  130  may access the social-networking system  160  using a web browser  132 , or a native application associated with the social-networking system  160  (e.g., a mobile social-networking application, a messaging application, another suitable application, or any combination thereof) either directly or via a network  110 . In particular embodiments, the social-networking system  160  may include one or more servers  162 . Each server  162  may be a unitary server or a distributed server spanning multiple computers or multiple datacenters. Servers  162  may be of various types, such as, for example and without limitation, web server, news server, mail server, message server, advertising server, file server, application server, exchange server, database server, proxy server, another server suitable for performing functions or processes described herein, or any combination thereof. In particular embodiments, each server  162  may include hardware, software, or embedded logic components or a combination of two or more such components for carrying out the appropriate functionalities implemented or supported by server  162 . In particular embodiments, the social-networking system  160  may include one or more data stores  164 . Data stores  164  may be used to store various types of information. In particular embodiments, the information stored in data stores  164  may be organized according to specific data structures. In particular embodiments, each data store  164  may be a relational, columnar, correlation, or other suitable database. Although this disclosure describes or illustrates particular types of databases, this disclosure contemplates any suitable types of databases. Particular embodiments may provide interfaces that enable a client system  130 , a social-networking system  160 , an assistant system  140 , or a third-party system  170  to manage, retrieve, modify, add, or delete, the information stored in data store  164 . 
     In particular embodiments, the social-networking system  160  may store one or more social graphs in one or more data stores  164 . In particular embodiments, a social graph may include multiple nodes—which may include multiple user nodes (each corresponding to a particular user) or multiple concept nodes (each corresponding to a particular concept)—and multiple edges connecting the nodes. The social-networking system  160  may provide users of the online social network the ability to communicate and interact with other users. In particular embodiments, users may join the online social network via the social-networking system  160  and then add connections (e.g., relationships) to a number of other users of the social-networking system  160  whom they want to be connected to. Herein, the term “friend” may refer to any other user of the social-networking system  160  with whom a user has formed a connection, association, or relationship via the social-networking system  160 . 
     In particular embodiments, the social-networking system  160  may provide users with the ability to take actions on various types of items or objects, supported by the social-networking system  160 . As an example and not by way of limitation, the items and objects may include groups or social networks to which users of the social-networking system  160  may belong, events or calendar entries in which a user might be interested, computer-based applications that a user may use, transactions that allow users to buy or sell items via the service, interactions with advertisements that a user may perform, or other suitable items or objects. A user may interact with anything that is capable of being represented in the social-networking system  160  or by an external system of a third-party system  170 , which is separate from the social-networking system  160  and coupled to the social-networking system  160  via a network  110 . 
     In particular embodiments, the social-networking system  160  may be capable of linking a variety of entities. As an example and not by way of limitation, the social-networking system  160  may enable users to interact with each other as well as receive content from third-party systems  170  or other entities, or to allow users to interact with these entities through an application programming interfaces (API) or other communication channels. 
     In particular embodiments, a third-party system  170  may include one or more types of servers, one or more data stores, one or more interfaces, including but not limited to APIs, one or more web services, one or more content sources, one or more networks, or any other suitable components, e.g., that servers may communicate with. A third-party system  170  may be operated by a different entity from an entity operating the social-networking system  160 . In particular embodiments, however, the social-networking system  160  and third-party systems  170  may operate in conjunction with each other to provide social-networking services to users of the social-networking system  160  or third-party systems  170 . In this sense, the social-networking system  160  may provide a platform, or backbone, which other systems, such as third-party systems  170 , may use to provide social-networking services and functionality to users across the Internet. 
     In particular embodiments, a third-party system  170  may include a third-party content object provider. A third-party content object provider may include one or more sources of content objects, which may be communicated to a client system  130 . As an example and not by way of limitation, content objects may include information regarding things or activities of interest to the user, such as, for example, movie show times, movie reviews, restaurant reviews, restaurant menus, product information and reviews, or other suitable information. As another example and not by way of limitation, content objects may include incentive content objects, such as coupons, discount tickets, gift certificates, or other suitable incentive objects. In particular embodiments, a third-party content provider may use one or more third-party agents to provide content objects and/or services. A third-party agent may be an implementation that is hosted and executing on the third-party system  170 . 
     In particular embodiments, the social-networking system  160  also includes user-generated content objects, which may enhance a user&#39;s interactions with the social-networking system  160 . User-generated content may include anything a user can add, upload, send, or “post” to the social-networking system  160 . As an example and not by way of limitation, a user communicates posts to the social-networking system  160  from a client system  130 . Posts may include data such as status updates or other textual data, location information, photos, videos, links, music or other similar data or media. Content may also be added to the social-networking system  160  by a third-party through a “communication channel,” such as a newsfeed or stream. 
     In particular embodiments, the social-networking system  160  may include a variety of servers, sub-systems, programs, modules, logs, and data stores. In particular embodiments, the social-networking system  160  may include one or more of the following: a web server, action logger, API-request server, relevance-and-ranking engine, content-object classifier, notification controller, action log, third-party-content-object-exposure log, inference module, authorization/privacy server, search module, advertisement-targeting module, user-interface module, user-profile store, connection store, third-party content store, or location store. The social-networking system  160  may also include suitable components such as network interfaces, security mechanisms, load balancers, failover servers, management-and-network-operations consoles, other suitable components, or any suitable combination thereof. In particular embodiments, the social-networking system  160  may include one or more user-profile stores for storing user profiles. A user profile may include, for example, biographic information, demographic information, behavioral information, social information, or other types of descriptive information, such as work experience, educational history, hobbies or preferences, interests, affinities, or location. Interest information may include interests related to one or more categories. Categories may be general or specific. As an example and not by way of limitation, if a user “likes” an article about a brand of shoes the category may be the brand, or the general category of “shoes” or “clothing.” A connection store may be used for storing connection information about users. The connection information may indicate users who have similar or common work experience, group memberships, hobbies, educational history, or are in any way related or share common attributes. The connection information may also include user-defined connections between different users and content (both internal and external). A web server may be used for linking the social-networking system  160  to one or more client systems  130  or one or more third-party systems  170  via a network  110 . The web server may include a mail server or other messaging functionality for receiving and routing messages between the social-networking system  160  and one or more client systems  130 . An API-request server may allow, for example, an assistant system  140  or a third-party system  170  to access information from the social-networking system  160  by calling one or more APIs. An action logger may be used to receive communications from a web server about a user&#39;s actions on or off the social-networking system  160 . In conjunction with the action log, a third-party-content-object log may be maintained of user exposures to third-party-content objects. A notification controller may provide information regarding content objects to a client system  130 . Information may be pushed to a client system  130  as notifications, or information may be pulled from a client system  130  responsive to a request received from a client system  130 . Authorization servers may be used to enforce one or more privacy settings of the users of the social-networking system  160 . A privacy setting of a user determines how particular information associated with a user can be shared. The authorization server may allow users to opt in to or opt out of having their actions logged by the social-networking system  160  or shared with other systems (e.g., a third-party system  170 ), such as, for example, by setting appropriate privacy settings. Third-party-content-object stores may be used to store content objects received from third parties, such as a third-party system  170 . Location stores may be used for storing location information received from client systems  130  associated with users. Advertisement-pricing modules may combine social information, the current time, location information, or other suitable information to provide relevant advertisements, in the form of notifications, to a user. 
     Assistant Systems 
       FIG.  2    illustrates an example architecture of an assistant system  140 . In particular embodiments, the assistant system  140  may assist a user to obtain information or services. The assistant system  140  may enable the user to interact with it with multi-modal user input (such as voice, text, image, video, motion) in stateful and multi-turn conversations to get assistance. As an example and not by way of limitation, the assistant system  140  may support both audio input (verbal) and nonverbal input, such as vision, location, gesture, motion, or hybrid/multi-modal input. The assistant system  140  may create and store a user profile comprising both personal and contextual information associated with the user. In particular embodiments, the assistant system  140  may analyze the user input using natural-language understanding. The analysis may be based on the user profile of the user for more personalized and context-aware understanding. The assistant system  140  may resolve entities associated with the user input based on the analysis. In particular embodiments, the assistant system  140  may interact with different agents to obtain information or services that are associated with the resolved entities. The assistant system  140  may generate a response for the user regarding the information or services by using natural-language generation. Through the interaction with the user, the assistant system  140  may use dialog management techniques to manage and forward the conversation flow with the user. In particular embodiments, the assistant system  140  may further assist the user to effectively and efficiently digest the obtained information by summarizing the information. The assistant system  140  may also assist the user to be more engaging with an online social network by providing tools that help the user interact with the online social network (e.g., creating posts, comments, messages). The assistant system  140  may additionally assist the user to manage different tasks such as keeping track of events. In particular embodiments, the assistant system  140  may proactively execute, without a user input, pre-authorized tasks that are relevant to user interests and preferences based on the user profile, at a time relevant for the user. In particular embodiments, the assistant system  140  may check privacy settings to ensure that accessing a user&#39;s profile or other user information and executing different tasks are permitted subject to the user&#39;s privacy settings. More information on assisting users subject to privacy settings may be found in U.S. patent application Ser. No. 16/182542, filed 6 Nov. 2018, which is incorporated by reference. 
     In particular embodiments, the assistant system  140  may assist the user via a hybrid architecture built upon both client-side processes and server-side processes. The client-side processes and the server-side processes may be two parallel workflows for processing a user input and providing assistances to the user. In particular embodiments, the client-side processes may be performed locally on a client system  130  associated with a user. By contrast, the server-side processes may be performed remotely on one or more computing systems. In particular embodiments, an assistant orchestrator on the client system  130  may coordinate receiving user input (e.g., audio signal) and determine whether to use client-side processes, server-side processes, or both, to respond to the user input. A dialog arbitrator may analyze the processing results from each process. The dialog arbitrator may instruct agents on the client-side or server-side to execute tasks associated with the user input based on the aforementioned analyses. The execution results may be further rendered as output to the client system  130 . By leveraging both client-side and server-side processes, the assistant system  140  can effectively assist a user with optimal usage of computing resources while at the same time protecting user privacy and enhancing security. 
     In particular embodiments, the assistant system  140  may receive a user input from a client system  130  associated with the user. In particular embodiments, the user input may be a user-generated input that is sent to the assistant system  140  in a single turn. The user input may be verbal, nonverbal, or a combination thereof. As an example and not by way of limitation, the nonverbal user input may be based on the user&#39;s voice, vision, location, activity, gesture, motion, or a combination thereof. If the user input is based on the user&#39;s voice (e.g., the user may speak to the client system  130 ), such user input may be first processed by a system audio API  202  (application programming interface). The system audio API  202  may conduct echo cancellation, noise removal, beam forming, and self-user voice activation, speaker identification, voice activity detection (VAD), and any other acoustic techniques to generate audio data that is readily processable by the assistant system  140 . In particular embodiments, the system audio API  202  may perform wake-word detection  204  from the user input. As an example and not by way of limitation, a wake-word may be “hey assistant”. If such wake-word is detected, the assistant system  140  may be activated accordingly. In alternative embodiments, the user may activate the assistant system  140  via a visual signal without a wake-word. The visual signal may be received at a low-power sensor (e.g., a camera) that can detect various visual signals. As an example and not by way of limitation, the visual signal may be a barcode, a QR code or a universal product code (UPC) detected by the client system  130 . As another example and not by way of limitation, the visual signal may be the user&#39;s gaze at an object. As yet another example and not by way of limitation, the visual signal may be a user gesture, e.g., the user pointing at an object. 
     In particular embodiments, the audio data from the system audio API  202  may be sent to an assistant orchestrator  206 . The assistant orchestrator  206  may be executing on the client system  130 . In particular embodiments, the assistant orchestrator  206  may determine whether to respond to the user input by using client-side processes, server-side processes, or both. As indicated in  FIG.  2   , the client-side processes are illustrated below the dashed line  207  whereas the server-side processes are illustrated above the dashed line  207 . The assistant orchestrator  206  may also determine to respond to the user input by using both the client-side processes and the server-side processes simultaneously. Although  FIG.  2    illustrates the assistant orchestrator  206  as being a client-side process, the assistant orchestrator  206  may be a server-side process or may be a hybrid process split between client- and server-side processes. 
     In particular embodiments, the server-side processes may be as follows after audio data is generated from the system audio API  202 . The assistant orchestrator  206  may send the audio data to a remote computing system that hosts different modules of the assistant system  140  to respond to the user input. In particular embodiments, the audio data may be received at a remote automatic speech recognition (ASR) module  208 . The ASR module  208  may allow a user to dictate and have speech transcribed as written text, have a document synthesized as an audio stream, or issue commands that are recognized as such by the system. The ASR module  208  may use statistical models to determine the most likely sequences of words that correspond to a given portion of speech received by the assistant system  140  as audio input. The models may include one or more of hidden Markov models, neural networks, deep learning models, or any combination thereof. The received audio input may be encoded into digital data at a particular sampling rate (e.g., 16, 44.1, or 96 kHz) and with a particular number of bits representing each sample (e.g., 8, 16, of 24 bits). 
     In particular embodiments, the ASR module  208  may comprise different components. The ASR module  208  may comprise one or more of a grapheme-to-phoneme (G2P) model, a pronunciation learning model, a personalized acoustic model, a personalized language model (PLM), or an end-pointing model. In particular embodiments, the G2P model may be used to determine a user&#39;s grapheme-to-phoneme style, e.g., what it may sound like when a particular user speaks a particular word. The personalized acoustic model may be a model of the relationship between audio signals and the sounds of phonetic units in the language. Therefore, such personalized acoustic model may identify how a user&#39;s voice sounds. The personalized acoustical model may be generated using training data such as training speech received as audio input and the corresponding phonetic units that correspond to the speech. The personalized acoustical model may be trained or refined using the voice of a particular user to recognize that user&#39;s speech. In particular embodiments, the personalized language model may then determine the most likely phrase that corresponds to the identified phonetic units for a particular audio input. The personalized language model may be a model of the probabilities that various word sequences may occur in the language. The sounds of the phonetic units in the audio input may be matched with word sequences using the personalized language model, and greater weights may be assigned to the word sequences that are more likely to be phrases in the language. The word sequence having the highest weight may be then selected as the text that corresponds to the audio input. In particular embodiments, the personalized language model may be also used to predict what words a user is most likely to say given a context. In particular embodiments, the end-pointing model may detect when the end of an utterance is reached. 
     In particular embodiments, the output of the ASR module  208  may be sent to a remote natural-language understanding (NLU) module  210 . The NLU module  210  may perform named entity resolution (NER). The NLU module  210  may additionally consider contextual information when analyzing the user input. In particular embodiments, an intent and/or a slot may be an output of the NLU module  210 . An intent may be an element in a pre-defined taxonomy of semantic intentions, which may indicate a purpose of a user interacting with the assistant system  140 . The NLU module  210  may classify a user input into a member of the pre-defined taxonomy, e.g., for the input “Play Beethoven&#39;s 5th,” the NLU module  210  may classify the input as having the intent [IN:play_music]. In particular embodiments, a domain may denote a social context of interaction, e.g., education, or a namespace for a set of intents, e.g., music. A slot may be a named sub-string corresponding to a character string within the user input, representing a basic semantic entity. For example, a slot for “pizza” may be [SL:dish]. In particular embodiments, a set of valid or expected named slots may be conditioned on the classified intent. As an example and not by way of limitation, for the intent [IN:play_music], a valid slot may be [SL:song_name]. In particular embodiments, the NLU module  210  may additionally extract information from one or more of a social graph, a knowledge graph, or a concept graph, and retrieve a user&#39;s profile from one or more remote data stores  212 . The NLU module  210  may further process information from these different sources by determining what information to aggregate, annotating n-grams of the user input, ranking the n-grams with confidence scores based on the aggregated information, and formulating the ranked n-grams into features that can be used by the NLU module  210  for understanding the user input. 
     In particular embodiments, the NLU module  210  may identify one or more of a domain, an intent, or a slot from the user input in a personalized and context-aware manner. As an example and not by way of limitation, a user input may comprise “show me how to get to the coffee shop”. The NLU module  210  may identify the particular coffee shop that the user wants to go based on the user&#39;s personal information and the associated contextual information. In particular embodiments, the NLU module  210  may comprise a lexicon of a particular language and a parser and grammar rules to partition sentences into an internal representation. The NLU module  210  may also comprise one or more programs that perform naive semantics or stochastic semantic analysis to the use of pragmatics to understand a user input. In particular embodiments, the parser may be based on a deep learning architecture comprising multiple long-short term memory (LSTM) networks. As an example and not by way of limitation, the parser may be based on a recurrent neural network grammar (RNNG) model, which is a type of recurrent and recursive LSTM algorithm. More information on natural-language understanding may be found in U.S. patent application Ser. No. 16/011062, filed 18 Jun. 2018, U.S. patent application Ser. No. 16/025317, filed 2 Jul. 2018, and U.S. patent application Ser. No. 16/038120, filed 17 Jul. 2018, each of which is incorporated by reference. 
     In particular embodiments, the output of the NLU module  210  may be sent to a remote reasoning module  214 . The reasoning module  214  may comprise a dialog manager and an entity resolution component. In particular embodiments, the dialog manager may have complex dialog logic and product-related business logic. The dialog manager may manage the dialog state and flow of the conversation between the user and the assistant system  140 . The dialog manager may additionally store previous conversations between the user and the assistant system  140 . In particular embodiments, the dialog manager may communicate with the entity resolution component to resolve entities associated with the one or more slots, which supports the dialog manager to advance the flow of the conversation between the user and the assistant system  140 . In particular embodiments, the entity resolution component may access one or more of the social graph, the knowledge graph, or the concept graph when resolving the entities. Entities may include, for example, unique users or concepts, each of which may have a unique identifier (ID). As an example and not by way of limitation, the knowledge graph may comprise a plurality of entities. Each entity may comprise a single record associated with one or more attribute values. The particular record may be associated with a unique entity identifier. Each record may have diverse values for an attribute of the entity. Each attribute value may be associated with a confidence probability. A confidence probability for an attribute value represents a probability that the value is accurate for the given attribute. Each attribute value may be also associated with a semantic weight. A semantic weight for an attribute value may represent how the value semantically appropriate for the given attribute considering all the available information. For example, the knowledge graph may comprise an entity of a book “Alice&#39;s Adventures”, which includes information that has been extracted from multiple content sources (e.g., an online social network, online encyclopedias, book review sources, media databases, and entertainment content sources), and then deduped, resolved, and fused to generate the single unique record for the knowledge graph. The entity may be associated with a “fantasy” attribute value which indicates the genre of the book “Alice&#39;s Adventures”. More information on the knowledge graph may be found in U.S. patent application Ser. No. 16/048049, filed 27 Jul. 2018, and U.S. patent application Ser. No. 16/048101, filed 27 Jul. 2018, each of which is incorporated by reference. 
     In particular embodiments, the entity resolution component may check the privacy constraints to guarantee that the resolving of the entities does not violate privacy policies. As an example and not by way of limitation, an entity to be resolved may be another user who specifies in his/her privacy settings that his/her identity should not be searchable on the online social network, and thus the entity resolution component may not return that user&#39;s identifier in response to a request. Based on the information obtained from the social graph, the knowledge graph, the concept graph, and the user profile, and subject to applicable privacy policies, the entity resolution component may therefore resolve the entities associated with the user input in a personalized, context-aware, and privacy-aware manner. In particular embodiments, each of the resolved entities may be associated with one or more identifiers hosted by the social-networking system  160 . As an example and not by way of limitation, an identifier may comprise a unique user identifier (ID) corresponding to a particular user (e.g., a unique username or user ID number). In particular embodiments, each of the resolved entities may be also associated with a confidence score. More information on resolving entities may be found in U.S. patent application Ser. No. 16/048049, filed 27 Jul. 2018, and U.S. patent application Ser. No. 16/048072, filed 27 Jul. 2018, each of which is incorporated by reference. 
     In particular embodiments, the dialog manager may conduct dialog optimization and assistant state tracking. Dialog optimization is the problem of using data to understand what the most likely branching in a dialog should be. As an example and not by way of limitation, with dialog optimization the assistant system  140  may not need to confirm who a user wants to call because the assistant system  140  has high confidence that a person inferred based on dialog optimization would be very likely whom the user wants to call. In particular embodiments, the dialog manager may use reinforcement learning for dialog optimization. Assistant state tracking aims to keep track of a state that changes over time as a user interacts with the world and the assistant system  140  interacts with the user. As an example and not by way of limitation, assistant state tracking may track what a user is talking about, whom the user is with, where the user is, what tasks are currently in progress, and where the user&#39;s gaze is at, etc., subject to applicable privacy policies. In particular embodiments, the dialog manager may use a set of operators to track the dialog state. The operators may comprise the necessary data and logic to update the dialog state. Each operator may act as delta of the dialog state after processing an incoming request. In particular embodiments, the dialog manager may further comprise a dialog state tracker and an action selector. In alternative embodiments, the dialog state tracker may replace the entity resolution component and resolve the references/mentions and keep track of the state. 
     In particular embodiments, the reasoning module  214  may further conduct false trigger mitigation. The goal of false trigger mitigation is to detect false triggers (e.g., wake-word) of assistance requests and to avoid generating false records when a user actually does not intend to invoke the assistant system  140 . As an example and not by way of limitation, the reasoning module  214  may achieve false trigger mitigation based on a nonsense detector. If the nonsense detector determines that a wake-word makes no sense at this point in the interaction with the user, the reasoning module  214  may determine that inferring the user intended to invoke the assistant system  140  may be incorrect. In particular embodiments, the output of the reasoning module  214  may be sent a remote dialog arbitrator  216 . 
     In particular embodiments, each of the ASR module  208 , NLU module  210 , and reasoning module  214  may access the remote data store  212 , which comprises user episodic memories to determine how to assist a user more effectively. More information on episodic memories may be found in U.S. patent application Ser. No. 16/552559, filed 27 Aug. 2019, which is incorporated by reference. The data store  212  may additionally store the user profile of the user. The user profile of the user may comprise user profile data including demographic information, social information, and contextual information associated with the user. The user profile data may also include user interests and preferences on a plurality of topics, aggregated through conversations on news feed, search logs, messaging platforms, etc. The usage of a user profile may be subject to privacy constraints to ensure that a user&#39;s information can be used only for his/her benefit, and not shared with anyone else. More information on user profiles may be found in U.S. patent application Ser. No. 15/967239, filed 30 Apr. 2018, which is incorporated by reference. 
     In particular embodiments, parallel to the aforementioned server-side process involving the ASR module  208 , NLU module  210 , and reasoning module  214 , the client-side process may be as follows. In particular embodiments, the output of the assistant orchestrator  206  may be sent to a local ASR module  216  on the client system  130 . The ASR module  216  may comprise a personalized language model (PLM), a G2P model, and an end-pointing model. Because of the limited computing power of the client system  130 , the assistant system  140  may optimize the personalized language model at run time during the client-side process. As an example and not by way of limitation, the assistant system  140  may pre-compute a plurality of personalized language models for a plurality of possible subjects a user may talk about. When a user requests assistance, the assistant system  140  may then swap these pre-computed language models quickly so that the personalized language model may be optimized locally by the assistant system  140  at run time based on user activities. As a result, the assistant system  140  may have a technical advantage of saving computational resources while efficiently determining what the user may be talking about. In particular embodiments, the assistant system  140  may also re-learn user pronunciations quickly at run time. 
     In particular embodiments, the output of the ASR module  216  may be sent to a local NLU module  218 . In particular embodiments, the NLU module  218  herein may be more compact compared to the remote NLU module  210  supported on the server-side. When the ASR module  216  and NLU module  218  process the user input, they may access a local assistant memory  220 . The local assistant memory  220  may be different from the user memories stored on the data store  212  for the purpose of protecting user privacy. In particular embodiments, the local assistant memory  220  may be syncing with the user memories stored on the data store  212  via the network  110 . As an example and not by way of limitation, the local assistant memory  220  may sync a calendar on a user&#39;s client system  130  with a server-side calendar associate with the user. In particular embodiments, any secured data in the local assistant memory  220  may be only accessible to the modules of the assistant system  140  that are locally executing on the client system  130 . 
     In particular embodiments, the output of the NLU module  218  may be sent to a local reasoning module  222 . The reasoning module  222  may comprise a dialog manager and an entity resolution component. Due to the limited computing power, the reasoning module  222  may conduct on-device learning that is based on learning algorithms particularly tailored for client systems  130 . As an example and not by way of limitation, federated learning may be used by the reasoning module  222 . Federated learning is a specific category of distributed machine learning approaches which trains machine learning models using decentralized data residing on end devices such as mobile phones. In particular embodiments, the reasoning module  222  may use a particular federated learning model, namely federated user representation learning, to extend existing neural-network personalization techniques to federated learning. Federated user representation learning can personalize models in federated learning by learning task-specific user representations (i.e., embeddings) or by personalizing model weights. Federated user representation learning is a simple, scalable, privacy-preserving, and resource-efficient. Federated user representation learning may divide model parameters into federated and private parameters. Private parameters, such as private user embeddings, may be trained locally on a client system  130  instead of being transferred to or averaged on a remote server. Federated parameters, by contrast, may be trained remotely on the server. In particular embodiments, the reasoning module  222  may use another particular federated learning model, namely active federated learning to transmit a global model trained on the remote server to client systems  130  and calculate gradients locally on these client systems  130 . Active federated learning may enable the reasoning module to minimize the transmission costs associated with downloading models and uploading gradients. For active federated learning, in each round client systems are selected not uniformly at random, but with a probability conditioned on the current model and the data on the client systems to maximize efficiency. In particular embodiments, the reasoning module  222  may use another particular federated learning model, namely federated Adam. Conventional federated learning model may use stochastic gradient descent (SGD) optimizers. By contrast, the federated Adam model may use moment-based optimizers. Instead of using the averaged model directly as what conventional work does, federated Adam model may use the averaged model to compute approximate gradients. These gradients may be then fed into the federated Adam model, which may de-noise stochastic gradients and use a per-parameter adaptive learning rate. Gradients produced by federated learning may be even noisier than stochastic gradient descent (because data may be not independent and identically distributed), so federated Adam model may help even more deal with the noise. The federated Adam model may use the gradients to take smarter steps towards minimizing the objective function. The experiments show that conventional federated learning on a benchmark has 1.6% drop in ROC (Receiver Operating Characteristics) curve whereas federated Adam model has only 0.4% drop. In addition, federated Adam model has no increase in communication or on-device computation. In particular embodiments, the reasoning module  222  may also perform false trigger mitigation. This false trigger mitigation may help detect false activation requests, e.g., wake-word, on the client system  130  when the user&#39;s speech input comprises data that is subject to privacy constraints. As an example and not by way of limitation, when a user is in a voice call, the user&#39;s conversation is private and the false trigger detection based on such conversation can only occur locally on the user&#39;s client system  130 . 
     In particular embodiments, the assistant system  140  may comprise a local context engine  224 . The context engine  224  may process all the other available signals to provide more informative cues to the reasoning module  222 . As an example and not by way of limitation, the context engine  224  may have information related to people, sensory data from client system  130  sensors (e.g., microphone, camera) that are further analyzed by computer vision technologies, geometry constructions, activity data, inertial data (e.g., collected by a VR headset), location, etc. In particular embodiments, the computer vision technologies may comprise human skeleton reconstruction, face detection, facial recognition, hand tracking, eye tracking, etc. In particular embodiments, geometry constructions may comprise constructing objects surrounding a user using data collected by a client system  130 . As an example and not by way of limitation, the user may be wearing AR glasses and geometry construction may aim to determine where the floor is, where the wall is, where the user&#39;s hands are, etc. In particular embodiments, inertial data may be data associated with linear and angular motions. As an example and not by way of limitation, inertial data may be captured by AR glasses which measures how a user&#39;s body parts move. 
     In particular embodiments, the output of the local reasoning module  222  may be sent to the dialog arbitrator  216 . The dialog arbitrator  216  may function differently in three scenarios. In the first scenario, the assistant orchestrator  206  determines to use server-side process, for which the dialog arbitrator  216  may transmit the output of the reasoning module  214  to a remote action execution module  226 . In the second scenario, the assistant orchestrator  206  determines to use both server-side processes and client-side processes, for which the dialog arbitrator  216  may aggregate output from both reasoning modules (i.e., remote reasoning module  214  and local reasoning module  222 ) of both processes and analyze them. As an example and not by way of limitation, the dialog arbitrator  216  may perform ranking and select the best reasoning result for responding to the user input. In particular embodiments, the dialog arbitrator  216  may further determine whether to use agents on the server-side or on the client-side to execute relevant tasks based on the analysis. In the third scenario, the assistant orchestrator  206  determines to use client-side processes and the dialog arbitrator  216  needs to evaluate the output of the local reasoning module  222  to determine if the client-side processes can complete the task of handling the user input. In alternative embodiments, the output of the reasoning module  222  may be not sent to the dialog arbitrator  216  if the assistant orchestrator  206  determines to use client-side processes and that client-side processes are fully capable of processing the user input. 
     In particular embodiments, for the first and second scenarios mentioned above, the dialog arbitrator  216  may determine that the agents on the server-side are necessary to execute tasks responsive to the user input. Accordingly, the dialog arbitrator  216  may send necessary information regarding the user input to the action execution module  226 . The action execution module  226  may call one or more agents to execute the tasks. In alternative embodiments, the action selector of the dialog manager may determine actions to execute and instruct the action execution module  226  accordingly. In particular embodiments, an agent may be an implementation that serves as a broker across a plurality of content providers for one domain. A content provider may be an entity responsible for carrying out an action associated with an intent or completing a task associated with the intent. In particular embodiments, the agents may comprise first-party agents and third-party agents. In particular embodiments, first-party agents may comprise internal agents that are accessible and controllable by the assistant system  140  (e.g. agents associated with services provided by the online social network, such as messaging services or photo-share services). In particular embodiments, third-party agents may comprise external agents that the assistant system  140  has no control over (e.g., third-party online music application agents, ticket sales agents). The first-party agents may be associated with first-party providers that provide content objects and/or services hosted by the social-networking system  160 . The third-party agents may be associated with third-party providers that provide content objects and/or services hosted by the third-party system  170 . In particular embodiments, each of the first-party agents or third-party agents may be designated for a particular domain. As an example and not by way of limitation, the domain may comprise weather, transportation, music, shopping, social, videos, photos, events, locations, work, etc. In particular embodiments, the assistant system  140  may use a plurality of agents collaboratively to respond to a user input. As an example and not by way of limitation, the user input may comprise “direct me to my next meeting.” The assistant system  140  may use a calendar agent to retrieve the location of the next meeting. The assistant system  140  may then use a navigation agent to direct the user to the next meeting. 
     In particular embodiments, for the second and third scenarios mentioned above, the dialog arbitrator  216  may determine that the agents on the client-side are capable of executing tasks responsive to the user input but additional information is needed (e.g., response templates) or that the tasks can be only handled by the agents on the server-side. If the dialog arbitrator  216  determines that the tasks can be only handled by the agents on the server-side, the dialog arbitrator  216  may send necessary information regarding the user input to the action execution module  226 . If the dialog arbitrator  216  determines that the agents on the client-side are capable of executing tasks but response templates are needed, the dialog arbitrator  216  may send necessary information regarding the user input to a remote response template generation module  228 . The output of the response template generation module  228  may be further sent to a local action execution module  230  executing on the client system  130 . In particular embodiments, if the assistant orchestrator  206  determines to use client-side processes and that client-side processes are fully capable of processing the user input, the output of the reasoning module  222  may be directly sent to the action execution module  230 . 
     In particular embodiments, the action execution module  230  may call local agents to execute tasks. A local agent on the client system  130  may be able to execute simpler tasks compared to an agent on the server-side. As an example and not by way of limitation, multiple device-specific implementations (e.g., real-time calls for a client system  130  or a messaging application on the client system  130 ) may be handled internally by a single agent. Alternatively, these device-specific implementations may be handled by multiple agents associated with multiple domains. In particular embodiments, the action execution module  230  may additionally perform a set of general executable dialog actions. The set of executable dialog actions may interact with agents, users and the assistant system  140  itself. These dialog actions may comprise dialog actions for slot request, confirmation, disambiguation, agent execution, etc. The dialog actions may be independent of the underlying implementation of the action selector or dialog policy. Both tree-based policy and model-based policy may generate the same basic dialog actions, with a callback function hiding any action selector specific implementation details. 
     In particular embodiments, the output from the remote action execution module  226  on the server-side may be sent to a remote response execution module  232 . In particular embodiments, the action execution module  226  may communicate back to the dialog arbitrator  216  for more information. The response execution module  232  may be based on a remote conversational understanding (CU) composer. In particular embodiments, the output from the action execution module  226  may be formulated as a &lt;k, c, u, d &gt; tuple, in which k indicates a knowledge source, c indicates a communicative goal, u indicates a user model, and d indicates a discourse model. In particular embodiments, the CU composer may comprise a natural-language generation (NLG) module and a user interface (UI) payload generator. The natural-language generator may generate a communication content based on the output of the action execution module  226  using different language models and/or language templates. In particular embodiments, the generation of the communication content may be application specific and also personalized for each user. The CU composer may also determine a modality of the generated communication content using the UI payload generator. In particular embodiments, the NLG module may comprise a content determination component, a sentence planner, and a surface realization component. The content determination component may determine the communication content based on the knowledge source, communicative goal, and the user&#39;s expectations. As an example and not by way of limitation, the determining may be based on a description logic. The description logic may comprise, for example, three fundamental notions which are individuals (representing objects in the domain), concepts (describing sets of individuals), and roles (representing binary relations between individuals or concepts). The description logic may be characterized by a set of constructors that allow the natural-language generator to build complex concepts/roles from atomic ones. In particular embodiments, the content determination component may perform the following tasks to determine the communication content. The first task may comprise a translation task, in which the input to the natural-language generator may be translated to concepts. The second task may comprise a selection task, in which relevant concepts may be selected among those resulted from the translation task based on the user model. The third task may comprise a verification task, in which the coherence of the selected concepts may be verified. The fourth task may comprise an instantiation task, in which the verified concepts may be instantiated as an executable file that can be processed by the natural-language generator. The sentence planner may determine the organization of the communication content to make it human understandable. The surface realization component may determine specific words to use, the sequence of the sentences, and the style of the communication content. The UI payload generator may determine a preferred modality of the communication content to be presented to the user. In particular embodiments, the CU composer may check privacy constraints associated with the user to make sure the generation of the communication content follows the privacy policies. More information on natural-language generation may be found in U.S. patent application Ser. No. 15/967279, filed 30 Apr. 2018, and U.S. patent application Ser. No. 15/966455, filed 30 Apr. 2018, each of which is incorporated by reference. 
     In particular embodiments, the output from the local action execution module  230  on the client system  130  may be sent to a local response execution module  234 . The response execution module  234  may be based on a local conversational understanding (CU) composer. The CU composer may comprise a natural-language generation (NLG) module. As the computing power of a client system  130  may be limited, the NLG module may be simple for the consideration of computational efficiency. Because the NLG module may be simple, the output of the response execution module  234  may be sent to a local response expansion module  236 . The response expansion module  236  may further expand the result of the response execution module  234  to make a response more natural and contain richer semantic information. 
     In particular embodiments, if the user input is based on audio signals, the output of the response execution module  232  on the server-side may be sent to a remote text-to-speech (TTS) module  238 . Similarly, the output of the response expansion module  236  on the client-side may be sent to a local TTS module  240 . Both TTS modules may convert a response to audio signals. In particular embodiments, the output from the response execution module  232 , the response expansion module  236 , or the TTS modules on both sides, may be finally sent to a local render output module  242 . The render output module  242  may generate a response that is suitable for the client system  130 . As an example and not by way of limitation, the output of the response execution module  232  or the response expansion module  236  may comprise one or more of natural-language strings, speech, actions with parameters, or rendered images or videos that can be displayed in a VR headset or AR smart glasses. As a result, the render output module  242  may determine what tasks to perform based on the output of CU composer to render the response appropriately for displaying on the VR headset or AR smart glasses. For example, the response may be visual-based modality (e.g., an image or a video clip) that can be displayed via the VR headset or AR smart glasses. As another example, the response may be audio signals that can be played by the user via VR headset or AR smart glasses. As yet another example, the response may be augmented-reality data that can be rendered VR headset or AR smart glasses for enhancing user experience. 
     In particular embodiments, the assistant system  140  may have a variety of capabilities including audio cognition, visual cognition, signals intelligence, reasoning, and memories. In particular embodiments, the capability of audio recognition may enable the assistant system  140  to understand a user&#39;s input associated with various domains in different languages, understand a conversation and be able to summarize it, perform on-device audio cognition for complex commands, identify a user by voice, extract topics from a conversation and auto-tag sections of the conversation, enable audio interaction without a wake-word, filter and amplify user voice from ambient noise and conversations, understand which client system  130  (if multiple client systems  130  are in vicinity) a user is talking to. 
     In particular embodiments, the capability of visual cognition may enable the assistant system  140  to perform face detection and tracking, recognize a user, recognize most people of interest in major metropolitan areas at varying angles, recognize majority of interesting objects in the world through a combination of existing machine-learning models and one-shot learning, recognize an interesting moment and auto-capture it, achieve semantic understanding over multiple visual frames across different episodes of time, provide platform support for additional capabilities in people, places, objects recognition, recognize full set of settings and micro-locations including personalized locations, recognize complex activities, recognize complex gestures to control a client system  130 , handle images/videos from egocentric cameras (e.g., with motion, capture angles, resolution, etc.), accomplish similar level of accuracy and speed regarding images with lower resolution, conduct one-shot registration and recognition of people, places, and objects, and perform visual recognition on a client system  130 . 
     In particular embodiments, the assistant system  140  may leverage computer vision techniques to achieve visual cognition. Besides computer vision techniques, the assistant system  140  may explore options that can supplement these techniques to scale up the recognition of objects. In particular embodiments, the assistant system  140  may use supplemental signals such as optical character recognition (OCR) of an object&#39;s labels, GPS signals for places recognition, signals from a user&#39;s client system  130  to identify the user. In particular embodiments, the assistant system  140  may perform general scene recognition (home, work, public space, etc.) to set context for the user and reduce the computer-vision search space to identify top likely objects or people. In particular embodiments, the assistant system  140  may guide users to train the assistant system  140 . For example, crowdsourcing may be used to get users to tag and help the assistant system  140  recognize more objects over time. As another example, users can register their personal objects as part of initial setup when using the assistant system  140 . The assistant system  140  may further allow users to provide positive/negative signals for objects they interact with to train and improve personalized models for them. 
     In particular embodiments, the capability of signals intelligence may enable the assistant system  140  to determine user location, understand date/time, determine family locations, understand users&#39; calendars and future desired locations, integrate richer sound understanding to identify setting/context through sound alone, build signals intelligence models at run time which may be personalized to a user&#39;s individual routines. 
     In particular embodiments, the capability of reasoning may enable the assistant system  140  to have the ability to pick up any previous conversation threads at any point in the future, synthesize all signals to understand micro and personalized context, learn interaction patterns and preferences from users&#39; historical behavior and accurately suggest interactions that they may value, generate highly predictive proactive suggestions based on micro-context understanding, understand what content a user may want to see at what time of a day, understand the changes in a scene and how that may impact the user&#39;s desired content. 
     In particular embodiments, the capabilities of memories may enable the assistant system  140  to remember which social connections a user previously called or interacted with, write into memory and query memory at will (i.e., open dictation and auto tags), extract richer preferences based on prior interactions and long-term learning, remember a user&#39;s life history, extract rich information from egocentric streams of data and auto catalog, and write to memory in structured form to form rich short, episodic and long-term memories. 
       FIG.  3    illustrates an example flow diagram of server-side processes of the assistant system  140 . In particular embodiments, a server-assistant service module  301  may access a request manager  302  upon receiving a user request. In alternative embodiments, the user request may be first processed by the remote ASR module  208  if the user request is based on audio signals. In particular embodiments, the request manager  302  may comprise a context extractor  303  and a conversational understanding object generator (CU object generator)  304 . The context extractor  303  may extract contextual information associated with the user request. The context extractor  303  may also update contextual information based on the assistant application  136  executing on the client system  130 . As an example and not by way of limitation, the update of contextual information may comprise content items are displayed on the client system  130 . As another example and not by way of limitation, the update of contextual information may comprise whether an alarm is set on the client system  130 . As another example and not by way of limitation, the update of contextual information may comprise whether a song is playing on the client system  130 . The CU object generator  304  may generate particular content objects relevant to the user request. The content objects may comprise dialog-session data and features associated with the user request, which may be shared with all the modules of the assistant system  140 . In particular embodiments, the request manager  302  may store the contextual information and the generated content objects in data store  212  which is a particular data store implemented in the assistant system  140 . 
     In particular embodiments, the request manger  302  may send the generated content objects to the remote NLU module  210 . The NLU module  210  may perform a plurality of steps to process the content objects. At step  305 , the NLU module  210  may generate a whitelist for the content objects. In particular embodiments, the whitelist may comprise interpretation data matching the user request. At step  306 , the NLU module  210  may perform a featurization based on the whitelist. At step  307 , the NLU module  210  may perform domain classification/selection on user request based on the features resulted from the featurization to classify the user request into predefined domains. The domain classification/selection results may be further processed based on two related procedures. At step  308   a,  the NLU module  210  may process the domain classification/selection result using an intent classifier. The intent classifier may determine the user&#39;s intent associated with the user request. In particular embodiments, there may be one intent classifier for each domain to determine the most possible intents in a given domain. As an example and not by way of limitation, the intent classifier may be based on a machine-learning model that may take the domain classification/selection result as input and calculate a probability of the input being associated with a particular predefined intent. At step  308   b,  the NLU module  210  may process the domain classification/selection result using a meta-intent classifier. The meta-intent classifier may determine categories that describe the user&#39;s intent. In particular embodiments, intents that are common to multiple domains may be processed by the meta-intent classifier. As an example and not by way of limitation, the meta-intent classifier may be based on a machine-learning model that may take the domain classification/selection result as input and calculate a probability of the input being associated with a particular predefined meta-intent. At step  309   a,  the NLU module  210  may use a slot tagger to annotate one or more slots associated with the user request. In particular embodiments, the slot tagger may annotate the one or more slots for the n-grams of the user request. At step  309   b,  the NLU module  210  may use a meta slot tagger to annotate one or more slots for the classification result from the meta-intent classifier. In particular embodiments, the meta slot tagger may tag generic slots such as references to items (e.g., the first), the type of slot, the value of the slot, etc. As an example and not by way of limitation, a user request may comprise “change 500 dollars in my account to Japanese yen.” The intent classifier may take the user request as input and formulate it into a vector. The intent classifier may then calculate probabilities of the user request being associated with different predefined intents based on a vector comparison between the vector representing the user request and the vectors representing different predefined intents. In a similar manner, the slot tagger may take the user request as input and formulate each word into a vector. The intent classifier may then calculate probabilities of each word being associated with different predefined slots based on a vector comparison between the vector representing the word and the vectors representing different predefined slots. The intent of the user may be classified as “changing money”. The slots of the user request may comprise “500”, “dollars”, “account”, and “Japanese yen”. The meta-intent of the user may be classified as “financial service”. The meta slot may comprise “finance”. 
     In particular embodiments, the NLU module  210  may comprise a semantic information aggregator  310 . The semantic information aggregator  310  may help the NLU module  210  improve the domain classification/selection of the content objects by providing semantic information. In particular embodiments, the semantic information aggregator  310  may aggregate semantic information in the following way. The semantic information aggregator  310  may first retrieve information from a user context engine  315 . In particular embodiments, the user context engine  315  may comprise offline aggregators and an online inference service. The offline aggregators may process a plurality of data associated with the user that are collected from a prior time window. As an example and not by way of limitation, the data may include news feed posts/comments, interactions with news feed posts/comments, search history, etc., that are collected during a predetermined timeframe (e.g., from a prior 90-day window). The processing result may be stored in the user context engine  315  as part of the user profile. The online inference service may analyze the conversational data associated with the user that are received by the assistant system  140  at a current time. The analysis result may be stored in the user context engine  315  also as part of the user profile. In particular embodiments, both the offline aggregators and online inference service may extract personalization features from the plurality of data. The extracted personalization features may be used by other modules of the assistant system  140  to better understand user input. In particular embodiments, the semantic information aggregator  310  may then process the retrieved information, i.e., a user profile, from the user context engine  315  in the following steps. At step  311 , the semantic information aggregator  310  may process the retrieved information from the user context engine  315  based on natural-language processing (NLP). In particular embodiments, the semantic information aggregator  310  may tokenize text by text normalization, extract syntax features from text, and extract semantic features from text based on NLP. The semantic information aggregator  310  may additionally extract features from contextual information, which is accessed from dialog history between a user and the assistant system  140 . The semantic information aggregator  310  may further conduct global word embedding, domain-specific embedding, and/or dynamic embedding based on the contextual information. At step  312 , the processing result may be annotated with entities by an entity tagger. Based on the annotations, the semantic information aggregator  310  may generate dictionaries for the retrieved information at step  313 . In particular embodiments, the dictionaries may comprise global dictionary features which can be updated dynamically offline. At step  314 , the semantic information aggregator  310  may rank the entities tagged by the entity tagger. In particular embodiments, the semantic information aggregator  310  may communicate with different graphs  320  including one or more of the social graph, the knowledge graph, or the concept graph to extract ontology data that is relevant to the retrieved information from the user context engine  315 . In particular embodiments, the semantic information aggregator  310  may aggregate the user profile, the ranked entities, and the information from the graphs  320 . The semantic information aggregator  310  may then provide the aggregated information to the NLU module  210  to facilitate the domain classification/selection. 
     In particular embodiments, the output of the NLU module  210  may be sent to the remote reasoning module  214 . The reasoning module  214  may comprise a co-reference component  325 , an entity resolution component  330 , and a dialog manager  335 . The output of the NLU module  210  may be first received at the co-reference component  325  to interpret references of the content objects associated with the user request. In particular embodiments, the co-reference component  325  may be used to identify an item to which the user request refers. The co-reference component  325  may comprise reference creation  326  and reference resolution  327 . In particular embodiments, the reference creation  326  may create references for entities determined by the NLU module  210 . The reference resolution  327  may resolve these references accurately. As an example and not by way of limitation, a user request may comprise “find me the nearest grocery store and direct me there”. The co-reference component  325  may interpret “there” as “the nearest grocery store”. In particular embodiments, the co-reference component  325  may access the user context engine  315  and the dialog manager  335  when necessary to interpret references with improved accuracy. 
     In particular embodiments, the identified domains, intents, meta-intents, slots, and meta slots, along with the resolved references may be sent to the entity resolution component  330  to resolve relevant entities. The entities may include one or more of a real world entity (from general knowledge base), a user entity (from user memory), a contextual entity (device context/dialog context), or a value resolution (numbers, datetime, etc.). The entity resolution component  330  may execute generic and domain-specific entity resolution. In particular embodiments, the entity resolution component  330  may comprise domain entity resolution  331  and generic entity resolution  332 . The domain entity resolution  331  may resolve the entities by categorizing the slots and meta slots into different domains. In particular embodiments, entities may be resolved based on the ontology data extracted from the graphs  320 . The ontology data may comprise the structural relationship between different slots/meta-slots and domains. The ontology may also comprise information of how the slots/meta-slots may be grouped, related within a hierarchy where the higher level comprises the domain, and subdivided according to similarities and differences. The generic entity resolution  332  may resolve the entities by categorizing the slots and meta slots into different generic topics. In particular embodiments, the resolving may be also based on the ontology data extracted from the graphs  320 . The ontology data may comprise the structural relationship between different slots/meta-slots and generic topics. The ontology may also comprise information of how the slots/meta-slots may be grouped, related within a hierarchy where the higher level comprises the topic, and subdivided according to similarities and differences. As an example and not by way of limitation, in response to the input of an inquiry of the advantages of a particular brand of electric car, the generic entity resolution  332  may resolve the referenced brand of electric car as vehicle and the domain entity resolution  331  may resolve the referenced brand of electric car as electric car. 
     In particular embodiments, the entity resolution component  330  may use different techniques to resolve different types of entities. For real world entities, the entity resolution component  330  may use the knowledge graph to resolve the span to the entities, such as “music track”, “movie”, etc. For user entities, the entity resolution component  330  may use user memory or some agents to resolve the span to user-specific entities, such as “contact”, “reminders”, “relationship”, etc. For contextual entities, the entity resolution component  330  may use the co-reference module  325  to resolve the references to entities in the context, such as “him”, “her”, “the first one”, “the last one”, etc. In addition, the entity resolution component  330  may resolve an entity under the context (device context or dialog context), such as the entity shown on the screen, entity from the last conversation history, etc. For value resolutions, the entity resolution component  330  may resolve the mention to exact value in standardized form, such as numerical value, date time, address, etc. 
     In particular embodiments, the entity resolution component  330  may work on par with the ASR module  208  or the ASR module  216  to perform entity resolution. Taking resolving names as an example, the entity resolution component  330  may work as follows. The entity resolution component  330  may first expand names associated with a user into their normalized text form as well a phonetic consonant representation using a double metaphone algorithm. The entity resolution component  330  may then determine a complete n-best set of candidate transcriptions and run a comprehension process on all transcriptions in parallel. In particular embodiments, each transcription that resolves to the same intent may be collapsed into a single intent. The intent may get a score corresponding to the highest scoring candidate transcription. During the collapse, the entity resolution component  330  may identify various possible text transcriptions associated with each slot, correlated by boundary timing offsets associated with the slot&#39;s transcription. The entity resolution component  330  may extract slot text possibilities from a plurality of (e.g., 1000) candidate transcriptions, regardless of whether they are classified to the same intent. The slots in intents may be thus scored lists of phrases. In particular embodiments, a new or running task which can handle the intent may be identified and deliver the intent. The task may trigger the entity resolution component  330  providing the scored lists of phrases associated with one of its slots and the categories against which it should be resolved. 
     In particular embodiments, when the friend category is specified, the entity resolution component  330  may run every candidate list of terms through the same expansion run at matcher compilation time. Each candidate expansion of the terms may be matched in the precompiled trie matching structure. Matches may be scored using a function that takes the transcribed input, matched form, and friend name. In particular embodiments, when the celebrity/notable person category is specified, the entity resolution component  330  may run parallel searches against the knowledge graph for each candidate set of terms for the slot from the ASR module  208  or ASR module  216 . The entity resolution component  330  may score matches based on matched person popularity and ASR-provided score signal. In particular embodiments, when the memory category is specified, the entity resolution component  330  may perform the same search against user memory. The entity resolution component  330  may crawl backward through user memory and attempt to match each memory (e.g., person recently mentioned in conversation, or seen and recognized via visual signals, etc.) For each person, the entity resolution component  330  may employ matching similarly to how friends are matched (i.e., phoenetic). In particular embodiments, scoring may comprise a temporal decay factor related to how recently the name was mentioned. The entity resolution component  330  may further combine, sort, and dedupe all matches. In particular embodiments, the task may receive the set of candidates. When multiple high scoring candidates are present, the entity resolution component  330  may perform user facilitated disambiguation. 
     In particular embodiments, the entity resolution component  330  may be driven by the task (corresponding to an agent  350 ). This inversion of processing order may make it possible for domain knowledge present in a task to be applied to pre-filter or bias the set of resolution targets when it is obvious and appropriate to do so. As an example and not by way of limitation, for the utterance “who is John?” no clear category is implied in the utterance. Therefore, the entity resolution component  330  may resolve “John” against everything. As another example and not by way of limitation, for the utterance “send a message to John”, the entity resolution component  330  may easily determine “John” refers to a person that one can message. As a result, the entity resolution component  330  may bias the resolution to a friend. As another example and not by way of limitation, for the utterance “what is John&#39;s most famous album?” To resolve “John”, the entity resolution component  330  may first determine the task corresponding to the utterance, which is finding a music album. The entity resolution component  330  may determine that entities related to music albums include singers, producers, and recording studios. Therefore, the entity resolution component  330  may search among these types of entities in a music domain to resolve “John.” 
     In particular embodiments, the output of the entity resolution component  330  may be sent to the dialog manager  335  to advance the flow of the conversation with the user. The dialog manager  335  may be an asynchronous state machine that repeatedly updates the state and selects actions based on the new state. The dialog manager  335  may comprise dialog intent resolution  336  and dialog state tracker  337 . In particular embodiments, the dialog manager  335  may execute the selected actions and then call the dialog state tracker  337  again until the action selected requires a user response, or there are no more actions to execute. Each action selected may depend on the execution result from previous actions. In particular embodiments, the dialog intent resolution  336  may resolve the user intent associated with the current dialog session based on dialog history between the user and the assistant system  140 . The dialog intent resolution  336  may map intents determined by the NLU module  210  to different dialog intents. The dialog intent resolution  336  may further rank dialog intents based on signals from the NLU module  210 , the entity resolution component  330 , and dialog history between the user and the assistant system  140 . In particular embodiments, instead of directly altering the dialog state, the dialog state tracker  337  may be a side-effect free component and generate n-best candidates of dialog state update operators that propose updates to the dialog state. The dialog state tracker  337  may comprise intent resolvers containing logic to handle different types of NLU intent based on the dialog state and generate the operators. In particular embodiments, the logic may be organized by intent handler, such as a disambiguation intent handler to handle the intents when the assistant system  140  asks for disambiguation, a confirmation intent handler that comprises the logic to handle confirmations, etc. Intent resolvers may combine the turn intent together with the dialog state to generate the contextual updates for a conversation with the user. A slot resolution component may then recursively resolve the slots in the update operators with resolution providers including the knowledge graph and domain agents. In particular embodiments, the dialog state tracker  337  may update/rank the dialog state of the current dialog session. As an example and not by way of limitation, the dialog state tracker  337  may update the dialog state as “completed” if the dialog session is over. As another example and not by way of limitation, the dialog state tracker  337  may rank the dialog state based on a priority associated with it. 
     In particular embodiments, the reasoning module  214  may communicate with the remote action execution module  226  and the dialog arbitrator  216 , respectively. In particular embodiments, the dialog manager  335  of the reasoning module  214  may communicate with a task completion component  340  of the action execution module  226  about the dialog intent and associated content objects. In particular embodiments, the task completion module  340  may rank different dialog hypotheses for different dialog intents. The task completion module  340  may comprise an action selector  341 . In alternative embodiments, the action selector  341  may be comprised in the dialog manager  335 . In particular embodiments, the dialog manager  335  may additionally check against dialog policies  345  comprised in the dialog arbitrator  216  regarding the dialog state. In particular embodiments, a dialog policy  345  may comprise a data structure that describes an execution plan of an action by an agent  350 . The dialog policy  345  may comprise a general policy  346  and task policies  347 . In particular embodiments, the general policy  346  may be used for actions that are not specific to individual tasks. The general policy  346  may comprise handling low confidence intents, internal errors, unacceptable user response with retries, skipping or inserting confirmation based on ASR or NLU confidence scores, etc. The general policy  346  may also comprise the logic of ranking dialog state update candidates from the dialog state tracker  337  output and pick the one to update (such as picking the top ranked task intent). In particular embodiments, the assistant system  140  may have a particular interface for the general policy  346 , which allows for consolidating scattered cross-domain policy/business-rules, especial those found in the dialog state tracker  337 , into a function of the action selector  341 . The interface for the general policy  346  may also allow for authoring of self-contained sub-policy units that may be tied to specific situations or clients, e.g., policy functions that may be easily switched on or off based on clients, situation, etc. The interface for the general policy  346  may also allow for providing a layering of policies with back-off, i.e. multiple policy units, with highly specialized policy units that deal with specific situations being backed up by more general policies  346  that apply in wider circumstances. In this context the general policy  346  may alternatively comprise intent or task specific policy. In particular embodiments, a task policy  347  may comprise the logic for action selector  341  based on the task and current state. In particular embodiments, the types of task policies  347  may include one or more of the following types: (1) manually crafted tree-based dialog plans; (2) coded policy that directly implements the interface for generating actions; (3) configurator-specified slot-filling tasks; or (4) machine-learning model based policy learned from data. In particular embodiments, the assistant system  140  may bootstrap new domains with rule-based logic and later refine the task policies  347  with machine-learning models. In particular embodiments, a dialog policy  345  may a tree-based policy, which is a pre-constructed dialog plan. Based on the current dialog state, a dialog policy  345  may choose a node to execute and generate the corresponding actions. As an example and not by way of limitation, the tree-based policy may comprise topic grouping nodes and dialog action (leaf) nodes. 
     In particular embodiments, the action selector  341  may take candidate operators of dialog state and consult the dialog policy  345  to decide what action should be executed. The assistant system  140  may use a hierarchical dialog policy with general policy  346  handling the cross-domain business logic and task policies  347  handles the task/domain specific logic. In particular embodiments, the general policy  346  may pick one operator from the candidate operators to update the dialog state, followed by the selection of a user facing action by a task policy  347 . Once a task is active in the dialog state, the corresponding task policy  347  may be consulted to select right actions. In particular embodiments, both the dialog state tracker  337  and the action selector  341  may not change the dialog state until the selected action is executed. This may allow the assistant system  140  to execute the dialog state tracker  337  and the action selector  341  for processing speculative ASR results and to do n-best ranking with dry runs. In particular embodiments, the action selector  341  may take the dialog state update operators as part of the input to select the dialog action. The execution of the dialog action may generate a set of expectation to instruct the dialog state tracker  337  to handler future turns. In particular embodiments, an expectation may be used to provide context to the dialog state tracker  337  when handling the user input from next turn. As an example and not by way of limitation, slot request dialog action may have the expectation of proving a value for the requested slot. 
     In particular embodiments, the dialog manager  335  may support multi-turn compositional resolution of slot mentions. For a compositional parse from the NLU  210 , the resolver may recursively resolve the nested slots. The dialog manager  335  may additionally support disambiguation for the nested slots. As an example and not by way of limitation, the user request may be “remind me to call Alex”. The resolver may need to know which Alex to call before creating an actionable reminder to-do entity. The resolver may halt the resolution and set the resolution state when further user clarification is necessary for a particular slot. The general policy  346  may examine the resolution state and create corresponding dialog action for user clarification. In dialog state tracker  337 , based on the user request and the last dialog action, the dialog manager may update the nested slot. This capability may allow the assistant system  140  to interact with the user not only to collect missing slot values but also to reduce ambiguity of more complex/ambiguous utterances to complete the task. In particular embodiments, the dialog manager may further support requesting missing slots in a nested intent and multi-intent user requests (e.g., “take this photo and send it to Dad”). In particular embodiments, the dialog manager  335  may support machine-learning models for more robust dialog experience. As an example and not by way of limitation, the dialog state tracker  337  may use neural network based models (or any other suitable machine-learning models) to model belief over task hypotheses. As another example and not by way of limitation, for action selector  341 , highest priority policy units may comprise white-list/black-list overrides, which may have to occur by design; middle priority units may comprise machine-learning models designed for action selection; and lower priority units may comprise rule-based fallbacks when the machine-learning models elect not to handle a situation. In particular embodiments, machine-learning model based general policy unit may help the assistant system  140  reduce redundant disambiguation or confirmation steps, thereby reducing the number of turns to execute the user request. 
     In particular embodiments, the action execution module  226  may call different agents  350  for task execution. An agent  350  may select among registered content providers to complete the action. The data structure may be constructed by the dialog manager  335  based on an intent and one or more slots associated with the intent. A dialog policy  345  may further comprise multiple goals related to each other through logical operators. In particular embodiments, a goal may be an outcome of a portion of the dialog policy and it may be constructed by the dialog manager  335 . A goal may be represented by an identifier (e.g., string) with one or more named arguments, which parameterize the goal. As an example and not by way of limitation, a goal with its associated goal argument may be represented as {confirm_artist, args: {artist: “Madonna”}}. In particular embodiments, a dialog policy may be based on a tree-structured representation, in which goals are mapped to leaves of the tree. In particular embodiments, the dialog manager  335  may execute a dialog policy  345  to determine the next action to carry out. The dialog policies  345  may comprise generic policy  346  and domain specific policies  347 , both of which may guide how to select the next system action based on the dialog state. In particular embodiments, the task completion component  340  of the action execution module  226  may communicate with dialog policies  345  comprised in the dialog arbitrator  216  to obtain the guidance of the next system action. In particular embodiments, the action selection component  341  may therefore select an action based on the dialog intent, the associated content objects, and the guidance from dialog policies  345 . 
     In particular embodiments, the output of the action execution module  226  may be sent to the remote response execution module  232 . Specifically, the output of the task completion component  340  of the action execution module  226  may be sent to the CU composer  355  of the response execution module  226 . In alternative embodiments, the selected action may require one or more agents  350  to be involved. As a result, the task completion module  340  may inform the agents  350  about the selected action. Meanwhile, the dialog manager  335  may receive an instruction to update the dialog state. As an example and not by way of limitation, the update may comprise awaiting agents&#39;  350  response. In particular embodiments, the CU composer  355  may generate a communication content for the user using a natural-language generation (NLG) module  356  based on the output of the task completion module  340 . In particular embodiments, the NLG module  356  may use different language models and/or language templates to generate natural language outputs. The generation of natural language outputs may be application specific. The generation of natural language outputs may be also personalized for each user. The CU composer  355  may also determine a modality of the generated communication content using the UI payload generator  357 . Since the generated communication content may be considered as a response to the user request, the CU composer  355  may additionally rank the generated communication content using a response ranker  358 . As an example and not by way of limitation, the ranking may indicate the priority of the response. In particular embodiments, the CU composer  355  may comprise a natural-language synthesis (NLS) module that may be separate from the NLG module  356 . The NLS module may specify attributes of the synthesized speech generated by the CU composer  355 , including gender, volume, pace, style, or register, in order to customize the response for a particular user, task, or agent. The NLS module may tune language synthesis without engaging the implementation of associated tasks. More information on customizing natural-language generation may be found in U.S. patent application Ser. No. 15/966455, filed 30 Apr. 2018, which is incorporated by reference. 
     In particular embodiments, the response execution module  232  may perform different tasks based on the output of the CU composer  355 . These tasks may include writing (i.e., storing/updating) the dialog state  361  retrieved from data store  212  and generating responses  362 . In particular embodiments, the output of CU composer  355  may comprise one or more of natural-language strings, speech, actions with parameters, or rendered images or videos that can be displayed in a VR headset or AR smart glass. As a result, the response execution module  232  may determine what tasks to perform based on the output of CU composer  355 . In particular embodiments, the generated response and the communication content may be sent to the local render output module  242  by the response execution module  232 . In alternative embodiments, the output of the CU composer  355  may be additionally sent to the remote TTS module  238  if the determined modality of the communication content is audio. The speech generated by the TTS module  238  and the response generated by the response execution module  232  may be then sent to the render output module  242 . 
       FIG.  4    illustrates an example flow diagram of processing a user input by the assistant system  140 . As an example and not by way of limitation, the user input may be based on audio signals. In particular embodiments, a mic array  402  of the client system  130  may receive the audio signals (e.g., speech). The audio signals may be transmitted to a process loop  404  in a format of audio frames. In particular embodiments, the process loop  404  may send the audio frames for voice activity detection (VAD)  406  and wake-on-voice (WoV) detection  408 . The detection results may be returned to the process loop  404 . If the WoV detection  408  indicates the user wants to invoke the assistant system  140 , the audio frames together with the VAD  406  result may be sent to an encode unit  410  to generate encoded audio data. After encoding, the encoded audio data may be sent to an encrypt unit  412  for privacy and security purpose, followed by a link unit  414  and decrypt unit  416 . After decryption, the audio data may be sent to a mic driver  418 , which may further transmit the audio data to an audio service module  420 . In alternative embodiments, the user input may be received at a wireless device (e.g., Bluetooth device) paired with the client system  130 . Correspondingly, the audio data may be sent from a wireless-device driver  422  (e.g., Bluetooth driver) to the audio service module  420 . In particular embodiments, the audio service module  420  may determine that the user input can be fulfilled by an application executing on the client system  130 . Accordingly, the audio service module  420  may send the user input to a real-time communication (RTC) module  424 . The RTC module  424  may deliver audio packets to a video or audio communication system (e.g., VOIP or video call). The RTC module  424  may call a relevant application (App)  426  to execute tasks related to the user input. 
     In particular embodiments, the audio service module  420  may determine that the user is requesting assistance that needs the assistant system  140  to respond. Accordingly, the audio service module  420  may inform the client-assistant service module  426 . In particular embodiments, the client-assistant service module  426  may communicate with the assistant orchestrator  206 . The assistant orchestrator  206  may determine whether to use client-side processes or server-side processes to respond to the user input. In particular embodiments, the assistant orchestrator  206  may determine to use client-side processes and inform the client-assistant service module  426  about such decision. As a result, the client-assistant service module  426  may call relevant modules to respond to the user input. 
     In particular embodiments, the client-assistant service module  426  may use the local ASR module  216  to analyze the user input. The ASR module  216  may comprise a grapheme-to-phoneme (G2P) model, a pronunciation learning model, a personalized language model (PLM), an end-pointing model, and a personalized acoustic model. In particular embodiments, the client-assistant service module  426  may further use the local NLU module  218  to understand the user input. The NLU module  218  may comprise a named entity resolution (NER) component and a contextual session-based NLU component. In particular embodiments, the client-assistant service module  426  may use an intent broker  428  to analyze the user&#39;s intent. To be accurate about the user&#39;s intent, the intent broker  428  may access an entity store  430  comprising entities associated with the user and the world. In alternative embodiments, the user input may be submitted via an application  432  executing on the client system  130 . In this case, an input manager  434  may receive the user input and analyze it by an application environment (App Env) module  436 . The analysis result may be sent to the application  432  which may further send the analysis result to the ASR module  216  and NLU module  218 . In alternative embodiments, the user input may be directly submitted to the client-assistant service module  426  via an assistant application  438  executing on the client system  130 . Then the client-assistant service module  426  may perform similar procedures based on modules as aforementioned, i.e., the ASR module  216 , the NLU module  218 , and the intent broker  428 . 
     In particular embodiments, the assistant orchestrator  206  may determine to user server-side process. Accordingly, the assistant orchestrator  206  may send the user input to one or more computing systems that host different modules of the assistant system  140 . In particular embodiments, a server-assistant service module  301  may receive the user input from the assistant orchestrator  206 . The server-assistant service module  301  may instruct the remote ASR module  208  to analyze the audio data of the user input. The ASR module  208  may comprise a grapheme-to-phoneme (G2P) model, a pronunciation learning model, a personalized language model (PLM), an end-pointing model, and a personalized acoustic model. In particular embodiments, the server-assistant service module  301  may further instruct the remote NLU module  210  to understand the user input. In particular embodiments, the server-assistant service module  301  may call the remote reasoning model  214  to process the output from the ASR module  208  and the NLU module  210 . In particular embodiments, the reasoning model  214  may perform entity resolution and dialog optimization. In particular embodiments, the output of the reasoning model  314  may be sent to the agent  350  for executing one or more relevant tasks. 
     In particular embodiments, the agent  350  may access an ontology module  440  to accurately understand the result from entity resolution and dialog optimization so that it can execute relevant tasks accurately. The ontology module  440  may provide ontology data associated with a plurality of predefined domains, intents, and slots. The ontology data may also comprise the structural relationship between different slots and domains. The ontology data may further comprise information of how the slots may be grouped, related within a hierarchy where the higher level comprises the domain, and subdivided according to similarities and differences. The ontology data may also comprise information of how the slots may be grouped, related within a hierarchy where the higher level comprises the topic, and subdivided according to similarities and differences. Once the tasks are executed, the agent  350  may return the execution results together with a task completion indication to the reasoning module  214 . 
     The embodiments disclosed herein may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured content (e.g., real-world photographs). The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may be associated with applications, products, accessories, services, or some combination thereof, that are, e.g., used to create content in an artificial reality and/or used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HIVID) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers. 
     Generating Context-Aware Rendering of Media Contents 
     In particular embodiments, the assistant system  140  may adaptively determine the most appropriate way to render content (e.g., notifications) to a user in real time on various client devices (e.g., smart glasses, AR glasses, VR headset, etc.) to prioritize relevant information for the user without distraction. As an example and not by way of limitation, for a client device that supports multimodal outputs, the content may be rendered visually, as sound, or as speech, and a variety of ways may exist within each of those modalities. To effectively determine how to render content, the assistant system  140  may use various information including relevance of content, priority of content, user engagement, and user context from the user context engine  315 . Among others, attention context and physio-social context may be two main types of user context that help with such determinization. Attention context may reveal how focused a user is on the assistant system  140  or the client device with respect to the world. Physio-social context may reveal what the user is currently engaged with, e.g., alone, around other people but not interacting with them, and interacting with other people, etc. The user context engine  315  may further map the relevance of content, priority of content, user engagement, and user context into different levels, with each of them corresponding to a different design of how the content should be rendered to the user. Although this disclosure describes rendering particular content by particular systems in a particular manner, this disclosure contemplates rending any suitable content by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may receive a media content for delivery to a first user. The media content may be associated with a priority level. The assistant system  140  may then access context information associated with the first user. In particular embodiments, the context information may be determined based on one or more multimodal signals from a client device associated with the first user. The assistant system  140  may also determine a delivery level for the media content based on the priority level of the media content and the context information. In particular embodiments, the assistant system  140  may further instruct the client device to present a notification associated with the media content to the first user. The notification may be rendered in one or more modalities determined based on the delivery level for the media content. 
     A user may not want too many notifications of media content or deal with too many settings for these notifications. In addition, there may be too much burden on the user if the user has to define notification behaviors. As an example and not by way of limitation, a user may get over 70 notifications everyday across different services, which may be overwhelming and annoying if all of them are delivered to the user via an interrupting modality such as audio. Therefore, the assistant system  140  may deliver the right information and the right amount of information at the right time instead of all the time to avoid overwhelming the user with irrelevant notifications. The notifications may be actionable in the moment on a client device. In particular embodiments, the assistant system  140  may determine whether the received media content should be delivered to the first user based on the priority level associated with the media content. As an example and not by way of limitation, the priority level may be high/highly relevant, moderate/moderately relevant, or low/irrelevant. As a result, the assistant system  140  may have a technical advantage of enabling the user to access the most suitable and relevant information without overwhelming the user based on their priority and relevance. 
       FIG.  5    illustrates example correlations between relevance/priority and immediate attention requirement for different example notifications. As illustrated in  FIG.  5   , these notifications may be grouped into targeted alerts  502  (promotional), social alerts  504  (engagement) and personal alerts  506  (deterministic/essential). As an example and not by way of limitation, “breaking news story”  508 , “BBC, The Daily Show and others posted new videos”  510 , “check out the Oculus Quest and more hot deals nearby”  512 , “price drop from item you viewed”  514 , “the Oculus Quest you viewed is now $50 less”  516 , “a seller you follow, recently added an item”  518 , “browse more furniture listings in your area”  520 , “your fundraiser is over”  522 , “you have an event invitation waiting a response”  524 , “a friend marked themselves as safe”  526 , “you have an unopened saved item”  528 , and “a close friend posted a status update”  530  may be targeted alerts  502 . Among others, “breaking news story”  508  may be the least relevant and does not require immediate attention at all. “You have an unopened saved item”  524  and “a close friend posted a status update”  530  may be moderately relevant and more relevant than the other example notifications in the targeted alerts  502 . “Your fundraiser is over”  522  may require more immediate attention than the other example notifications in the targeted alerts  502 . The correlation between relevance/priority and immediate attention requirement for other example targeted alerts  502  may be observed intuitively from  FIG.  5   . As another example and not by way of limitation, “live video from page you follow”  532 , “a gamer you follow is streaming live”  534 , “let people know if you&#39;ve sold your item”  536 , “person followed what you sell on Marketplace”  538 , “friends birthday is today”  540 , and “you were added as a page admin”  542  may be social alerts  504 . Among others, “live video from page you follow”  532  and “a gamer you follow is streaming live”  534  may be the least relevant whereas “you were added as a page admin”  542  may be the most relevant. Both “friends birthday is today”  540  and “you were added as a page admin”  542  may be relevant and require moderately immediate attention. “Person followed what you sell on Marketplace”  538  may be moderately relevant and require the most immediate attention. The correlation between relevance/priority and immediate attention requirement for other example social alerts  504  may be observed intuitively from  FIG.  5   . As another example and not by way of limitation, “status change for your job application”  544 , “page has a new message”  546 , “account was accessed from another device”  548 , “message about your listing”  550 , “friend commented on your photo”  552 , and “someone reacted to a post”  554  may be personal alerts  506 . Among others, “status change for your job application”  544  may be moderately relevant and require immediate attention. “Account was accessed from another device”  548  may be highly relevant (most relevant compared to other personal alerts  506 ) and require immediate attention (more than other personal alerts  506 ). The correlation between relevance/priority and immediate attention requirement for other example personal alerts may be observed intuitively from  FIG.  5   . Although this disclosure describes particular correlations in a particular manner, this disclosure contemplates any suitable correlation in any suitable manner. 
     In particular embodiments, the media content may comprise one or more of text, an image, a video clip, an audio clip, or a voice utterance. The media content may originate from a second user. As an example and not by way of limitation, the media content may be an incoming message from the second user. As another example and not by way of limitation, the media content may be a post posted by the second user. As yet another example and not by way of limitation, the media content may be an image in which the second user tagged the first user. In particular embodiments, the priority level associated with the media content may be determined based on a degree of separation between the first user and the second user within an online social network. Taking notifications as an example, high-priority notifications may include direct messages from high-priority contacts (e.g., contacts with a high social-graph affinity/coefficient, favorite contacts, or frequent/recent contacts). Moderate-priority notifications may include direct messages from low coefficient contacts, non-messages in group chats (e.g., admin messages or reactions), direct messages from low-priority contacts, follow-up messages in a conversation thread, direct messages from known contacts, incoming calls from known contacts, messages in group chats, or calls from number that have been contacted recently. Irrelevant notifications may include admin messages, direct messages from unknown contacts, or calls from unknown numbers that have never been contacted. Although this disclosure describes particular priority levels of particular contents in a particular manner, this disclosure contemplates any suitable priority level of any suitable content in any suitable manner. 
     In particular embodiments, the assistant system  140  may filter media contents and their notifications and adaptively determine how the filtered results should be delivered to the user. The assistant system  140  may use different types of filters such as low filter, moderate filter, and high filter. In particular embodiments, the assistant system  140  may use the low filter to make everything available, e.g., all media content and their associated notifications may come through. In particular embodiments, when using the moderate filter, favorites/whitelist contacts may get full media content delivery while other media content and notifications may get minimal platform specific delivery. With moderate filter, no low-priority media content and notifications may be delivered. In particular embodiments, the assistant system  140  may use the high filter to deliver only media contents and notifications from whitelist contacts. As a result, media contents and notifications that have significantly low priority may be not delivered to the user by the assistant system  140 . In particular embodiments, the assistant system  140  may dynamically determine what filter to apply on the media contents and notifications. As an example and not by way of limitation, a user may set a default filter, but the assistant system  140  may dynamically alter the filter based on user context. For example, if the user has set a low filter but the user is in a conversation with someone, the assistant system  140  may alter the filter to a moderate filter. As another example, if the user has set a low filter but the user is driving, the assistant system  140  may alter the filter to a high filter. Applying different types of filters on media contents and notifications may be an effective solution for addressing the technical challenge of determining what media contents and notifications to deliver to a user as these filters reflect different levels of priorities and relevance of the media contents and notifications with respect to the user. Although this disclosure describes using particular filters by particular systems in a particular manner, this disclosure contemplates using any suitable filter by any suitable system in any suitable manner. 
     In particular embodiments, a user or the assistant system  140  may determine different modes for the delivery of media content and notifications. These modes may correspond to everything on, lightly filtered, moderately filtered, highly filtered, or everything off. As an example and not by way of limitation, if the user sets the mode as everything on, the assistant system  140  may use no filter to let every media content and notification be delivered to the user. As another example and not by way of limitation, if the user sets the mode as lightly filtered, the assistant system  140  may use a low filter to only limit notifications that are overly distracting or unimportant (e.g., calls from unknown numbers or marketing messages). The user may get every notification from his/her network so that the user is always up to date. As another example and not by way of limitation, if the user sets the mode as moderately filtered, the assistant system  140  may use a moderate filter to balance the number of notifications the user gets to make sure the user is getting relevant content from his/her closest connections at the right time, which is a good balance of prioritization and filtering to help the user stay connected and present. For example, with the moderate filter, messages from favorites or whitelist contacts may get full message readout. Other messages may get minimal platform specific sound and announcement. In addition, no low-priority notifications may be delivered to the user. As yet another example and not by way of limitation, if the mode is highly filtered, the assistant system  140  may use a combination of signals to make sure the user is only getting the most important notifications at the right time from the people who matter most. For example, the assistant system  140  may only deliver notifications from whitelist or system/hardware level notifications for things like battery. As yet another example and not by way of limitation, if the user switches to a do-not-disturb (DND) mode (i.e., everything off), the assistant system  140  may have no media content or notification provided to the user. Although this disclosure describes using particular mode by particular systems in a particular manner, this disclosure contemplates using any suitable mode by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may use a user&#39;s distraction level for the delivery of media content and notifications. The distraction level may be idle, occupied, or highly distracted. In particular embodiments, “idle” may indicate the user is not engaging with any activity that requires attention. As an example and not by way of limitation, when the user is sitting in the living room drinking coffee, the distraction level may be considered idle. As another example and not by way of limitation, when the user is just listening to music the distraction level may be also considered idle. In particular embodiments, the assistant system  140  may use a low filter to have media content and notifications delivered to the user when the distraction level is idle. In particular embodiments, when the user is engaging with activities that require moderate attention, the distraction level may be occupied. As an example and not by way of limitation, when the user is browsing the newsfeed of a social-networking application, the distraction level may be occupied. As another example and not by way of limitation, when the user is watching a movie, the distraction level may be also occupied. In particular embodiments, the assistant system  140  may use a moderate filter to filter media contents and notifications when the distraction level is occupied. In particular embodiments, when the user is engaging with activities that require full attention, the distraction level may be highly distracted. As an example and not by way of limitation, when the user is in a business meeting, the distraction level may be highly distracted. As another example and not by way of limitation, when the user is taking an exam, the distraction level may be highly distracted. In particular embodiments, the assistant system  140  may use a high filter to filter media contents and notifications when the distraction level is highly distracted. Using a user&#39;s distraction level may be an effective solution for addressing the technical challenge of determining what media contents and notifications to deliver to a user as the user&#39;s distraction level may help determine what types of filters to use to filter media contents and notifications. Although this disclosure describes using particular distraction levels by particular systems in a particular manner, this disclosure contemplates using any suitable distraction level by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may use a user&#39;s attitude for the delivery of media contents and notifications. The user&#39;s attitude may be receptive, indifferent, or averse. In particular embodiments, the receptive attitude may indicate the user is willing to receive media contents and notifications. Correspondingly, the assistant system  140  may use a low filter to filter media contents and notifications. In particular embodiments, the indifferent attitude may indicate the user is without interest or concern for media contents and notifications or not caring if he/she receives media contents and notifications. Correspondingly, the assistant system  140  may use a moderate filter to have only certain media contents and notifications delivered to the user. In particular embodiments, the averse attitude may indicate the user is having a clear dislike of receiving media contents and notifications or strongly opposed to receiving them. Correspondingly, the assistant system  140  may use a high filter to have no or only few media contents and notifications with high priority delivered to the user. Using a user&#39;s attitude may be an effective solution for addressing the technical challenge of determining what media contents and notifications to deliver to a user as the user&#39;s attitude may help determine what types of filters to use to filter media contents and notifications. Although this disclosure describes using particular attitude by particular systems in a particular manner, this disclosure contemplates using any suitable attitude by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may use time information for the delivery of media contents and notifications. The time information may indicate whether it is appropriate, neutral, or inappropriate to deliver a media content and notification. As an example and not by way of limitation, when a user is walking in a park, the timing may be appropriate. As another example and not by way of limitation, when the user is reading a book, the timing may be neutral. As yet another example and not by way of limitation, when the user is sleeping, the timing may be inappropriate. In particular embodiments, the assistant system  140  may use a low filter to filter media content and notifications if the timing is appropriate. The assistant system  140  may use a moderate filter when the timing is neutral. In particular embodiments, the assistant system  140  may use a high filter if the timing is inappropriate. Although this disclosure describes using particular time information by particular systems in a particular manner, this disclosure contemplates using any suitable time information by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may combine different factors as aforementioned when determining what media contents and notifications should be delivered to a user. As an example and not by way of limitation, if there is a high-priority notification and the user is in a receptive state (i.e., not otherwise distracted), the assistant system  140  may apply a low filter. But if the user is distracted, the assistant system  140  may apply a high filter. As another example and not by way of limitation, for a moderate-priority notification where the user is distracted, the assistant system  140  may apply a high filter. Although this disclosure describes determining particular delivery by particular systems in a particular manner, this disclosure contemplates determining any suitable delivery by any suitable system in any suitable manner. 
     In particular embodiments, the client device may be a pair of smart glasses, a virtual-reality device, or an augmented-reality device. On all client devices, the assistant system  140  may be multimodal, representing itself with its voice, visuals, sounds, haptics, lights, etc. In particular embodiments, the one or more modalities may comprise one or more of a text modality, an imagery modality, a video modality, an XR modality, a sound modality, a voice modality, or a light modality. XR stands for extended reality, which is a term referring to all real-and-virtual combined environments and human-machine interactions generated by computer technology and wearables, where the ‘X’ represents a variable for any current or future spatial computing technologies. XR may include representative forms such as augmented reality (AR), mixed reality (MR) and virtual reality (VR) and the areas interpolated among them. Within those modalities there may be a variety of ways to render the media content and notification. Although this disclosure describes particular client devices in a particular manner, this disclosure contemplates using any suitable client device in any suitable manner. 
       FIG.  6    illustrates an example notification matrix based on different combinations of filters and priorities. As illustrated in  FIG.  6   , for a low-priority media content  605 , the assistant system  140  may use a low filter  610 , which may result in a notification based on a combination of voice, light, and sound. For a moderate-priority media content  615 , the assistant system  140  may use a low filter  610 , which may result in a notification based on a combination of verbose voice, light, and sound. In particular embodiments, verbose voice indicates using voice when possible to provide more informative updates and notifications. For a high-priority media content  620 , the assistant system  140  may use a low filter  610 , which may result in a notification based on a combination of verbose voice, light, and sound. For a low-priority media content  605 , the assistant system  140  may use a moderate filter  625 , which may result in a notification based on either light or sound. For a moderate-priority media content  615 , the assistant system  140  may use a moderate filter  625 , which may result in a notification based on a combination of voice, light, and sound. For a high-priority media content  620 , the assistant system  140  may use a moderate filter  625 , which may result in a notification based on a combination of verbose voice, light, and sound. For a low-priority media content  605 , the assistant system  140  may use a high filter  630 , which may result in no notification. For a moderate-priority media content  615 , the assistant system  140  may use a high filter  630 , which may result in a notification based on either light or sound. For a high-priority media content  620 , the assistant system  140  may use a high filter  630 , which may result in a notification based on a combination of voice, light, and sound. If the mode is do-not-disturb (DND)  635 , there may be no notification no matter what priority the media content has. Although this disclosure describes particular combinations in a particular manner, this disclosure contemplates any suitable combination in any suitable manner. 
     In particular embodiments, the assistant system  140  may determine a delivery level for the media content based on the priority level of the media content and the context information. The delivery level may reflect the right blend of multiple modalities (e.g., audio and visual) for the media contents and notifications to serve to users. Determining when each of these modalities is appropriate to present to a user may be a consistent technical challenge, particularly when deciding how much of each modality to make use of at a given time. In particular embodiments, the assistant system  140  may use context information to determine how a notification should be rendered to make sure such notification is contextually sensitive and not interrupting or distracting a user from real life or other high-priority activities. Using context information to determine how a notification should be rendered may be an effective solution for addressing the technical challenge of determining when each of these modalities is appropriate to present to a user, particularly when deciding how much of each modality to make use of at a given time as the assistant system  140  may make sure such notification is contextually sensitive and not interrupting or distracting a user from real life or other high-priority activities. Although this disclosure describes determining particular delivery levels by particular systems in a particular manner, this disclosure contemplates determining any suitable delivery level by any suitable system in any suitable manner. 
     In particular embodiments, the context information associated with the first user may comprise attention-context information. The attention-context information may indicate the user&#39;s current engagement with the client device and how much attention the user is spending on tasks outside the client device. As an example and not by way of limitation, if the attention-context information indicates the user is looking at the display/screen of the client device, the assistant system  140  may render the media content and notification visually. As another example and not by way of limitation, if the attention-context information indicates the user is looking away from the client device (e.g., jogging), the assistant system  140  may render the media content and notification auditorily to not obscure the user&#39;s visual field. As yet another example and not by way of limitation, if the attention-context information indicates the user is driving, the assistant system  140  may interact with the user by sound only when the user wants to send a message. In particular embodiments, the assistant system  140  may determine the attention-context information based on optical signals from the client device. As an example and not by way of limitation, the optical signals may comprise signals captured by a camera of the client device, which may cover the user&#39;s face. The assistant system  140  may then perform eye tracking based on such signals to determine how much attention the user is spending on the client device or on tasks outside the client device. As another example and not by way of limitation, the optical signals may comprise videos captured by the camera of the client device, which may include the user&#39;s whole body. The assistant system  140  may then perform action recognition based on the videos to determine whether the user is focusing on the client device or something else. Although this disclosure describes particular context information in a particular manner, this disclosure contemplates any suitable context information by any suitable system in any suitable manner. 
     In particular embodiments, the context information associated with the first user may comprise physio-social context information. There may be three types of physio-social context information, i.e., “alone”, “around others without interaction”, and “interaction with others”. As an example and not by way of limitation, if a user is in a conversation with a friend, the user may not want the assistant system  140  speaking up to tell him/her that he/she got a text message from his/her partner, for which the assistant system  140  may render the media content and notification visually because the user shouldn&#39;t be distracted from listening to the other person. As another example and not by way of limitation, if the user is at a party but not talking to anyone right now, the assistant system  140  may render media content and notification as a mixture of audio output and visual output. In particular embodiments, the assistant system  140  may determine the physio-social context information based on human detection around the first user. As an example and not by way of limitation, the human detection may be based on one or more of facial recognition or speech recognition, which may tell if the user is around others and/or interacting with them. In particular embodiments, the assistant system  104  may consider both attention-context information and physio-social context information when determining how to render media contents and notifications. As an example and not by way of limitation, if the user is at home alone reading a book via a client device, the attention-context information may indicate the user is engaged with the client device whereas the physio-social context information is “alone”. Therefore, the assistant system  140  may render media content and notification in audio only because the user&#39;s view shouldn&#39;t be obscured, and the user is not listening to others. Determining when each of the modalities for media contents and notifications is appropriate to present to the user may result in a technical advantage for the assistant system  140  that the user may feel connected to the assistant system  140  but also engaged with the world. Although this disclosure describes particular context information in a particular manner, this disclosure contemplates any suitable context information in any suitable manner. 
     In particular embodiments, the assistant system  140  may determine a delivery level for the media content and notification. The delivery level may comprise one or more of a visual-only level, a visual-forward level, an auditory-forward level, or an auditory-only level. In particular embodiments, the user context engine (UCE)  315  may take in signals detected by a client device, determine the user context based on the signals, and then map the user context to one of the aforementioned delivery levels. In particular embodiments, each delivery level may correspond to a specific design of how to render media content and notification. These designs may be characterized by an inverse relationship between visual rendering and audio rendering, i.e., as audio rendering increases, visual rendering decreases, and vice-versa. Although this disclosure describes particular delivery levels in a particular manner, this disclosure contemplates any suitable delivery level in any suitable manner. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Delivery-level variation based on both  
               
               
                 physio-social context and focus level. 
               
            
           
           
               
               
            
               
                   
                 Context 
               
            
           
           
               
               
               
               
            
               
                 Focus 
                 Alone 
                 Around others 
                 With others 
               
               
                   
               
               
                 Very high 
                 Voice Only 
                 — 
                 Visual Only 
               
               
                 High 
                 Voice-Forward 
                 Voice-Forward/  
                 Visual-Forward 
               
               
                   
                   
                 Visual-Forward 
                   
               
               
                 Medium 
                 Voice-Forward 
                 Voice-Forward/ 
                 Visual-Forward 
               
               
                   
                   
                 Visual-Forward 
                   
               
               
                 Low 
                 Visual-Forward 
                 Visual-Forward/ 
                 Voice-Forward 
               
               
                   
                   
                 Voice-Forward 
                   
               
               
                 Very low 
                 Visual-Forward 
                 Visual-Forward/ 
                 Voice-Forward 
               
               
                   
                   
                 Voice-Forward 
               
               
                   
               
            
           
         
       
     
     Table 1 illustrates an example delivery-level variation based on both physio-social context and focus level. In particular embodiments, the assistant system  140  may combine the physio-social context information, i.e., “alone”, “around others without interaction”, and “interaction with others” with user focus levels to determine the delivery level for the media content and notification. If the user is alone and the focus level is high, the delivery level may be voice-forward. If the user is alone and the focus level is medium, the delivery level may be voice-forward. If the user is alone and the focus level is low, the delivery level may be visual-forward. If the user is alone and the focus level is very low, the delivery level may be visual-forward. If the user is around others without interaction and the focus level is high, the delivery level may be voice-forward or visual-forward. If the user is around others without interaction and the focus level is medium, the delivery level may be voice-forward or visual-forward. If the user is around others without interaction and the focus level is low, the delivery level may be visual-forward or voice-forward. If the user is around others without interaction and the focus level is very low, the delivery level may be visual-forward or voice-forward. If the user is interacting with others and the focus level is very high, the delivery level may be visual only. If the user is interacting with others and the focus level is high, the delivery level may be visual-forward. If the user is interacting with others and the focus level is medium, the delivery level may be visual-forward. If the user is interacting with others and the focus level is low, the delivery level may be voice-forward. If the user is interacting with others and the focus level is very low, the delivery level may be voice-forward. In particular embodiments, voice only and visual only may be judiciously applied such that most of the time the user is moving between a voice-forward level and visual-forward experience. As user focus level decreases when alone, the delivery level may shift towards visual-forward. As user focus level decreases when interacting with others, the delivery level may shift away from visual-forward/visual only towards voice-forward. Determining the delivery level based on both physio-social context and focus level may be an effective solution for addressing the technical challenge of determining a delivery level for the media content and notification as they may capture the user&#39;s engagement with the surroundings and user activities. Although this disclosure describes particular variations of particular delivery levels in a particular manner, this disclosure contemplates any suitable variation of any suitable delivery level in any suitable manner. 
     In particular embodiments, the assistant system  140  may determine, based on the delivery level for the media content, an intensity for each of the one or more modalities. The notification may be rendered in the one or more modalities corresponding to their respective intensities. In particular embodiments, the intensity may comprise one or more of a low intensity, a moderate intensity, or a high intensity. As an example and not by way of limitation, low intensity may correspond to the platform notification sound (e.g., a simple ping sound), LED signals, or phone haptics. As another example and not by way of limitation, moderate intensity may correspond to platform notification sound plus a lightweight voice prompt, platform notification sound plus light, or a lightweight voice prompt. As another example and not by way of limitation, high intensity may correspond to a full message/notification readout plus sound and light, or a companion device visuals. In particular embodiments, the companion device may be a device paired with the client device the user is primarily using (e.g., a smart watch may be a companion device for a smart phone). Although this disclosure describes particular intensity in a particular manner, this disclosure contemplates any suitable intensity in any suitable manner. 
       FIG.  7    illustrates an example hierarchy of intensity of notification  700 . As illustrates in  FIG.  7   , light  705  may have the lowest intensity. Sound  710  may have higher intensity than light. Voice  715  may be more intense than sound. Voice plus light and sound  720  may have higher intensity than voice  715 . The combination of verbose voice, light and sound  725  may have higher intensity. In particular embodiments, light  705  and sound  710  may both be settings turned on by default. Additional settings may affect verbosity, such as message readout. Although this disclosure describes particular hierarchy of particular intensity in a particular manner, this disclosure contemplates any suitable hierarchy of any suitable intensity in any suitable manner. 
       FIG.  8    illustrates example variance of intensity for notifications. As illustrated in  FIG.  8   , in one embodiment, the lowest intensity of notification may be based on light  705  or sound  710  only. As the intensity increases, the notification may be based on both light  705  and sound  710 . As the intensity continues increasing, the notification may be based on lightweight voice. As the intensity further increases, the notification may be based on both voice  715  and sound  710 . The highest intensity of notification may be based on a combination of voice, sound, and light  720 . In another embodiment, the lowest intensity of notification may be based on light  705 . As the intensity increases, the notification may be based on sound  710 . As the intensity continues increasing, the notification may be based on voice  715 . As the intensity further increases, the notification may be based on both voice  715  and sound  710 . The highest intensity of notification may be based on a combination of voice, sound, and light  720 . In yet another embodiment, the lowest intensity of notification may be based on light  705 . As the intensity increases, the notification may be based on sound  710 . As the intensity continues increasing, the notification may be based on voice  715 . As the intensity further increases, the notification may be based on voice  715  and sound  710 . The highest intensity of notification may be based on a combination of verbose voice, sound, and light  725 . In yet another embodiment, the lowest intensity of notification may be based on light  705 . As the intensity increases, the notification may be based on sound  710 . As the intensity continues increasing, the notification may be based on voice  715 . As the intensity continues increasing, the notification may be based on both voice  715  and sound  710 . As the intensity further increases, the notification may be based on a mixture of minimal voice, light and sound. The highest intensity of notification may be based on a maximum power. In yet another embodiment, the lowest intensity of notification may be based on light  705 . As the intensity increases, the notification may be based on sound  710 . As the intensity continues increasing, the notification may be based on voice  715 . As the intensity further increases, the notification may be based on a combination of voice, light and sound  720 . The highest intensity of notification may be based on a combination of verbose voice, sound, and light  725 . Although this disclosure describes particular variance of particular intensity in a particular manner, this disclosure contemplates any suitable variance of any suitable intensity in any suitable manner. 
     In particular embodiments, the assistant system  140  may combine different factors among user&#39;s engagement, degree of attention, user context, and relevance of content, to determine the intensity of a notification. In particular embodiments, the assistant system  140  may combine two or more of the priority of the contact, the priority level of media content, and the distraction level to determine the rendering of the notifications. As an example and not by way of limitation, for a high-relevance content from a high-priority contact, the assistant system  140  may determine a moderate notification for rendering. As another example and not by way of limitation, for a high-relevance content with the user at low distraction level, the assistant system  140  may determine a moderate notification for rendering. As yet another example and not by way of limitation, for a content from a high-priority contact with the user at low distraction level, the assistant system  140  may determine a moderate notification for rendering. As yet another example and not by way of limitation, for a high-relevance content from a high-priority contact with the user at low distraction level, the assistant system  140  may determine a heavy notification for rendering. As yet another example and not by way of limitation, for a low-relevance content from a low-priority contact, the assistant system  140  may determine a moderate notification for rendering. As yet another example and not by way of limitation, for a low-relevance content with the user at high distraction level, the assistant system  140  may determine a lightweight notification for rendering. As yet another example and not by way of limitation, for a content from a low-priority contact with the user at high distraction level, the assistant system  140  may determine a lightweight notification for rendering. As yet another example and not by way of limitation, for a low-relevance content from a low-priority contact with the user at high distraction level, the assistant system  140  may determine to render no notification. Determining the intensity based on a combination of different factors among user&#39;s engagement, degree of attention, user context, and relevance of content may be an effective solution for addressing the technical challenge of determining the intensity for each of the modalities used to render the media content and notification, as these factors may reflect the user&#39;s engagement with the surroundings and user activities and the importance of the media contents and notifications to the user. Although this disclosure describes determining particular intensity by particular systems in a particular manner, this disclosure contemplates determining any suitable intensity by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may combine two or more of the priority of the contact, the priority level of media content, and the user attitude to determine the rendering of the notifications. As an example and not by way of limitation, for a high-priority content from a favorite contact, the assistant system  140  may determine a moderate notification for rendering. As another example and not by way of limitation, for a high-priority content with the user at high receptivity, the assistant system  140  may determine a moderate notification for rendering. As yet another example and not by way of limitation, for a content from a favorite contact with the user at high receptivity, the assistant system  140  may determine a moderate notification for rendering. As yet another example and not by way of limitation, for a high-priority content from a favorite contact with the user at high receptivity, the assistant system  140  may determine a heavy notification for rendering. Although this disclosure describes determining particular rendering of particular notifications by particular systems in a particular manner, this disclosure contemplates determining any suitable rendering of any suitable notification by any suitable system in any suitable manner. 
       FIG.  9    illustrates an example visualization of how to deliver notifications based on a combination of factors. In particular embodiments, the assistant system  140  may use user&#39;s current engagement with the client device, how much attention the user is expending on tasks outside the client device, user context, and relevance/priority of the content (e.g., notifications) to select different filters and different intensities. As illustrated in  FIG.  9   , the assistant system  140  may combine priority level, distraction level, and user&#39;s attitude to determine what filter and intensity to use. When the media contents have high relevance/priority  910  and the user is at low distraction or high receptivity  920 , all notifications unless some limited by user settings on the client device may be delivered to the user. When the media contents have low relevance/priority  930  and the user is at low distraction or high receptivity  920 , the corresponding notifications may be suppressed or be delivered to the user in a lightweight way. When the media contents have high relevance/priority  910  and the user is at low distraction or high receptivity  940 , all notifications unless some limited by user settings on the client device may be delivered to the user. When the media contents have high relevance/priority  910  and the user is at low distraction or high receptivity  920 , all notifications unless some limited by user settings on the client device may be delivered to the user. Although this disclosure describes determining particular delivery by particular systems in a particular manner, this disclosure contemplates determining any suitable delivery by any suitable system in any suitable manner. 
     In particular embodiments, the assistant system  140  may vary the intensity, verbosity, etc. of how the media content and notification should be rendered based on the user&#39;s engagement, degree of attention, user context, and relevance of content. As an example and not by way of limitation, the assistant system  140  may apply a low filter for a high-priority media content when the user is in a receptive state (i.e., not otherwise distracted), for which the delivery of the notification may include verbose voice, light, and sound. But if the user is distracted, the assistant system  140  may apply a high filter and deliver the notification in normal and/or limited voice combined with light and sound. As another example and not by way of limitation, the assistant system  140  may apply a high filter for a moderate-priority media content when the user is distracted, for which the delivery of the notification may be based on light and sound but no voice. In particular embodiments, light notifications may be based on various colors depending on the notifications (e.g., messages may be a blue light, alerts may be a red light, etc.). Some media contents may have such low priority that no notifications of these media contents may be provided to users on their main client devices (but these notifications may be still available on companion devices, e.g., in lock screen). In particular embodiments, the assistant system  140  may also add haptics or other notifications from paired devices (e.g., smart watches) as an alternative or additional way to provide notifications of media contents. Although this disclosure describes determining particular delivery by particular systems in a particular manner, this disclosure contemplates determining any suitable delivery by any suitable system in any suitable manner. 
       FIG.  10    illustrates an example visualization of relevance, distraction level, and receptivity of different scenarios. As illustrated in  FIG.  10   , an “@mention in group chat while cooking at home” may have high relevance  910 , low distraction or high receptivity  920 . A “reply to a message while scrolling a newsfeed” may have high relevance  910  (which may be slightly lower than the “@mention in group chat while cooking at home”), low distraction  920  (which may be slightly lower than the “@mention in group chat while cooking at home”) or high receptivity  920  (which may be slightly higher than the “@mention in group chat while cooking at home”). A “direct message from a non-priority contact while walking the dog” may have moderate relevance, moderate distraction or receptivity. A “direct message from a priority contact while driving” may have high relevance  910 , high distraction or low receptivity  940 . A “call from a priority contact while at work” may have high relevance  910  (which may be slightly lower than the “direct message from a priority contact while driving”), moderate distraction or receptivity. A “call from a non-priority contact while on a run” may have high relevance  910  (which may be slightly lower than the “call from a priority contact while at work”), high distraction  940  (which may be slightly lower than the “direct message from a priority contact while driving”) or low receptivity  940  (which may be slightly lower than the “direct message from a priority contact while driving”). 
     As illustrated in  FIG.  10   , “reactions to a message in a group chat while giving a presentation” may have moderate relevance, high distraction or low receptivity  940 . A “direct message from a low-coefficient contact while in a call” may have low relevance  930 , moderate distraction or receptivity. “Marketing messages from a business that is not a favorite while giving a presentation” may have low relevance  930 , high distraction or low receptivity  940 . A “call from an unknown number (likely a spam) while on public transit” may have low relevance  930 , low distraction or high receptivity  920 . An “admin message in a non-priority group chat while watching TV” may have low relevance  930  (which may be slightly higher than the “call from an unknown number while on public transit”), low distraction  920  (which may be slightly higher than the “call from an unknown number while on public transit”) or high receptivity  920  (which may be slightly higher than the “call from an unknown number while on public transit”). 
     In particular embodiments, the delivery level may characterize the blend of modalities that the media content and notification served by the assistant system  140 . In particular embodiments, the visual-only level may correspond to rending the notification only in a visual modality. The visual modality may comprise one or more of a text modality, an imagery modality, a video modality, an XR modality, or a light modality. The visual-only may address instances where the user either can&#39;t, or doesn&#39;t need to, limit exposure to visual content. The visual-only level may be particularly effective in situations where the user&#39;s audio focus is at capacity, e.g., they may be in a noisy environment, listening to music, or focusing on a conversation. Although this disclosure describes particular visual modalities in a particular manner, this disclosure contemplates any suitable visual modality in any suitable manner. 
     In particular embodiments, the visual-forward level may correspond to rending the notification in at least a first modality and a second modality. The first modality may be associated with a high intensity and the second modality may be associated with a moderate intensity. As an example and not by way of limitation, the first modality may comprise one or more of a text modality, an imagery modality, a video modality, an XR modality, or a light modality, and the second modality may comprise one or more of a sound modality or a voice modality. At the visual-forward level, the user may be expected to be visually attending to the assistant system  140  in order to use it. Confirmations for actions to be taken by the assistant system  140  may occur visually rather than audibly. As an example and not by way of limitation, if the client device is an AR headset, it is likely that the visual-forward level may be where most interactions with the client device take place. In other words, in situations where the user&#39;s visual focus is not at capacity but is likely focused on the AR display, and their physio-social contexts are low-stakes. Although this disclosure describes particular visual levels in a particular manner, this disclosure contemplates any suitable visual level in any suitable manner. 
     In particular embodiments, the auditory-forward level may correspond to rending the notification in at least a first modality and a second modality. The first modality may be associated with a moderate intensity and the second modality may be associated with a high intensity. As an example and not by way of limitation, the first modality may comprise one or more of a text modality, an imagery modality, a video modality, an XR modality, or a light modality, and the second modality may comprise one or more of a sound modality or a voice modality. The auditory-forward level may be where some visual elements are introduced, but where all tasks within the experience may be accomplished by voice. This means that the user may not rely on the visuals, which is particularly useful in situations where the UCE  315  has less-than-certain confidence that the user is able to visually attend to the client device&#39;s outputs. Although this disclosure describes particular auditory levels in a particular manner, this disclosure contemplates any suitable auditory level in any suitable manner. 
     In particular embodiments, the auditory-only level may correspond to rendering the notification only in an auditory modality. The auditory modality may comprise one or more of a sound modality or a voice modality. At the auditory-only level, there may be no visuals but only audio signals. As an example and not by way of limitation, this may look and feel like a “headphone experience”, where the user is not looking at anything. This may be useful in situations where the user&#39;s visual focus is outside of the client device or the user&#39;s device experience is at capacity. As can be seen, the aforementioned delivery levels reflect a relationship between media content and notifications the user consumes visually versus audibly. When the user&#39;s auditory focus is at capacity, the assistant system  140  may present media content and notifications visually. When the user&#39;s visual focus is at capacity, the assistant system  140  may present media content and notifications auditorily. Although this disclosure describes particular auditory levels in a particular manner, this disclosure contemplates any suitable auditory level in any suitable manner. 
     In particular embodiments, the assistant system  140  may further consider device modes when determining how to render the media content and notification. Device modes may be vert, user-selected, and surfaced as settings that are manually enabled or disabled. A device mode may help assure a user of a client device that the client device is behaving in a specific way. Device modes may be turned on or off in settings of client devices and may be already defined. A user may select more than one device mode at a time. As an example and not by way of limitation, device modes may be labeled as “privacy”, “do-not-disturb”, “airplane”, and “audio-only”. Users may have their devices set to “privacy” while still being served media contents and notifications by the assistant system  140 . Similarly, users may have their devices set to “airplane” while still being able to interact with the assistant system  140  via on-device models and/or WiFi signal. In particular embodiments, the assistant system  140  may also consider device settings when determining how to render the media content and notification. A device setting may be a user-selected, device-centric setting, including device modes, but also including if the user has turned the volume all the way down. In particular embodiments, the assistant system  140  may consider device state when determining how, and if, a client device does, or doesn&#39;t serve the media content and notification. Although this disclosure describes particular device modes in a particular manner, this disclosure contemplates any suitable device mode in any suitable manner. 
     When the device setting is “no sensor” and the device mode is “privacy”, both visuals and voice may be reduced when rendering media content and notifications. When the device setting is “no notifications” and the device mode is “do-not-disturb”, both visuals and voice may be reduced when rendering media content and notifications. When the device setting is “no data” and the device mode is “airplane”, both visuals and voice may be reduced when rendering media content and notifications. When the device setting is “no visuals” and the device mode is “audio only”, there may be no visuals but only voice when rendering media content and notifications. 
     In particular embodiments, the assistant system  140  may use augment states to determine the degree to which the interactive dynamic content in the world is hydrated and engaged with. As an example and not by way of limitation, there may be two main augment states in which an augment can function, including “glinted” and “interactive”. In particular embodiments, “glinted” may be a minimized state imposed upon it by the shell whereas “interactive” may allow the user to engage with it in its full functionality. In particular embodiments, there may be a correlation between augment states and delivery levels. When the augment state is glinted, the engagement may be voice-forward. When the augment state is interactive, the engagement may be visual-forward. The delivery level may be considered as existing in parallel with the “size” of the augment. The larger the augment or closer to the augment the user is, the more visual-forward the augment may become. The smaller the augment, or further away the user is from it, the more voice-forward the augment may become. Although this disclosure describes particular augment states in a particular manner, this disclosure contemplates any suitable augment state in any suitable manner. 
     Table 2 illustrates example renderings of media contents and notifications based on delivery level and multiple additional factors. When the device setting is “display off”, only media content and notifications that are voice-only level may be rendered. There may be no visuals but only voice and the augment state may be audio only. When the device setting is “sound off”, only media content and notifications that are visual-only level may be rendered. There may be no voice but only visuals and the augment state may be audio off. When the device setting is not “display off” or “sound off”, media content and notifications at other delivery levels may be rendered. As an example and not by way of limitation, media content and notifications at voice-forward level may be rendered with some visuals and mostly voice and the augment state may be glint. As another example and not by way of limitation, media content and notifications at visual-forward level may be rendered with mostly visuals and some voice and the augment state may be interactive. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Renderings based on delivery level and multiple additional factors 
               
            
           
           
               
               
               
               
               
            
               
                 Device Setting 
                 Delivery Level 
                 Visual 
                 Audio 
                 Augment State 
               
               
                   
               
               
                 Display Off 
                 Voice-Forward 
                 None 
                 Only 
                 Audio Only 
               
               
                   
                 Voice-Forward 
                 Some 
                 Most 
                 Glint 
               
               
                   
                 Visual-Forward 
                 Most 
                 Some 
                 Interactive 
               
               
                 Sound Off 
                 Visual-Forward 
                 Only 
                 None 
                 Audio Off 
               
               
                   
               
            
           
         
       
     
       FIG.  11    illustrates an example notification of an incoming message while a user is running. A user  1105  wearing smart glasses  1110  may be running. There may be an incoming message for the user  1105 . As the user  1105  is running, the assistant system  140  may determine audio as the suitable modality to deliver the notification of the incoming message to the user as audio may be least interruptive to the user&#39;s  1105  running activity. The notification  1115  may be “your Mom sent you message saying she locked herself out of her house and needs you to bring the spare key to her.” 
       FIG.  12    illustrates an example notification of a reminder while a user is at a library. A user  1205  wearing smart glasses  1210  may be at a library. A reminder  1215  for the user  1205  to send her report may be activated. As the user  1205  is at the library, the assistant system  140  may determine visual as the suitable modality to deliver the reminder  1215  as people should keep quiet at a library. The assistant system  140  may present the reminder  1215  on the display  1220  of the smart glasses  1210 . The reminder  1215  may be “please remind to send your work report by 3 pm today”. 
       FIG.  13    illustrates an example notification of a social-media post while a user is at a party. A user  1305  wearing smart glasses  1310  may be at a party talking with other people. The user&#39;s  1305  friend Kyle may have posted on a social media that he lost his dog. The assistant system  140  may determine to notify the user  1305  about this post. As the user  1305  is interacting with other people, the assistant system  140  may determine visual as the suitable modality to notify the user  1305  as visual may be the least interruptive modality to the user&#39;s  1305  ongoing activity. Accordingly, the assistant system  140  may present the notification  1315  together with Kyle&#39;s post  1320  on the display  1325  of the smart glasses  1310 . Kyle&#39;s post  1320  may be “lost my dog” with a dog picture. The notification  1315  may be “Kyle posted that his dog Coby got lost.” 
       FIG.  14    illustrates an example notification of new messages while a user is at a party. A user  1405  wearing smart glasses  1410  may be at a party but not interacting with other people. There may be new messages for the user  1405 . The assistant system  140  may determine to notify the user  1405  about them. As the user  1405  is not interacting with other people, the assistant system  140  may determine to notify the user  1405  by both audio and light. Accordingly, the assistant system  140  may present the notification  1415  as a readout, e.g., “new messages”, together with a light flashing  1420  on the smart glasses  1410 . 
       FIG.  15    illustrates an example notification of an incoming message while a user is playing games. A user  1505  wearing VR headset  1510  may be at home playing a VR sports game. There may be an incoming message and the assistant system  140  may determine to notify the user  1505  about it since it is important. To not interrupt the user&#39;s  1505  game, the assistant system  140  may determine sound and light as the modality to deliver the notification. For example, there may be a beep sound  1515  and also a light flashing  1520  on the VR headset  1210 . 
       FIG.  16    illustrates an example notification of traffic situation while a user is getting ready for work. A user  1605  wearing smart glasses  1610  may be at home getting ready for work. There may be car accidents on the user&#39;s  1605  route to work and the assistant system  140  may determine to notify the user  1605  about that. The assistant system  140  may deliver the notification  1615  as a readout, which may be “there are several car accidents on your route to work.” The assistant system  140  may simultaneously present the images  1620  of the car accidents on the display  1625  of the smart glasses. 
       FIG.  17    illustrates an example method  1700  for generating context-aware notifications. The method may begin at step  1710 , where the assistant system  140  may receive a media content for delivery to a first user, wherein the media content is associated with a priority level, comprises one or more of text, an image, a video clip, an audio clip, or a voice utterance, and originates from a second user, wherein the priority level associated with the media content is determined based on a degree of separation between the first user and the second user within an online social network, and wherein the client device is a pair of smart glasses, a virtual-reality device, or an augmented-reality device. At step  1720 , the assistant system  140  may determine whether the received media content should be delivered to the first user based on the priority level associated with the media content. At step  1730 , the assistant system  140  may access context information associated with the first user, wherein the context information is determined based on one or more multimodal signals from a client device associated with the first user, wherein the context information associated with the first user comprises attention-context information, and the method further comprising determining the attention-context information based on optical signals from the client device, wherein the context information associated with the first user comprises physio-social context information, and the method further comprising determining the physio-social context information based on human detection around the first user, wherein the human detection is based on one or more of facial recognition or speech recognition. At step  1740 , the assistant system  140  may determine a delivery level for the media content based on the priority level of the media content and the context information, wherein the delivery level comprises one or more of a visual-only level, a visual-forward level, an auditory-forward level, or an auditory-only level, wherein the visual-only level corresponds to rending the notification only in a visual modality comprising one or more of a text modality, an imagery modality, a video modality, an XR modality, or a light modality, wherein the visual-forward level corresponds to rending the notification in at least a first modality and a second modality, the first modality being associated with a high intensity and the second modality being associated with a moderate intensity, wherein the auditory-forward level corresponds to rending the notification in at least a first modality and a second modality, the first modality being associated with a moderate intensity and the second modality being associated with a high intensity, wherein the auditory-only level corresponds to rending the notification only in an auditory modality comprising one or more of a sound modality or a voice modality, wherein the first modality comprises one or more of a text modality, an imagery modality, a video modality, an XR modality, or a light modality, and wherein the second modality comprises one or more of a sound modality or a voice modality. At step  1750 , the assistant system  140  may instruct the client device to present a notification associated with the media content to the first user, wherein the notification is rendered in one or more modalities determined based on the delivery level for the media content, wherein the one or more modalities comprise one or more of a text modality, an imagery modality, a video modality, an XR modality, a sound modality, a voice modality, or a light modality. Particular embodiments may repeat one or more steps of the method of  FIG.  17   , where appropriate. Although this disclosure describes and illustrates particular steps of the method of  FIG.  17    as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG.  17    occurring in any suitable order. Moreover, although this disclosure describes and illustrates an example method for generating context-aware notifications including the particular steps of the method of  FIG.  17   , this disclosure contemplates any suitable method for generating context-aware notifications including any suitable steps, which may include all, some, or none of the steps of the method of  FIG.  17   , where appropriate. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG.  17   , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG.  17   . 
     Social Graphs 
       FIG.  18    illustrates an example social graph  1800 . In particular embodiments, the social-networking system  160  may store one or more social graphs  1800  in one or more data stores. In particular embodiments, the social graph  1800  may include multiple nodes—which may include multiple user nodes  1802  or multiple concept nodes  1804 —and multiple edges  1806  connecting the nodes. Each node may be associated with a unique entity (i.e., user or concept), each of which may have a unique identifier (ID), such as a unique number or username. The example social graph  1800  illustrated in  FIG.  18    is shown, for didactic purposes, in a two-dimensional visual map representation. In particular embodiments, a social-networking system  160 , a client system  130 , an assistant system  140 , or a third-party system  170  may access the social graph  1800  and related social-graph information for suitable applications. The nodes and edges of the social graph  1800  may be stored as data objects, for example, in a data store (such as a social-graph database). Such a data store may include one or more searchable or queryable indexes of nodes or edges of the social graph  1800 . 
     In particular embodiments, a user node  1802  may correspond to a user of the social-networking system  160  or the assistant system  140 . As an example and not by way of limitation, a user may be an individual (human user), an entity (e.g., an enterprise, business, or third-party application), or a group (e.g., of individuals or entities) that interacts or communicates with or over the social-networking system  160  or the assistant system  140 . In particular embodiments, when a user registers for an account with the social-networking system  160 , the social-networking system  160  may create a user node  1802  corresponding to the user, and store the user node  1802  in one or more data stores. Users and user nodes  1802  described herein may, where appropriate, refer to registered users and user nodes  1802  associated with registered users. In addition or as an alternative, users and user nodes  1802  described herein may, where appropriate, refer to users that have not registered with the social-networking system  160 . In particular embodiments, a user node  1802  may be associated with information provided by a user or information gathered by various systems, including the social-networking system  160 . As an example and not by way of limitation, a user may provide his or her name, profile picture, contact information, birth date, sex, marital status, family status, employment, education background, preferences, interests, or other demographic information. In particular embodiments, a user node  1802  may be associated with one or more data objects corresponding to information associated with a user. In particular embodiments, a user node  1802  may correspond to one or more web interfaces. 
     In particular embodiments, a concept node  1804  may correspond to a concept. As an example and not by way of limitation, a concept may correspond to a place (such as, for example, a movie theater, restaurant, landmark, or city); a website (such as, for example, a website associated with the social-networking system  160  or a third-party website associated with a web-application server); an entity (such as, for example, a person, business, group, sports team, or celebrity); a resource (such as, for example, an audio file, video file, digital photo, text file, structured document, or application) which may be located within the social-networking system  160  or on an external server, such as a web-application server; real or intellectual property (such as, for example, a sculpture, painting, movie, game, song, idea, photograph, or written work); a game; an activity; an idea or theory; another suitable concept; or two or more such concepts. A concept node  1804  may be associated with information of a concept provided by a user or information gathered by various systems, including the social-networking system  160  and the assistant system  140 . As an example and not by way of limitation, information of a concept may include a name or a title; one or more images (e.g., an image of the cover page of a book); a location (e.g., an address or a geographical location); a website (which may be associated with a URL); contact information (e.g., a phone number or an email address); other suitable concept information; or any suitable combination of such information. In particular embodiments, a concept node  1804  may be associated with one or more data objects corresponding to information associated with concept node  1804 . In particular embodiments, a concept node  1804  may correspond to one or more web interfaces. 
     In particular embodiments, a node in the social graph  1800  may represent or be represented by a web interface (which may be referred to as a “profile interface”). Profile interfaces may be hosted by or accessible to the social-networking system  160  or the assistant system  140 . Profile interfaces may also be hosted on third-party websites associated with a third-party system  170 . As an example and not by way of limitation, a profile interface corresponding to a particular external web interface may be the particular external web interface and the profile interface may correspond to a particular concept node  1804 . Profile interfaces may be viewable by all or a selected subset of other users. As an example and not by way of limitation, a user node  1802  may have a corresponding user-profile interface in which the corresponding user may add content, make declarations, or otherwise express himself or herself. As another example and not by way of limitation, a concept node  1804  may have a corresponding concept-profile interface in which one or more users may add content, make declarations, or express themselves, particularly in relation to the concept corresponding to concept node  1804 . 
     In particular embodiments, a concept node  1804  may represent a third-party web interface or resource hosted by a third-party system  170 . The third-party web interface or resource may include, among other elements, content, a selectable or other icon, or other inter-actable object representing an action or activity. As an example and not by way of limitation, a third-party web interface may include a selectable icon such as “like,” “check-in,” “eat,” “recommend,” or another suitable action or activity. A user viewing the third-party web interface may perform an action by selecting one of the icons (e.g., “check-in”), causing a client system  130  to send to the social-networking system  160  a message indicating the user&#39;s action. In response to the message, the social-networking system  160  may create an edge (e.g., a check-in-type edge) between a user node  1802  corresponding to the user and a concept node  1804  corresponding to the third-party web interface or resource and store edge  1806  in one or more data stores. 
     In particular embodiments, a pair of nodes in the social graph  1800  may be connected to each other by one or more edges  1806 . An edge  1806  connecting a pair of nodes may represent a relationship between the pair of nodes. In particular embodiments, an edge  1806  may include or represent one or more data objects or attributes corresponding to the relationship between a pair of nodes. As an example and not by way of limitation, a first user may indicate that a second user is a “friend” of the first user. In response to this indication, the social-networking system  160  may send a “friend request” to the second user. If the second user confirms the “friend request,” the social-networking system  160  may create an edge  1806  connecting the first user&#39;s user node  1802  to the second user&#39;s user node  1802  in the social graph  1800  and store edge  1806  as social-graph information in one or more of data stores  164 . In the example of  FIG.  18   , the social graph  1800  includes an edge  1806  indicating a friend relation between user nodes  1802  of user “A” and user “B” and an edge indicating a friend relation between user nodes  1802  of user “C” and user “B.” Although this disclosure describes or illustrates particular edges  1806  with particular attributes connecting particular user nodes  1802 , this disclosure contemplates any suitable edges  1806  with any suitable attributes connecting user nodes  1802 . As an example and not by way of limitation, an edge  1806  may represent a friendship, family relationship, business or employment relationship, fan relationship (including, e.g., liking, etc.), follower relationship, visitor relationship (including, e.g., accessing, viewing, checking-in, sharing, etc.), subscriber relationship, superior/subordinate relationship, reciprocal relationship, non-reciprocal relationship, another suitable type of relationship, or two or more such relationships. Moreover, although this disclosure generally describes nodes as being connected, this disclosure also describes users or concepts as being connected. Herein, references to users or concepts being connected may, where appropriate, refer to the nodes corresponding to those users or concepts being connected in the social graph  1800  by one or more edges  1806 . The degree of separation between two objects represented by two nodes, respectively, is a count of edges in a shortest path connecting the two nodes in the social graph  1800 . As an example and not by way of limitation, in the social graph  1800 , the user node  1802  of user “C” is connected to the user node  1802  of user “A” via multiple paths including, for example, a first path directly passing through the user node  1802  of user “B,” a second path passing through the concept node  1804  of company “Alme” and the user node  1802  of user “D,” and a third path passing through the user nodes  1802  and concept nodes  1804  representing school “SchoolName,” user “G,” company “CompanyName,” and user “D.” User “C” and user “A” have a degree of separation of two because the shortest path connecting their corresponding nodes (i.e., the first path) includes two edges  1806 . 
     In particular embodiments, an edge  1806  between a user node  1802  and a concept node  1804  may represent a particular action or activity performed by a user associated with user node  1802  toward a concept associated with a concept node  1804 . As an example and not by way of limitation, as illustrated in  FIG.  18   , a user may “like,” “attended,” “played,” “listened,” “cooked,” “worked at,” or “read” a concept, each of which may correspond to an edge type or subtype. A concept-profile interface corresponding to a concept node  1804  may include, for example, a selectable “check in” icon (such as, for example, a clickable “check in” icon) or a selectable “add to favorites” icon. Similarly, after a user clicks these icons, the social-networking system  160  may create a “favorite” edge or a “check in” edge in response to a user&#39;s action corresponding to a respective action. As another example and not by way of limitation, a user (user “C”) may listen to a particular song (“SongName”) using a particular application (a third-party online music application). In this case, the social-networking system  160  may create a “listened” edge  1806  and a “used” edge (as illustrated in  FIG.  18   ) between user nodes  1802  corresponding to the user and concept nodes  1804  corresponding to the song and application to indicate that the user listened to the song and used the application. Moreover, the social-networking system  160  may create a “played” edge  1806  (as illustrated in  FIG.  18   ) between concept nodes  1804  corresponding to the song and the application to indicate that the particular song was played by the particular application. In this case, “played” edge  1806  corresponds to an action performed by an external application (the third-party online music application) on an external audio file (the song “SongName”). Although this disclosure describes particular edges  1806  with particular attributes connecting user nodes  1802  and concept nodes  1804 , this disclosure contemplates any suitable edges  1806  with any suitable attributes connecting user nodes  1802  and concept nodes  1804 . Moreover, although this disclosure describes edges between a user node  1802  and a concept node  1804  representing a single relationship, this disclosure contemplates edges between a user node  1802  and a concept node  1804  representing one or more relationships. As an example and not by way of limitation, an edge  1806  may represent both that a user likes and has used at a particular concept. Alternatively, another edge  1806  may represent each type of relationship (or multiples of a single relationship) between a user node  1802  and a concept node  1804  (as illustrated in  FIG.  18    between user node  1802  for user “E” and concept node  1804  for “online music application”). 
     In particular embodiments, the social-networking system  160  may create an edge  1806  between a user node  1802  and a concept node  1804  in the social graph  1800 . As an example and not by way of limitation, a user viewing a concept-profile interface (such as, for example, by using a web browser or a special-purpose application hosted by the user&#39;s client system  130 ) may indicate that he or she likes the concept represented by the concept node  1804  by clicking or selecting a “Like” icon, which may cause the user&#39;s client system  130  to send to the social-networking system  160  a message indicating the user&#39;s liking of the concept associated with the concept-profile interface. In response to the message, the social-networking system  160  may create an edge  1806  between user node  1802  associated with the user and concept node  1804 , as illustrated by “like” edge  1806  between the user and concept node  1804 . In particular embodiments, the social-networking system  160  may store an edge  1806  in one or more data stores. In particular embodiments, an edge  1806  may be automatically formed by the social-networking system  160  in response to a particular user action. As an example and not by way of limitation, if a first user uploads a picture, reads a book, watches a movie, or listens to a song, an edge  1806  may be formed between user node  1802  corresponding to the first user and concept nodes  1804  corresponding to those concepts. Although this disclosure describes forming particular edges  1806  in particular manners, this disclosure contemplates forming any suitable edges  1806  in any suitable manner. 
     Vector Spaces and Embeddings 
       FIG.  19    illustrates an example view of a vector space  1900 . In particular embodiments, an object or an n-gram may be represented in a d-dimensional vector space, where d denotes any suitable number of dimensions. Although the vector space  1900  is illustrated as a three-dimensional space, this is for illustrative purposes only, as the vector space  1900  may be of any suitable dimension. In particular embodiments, an n-gram may be represented in the vector space  1900  as a vector referred to as a term embedding. Each vector may comprise coordinates corresponding to a particular point in the vector space  1900  (i.e., the terminal point of the vector). As an example and not by way of limitation, vectors  1910 ,  1920 , and  1930  may be represented as points in the vector space  1900 , as illustrated in  FIG.  19   . An n-gram may be mapped to a respective vector representation. As an example and not by way of limitation, n-grams t 1  and t 2  may be mapped to vectors   and   in the vector space  1900 , respectively, by applying a function   defined by a dictionary, such that  = (t 1 ) and  = (t 2 ). As another example and not by way of limitation, a dictionary trained to map text to a vector representation may be utilized, or such a dictionary may be itself generated via training. As another example and not by way of limitation, a word-embeddings model may be used to map an n-gram to a vector representation in the vector space  1900 . In particular embodiments, an n-gram may be mapped to a vector representation in the vector space  1900  by using a machine leaning model (e.g., a neural network). The machine learning model may have been trained using a sequence of training data (e.g., a corpus of objects each comprising n-grams). 
     In particular embodiments, an object may be represented in the vector space  1900  as a vector referred to as a feature vector or an object embedding. As an example and not by way of limitation, objects e 1  and e 2  may be mapped to vectors   and   in the vector space  1900 , respectively, by applying a function  , such that  =  (e 1 ) and  =  (e 2 ). In particular embodiments, an object may be mapped to a vector based on one or more properties, attributes, or features of the object, relationships of the object with other objects, or any other suitable information associated with the object. As an example and not by way of limitation, a function may map objects to vectors by feature extraction, which may start from an initial set of measured data and build derived values (e.g., features). As an example and not by way of limitation, an object comprising a video or an image may be mapped to a vector by using an algorithm to detect or isolate various desired portions or shapes of the object. Features used to calculate the vector may be based on information obtained from edge detection, corner detection, blob detection, ridge detection, scale-invariant feature transformation, edge direction, changing intensity, autocorrelation, motion detection, optical flow, thresholding, blob extraction, template matching, Hough transformation (e.g., lines, circles, ellipses, arbitrary shapes), or any other suitable information. As another example and not by way of limitation, an object comprising audio data may be mapped to a vector based on features such as a spectral slope, a tonality coefficient, an audio spectrum centroid, an audio spectrum envelope, a Mel-frequency cepstrum, or any other suitable information. In particular embodiments, when an object has data that is either too large to be efficiently processed or comprises redundant data, a function   may map the object to a vector using a transformed reduced set of features (e.g., feature selection). In particular embodiments, a function   may map an object e to a vector  (e) based on one or more n-grams associated with object e. Although this disclosure describes representing an n-gram or an object in a vector space in a particular manner, this disclosure contemplates representing an n-gram or an object in a vector space in any suitable manner. 
     In particular embodiments, the social-networking system  160  may calculate a similarity metric of vectors in vector space  1900 . A similarity metric may be a cosine similarity, a Minkowski distance, a Mahalanobis distance, a Jaccard similarity coefficient, or any suitable similarity metric. As an example and not by way of limitation, a similarity metric of   and   may be a cosine similarity 
     
       
         
           
             
               
                 
                   
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                    
                   
                     
                       v 
                       1 
                     
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                    
                 
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     As another example and not by way of limitation, a similarity metric of   and   may be a Euclidean distance ∥ − ∥. A similarity metric of two vectors may represent how similar the two objects or n-grams corresponding to the two vectors, respectively, are to one another, as measured by the distance between the two vectors in the vector space  1900 . As an example and not by way of limitation, vector  1910  and vector  1920  may correspond to objects that are more similar to one another than the objects corresponding to vector  1910  and vector  1930 , based on the distance between the respective vectors. Although this disclosure describes calculating a similarity metric between vectors in a particular manner, this disclosure contemplates calculating a similarity metric between vectors in any suitable manner. 
     More information on vector spaces, embeddings, feature vectors, and similarity metrics may be found in U.S. patent application Ser. No. 14/949436, filed 23 Nov. 2015, U.S. patent application Ser. No. 15/286315, filed 5 Oct. 2016, and U.S. patent application Ser. No. 15/365789, filed 30 Nov. 2016, each of which is incorporated by reference. 
     Artificial Neural Networks 
       FIG.  20    illustrates an example artificial neural network (“ANN”)  2000 . In particular embodiments, an ANN may refer to a computational model comprising one or more nodes. Example ANN  2000  may comprise an input layer  2010 , hidden layers  2020 ,  2030 ,  2040 , and an output layer  2050 . Each layer of the ANN  2000  may comprise one or more nodes, such as a node  2005  or a node  2015 . In particular embodiments, each node of an ANN may be connected to another node of the ANN. As an example and not by way of limitation, each node of the input layer  2010  may be connected to one of more nodes of the hidden layer  2020 . In particular embodiments, one or more nodes may be a bias node (e.g., a node in a layer that is not connected to and does not receive input from any node in a previous layer). In particular embodiments, each node in each layer may be connected to one or more nodes of a previous or subsequent layer. Although  FIG.  20    depicts a particular ANN with a particular number of layers, a particular number of nodes, and particular connections between nodes, this disclosure contemplates any suitable ANN with any suitable number of layers, any suitable number of nodes, and any suitable connections between nodes. As an example and not by way of limitation, although  FIG.  20    depicts a connection between each node of the input layer  2010  and each node of the hidden layer  2020 , one or more nodes of the input layer  2010  may not be connected to one or more nodes of the hidden layer  2020 . 
     In particular embodiments, an ANN may be a feedforward ANN (e.g., an ANN with no cycles or loops where communication between nodes flows in one direction beginning with the input layer and proceeding to successive layers). As an example and not by way of limitation, the input to each node of the hidden layer  2020  may comprise the output of one or more nodes of the input layer  2010 . As another example and not by way of limitation, the input to each node of the output layer  2050  may comprise the output of one or more nodes of the hidden layer  2040 . In particular embodiments, an ANN may be a deep neural network (e.g., a neural network comprising at least two hidden layers). In particular embodiments, an ANN may be a deep residual network. A deep residual network may be a feedforward ANN comprising hidden layers organized into residual blocks. The input into each residual block after the first residual block may be a function of the output of the previous residual block and the input of the previous residual block. As an example and not by way of limitation, the input into residual block N may be F(x)+x, where F(x) may be the output of residual block N−1, x may be the input into residual block N−1. Although this disclosure describes a particular ANN, this disclosure contemplates any suitable ANN. 
     In particular embodiments, an activation function may correspond to each node of an ANN. An activation function of a node may define the output of a node for a given input. In particular embodiments, an input to a node may comprise a set of inputs. As an example and not by way of limitation, an activation function may be an identity function, a binary step function, a logistic function, or any other suitable function. As another example and not by way of limitation, an activation function for a node k may be the sigmoid function 
     
       
         
           
             
               
                 
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     the rectifier F k (s k )=max(0, s k ), or any other suitable function F k  (s k ), where s k  may be the effective input to node k. In particular embodiments, the input of an activation function corresponding to a node may be weighted. Each node may generate output using a corresponding activation function based on weighted inputs. In particular embodiments, each connection between nodes may be associated with a weight. As an example and not by way of limitation, a connection  2025  between the node  2005  and the node  2015  may have a weighting coefficient of 0.4, which may indicate that 0.4 multiplied by the output of the node  2005  is used as an input to the node  2015 . As another example and not by way of limitation, the output y k  of node k may be y k =F k  (s k ), where F k  may be the activation function corresponding to node k, s k =Σ j (w jk x j ) may be the effective input to node k, x j  may be the output of a node j connected to node k, and w ik  may be the weighting coefficient between node j and node k. In particular embodiments, the input to nodes of the input layer may be based on a vector representing an object. Although this disclosure describes particular inputs to and outputs of nodes, this disclosure contemplates any suitable inputs to and outputs of nodes. Moreover, although this disclosure may describe particular connections and weights between nodes, this disclosure contemplates any suitable connections and weights between nodes. 
     In particular embodiments, an ANN may be trained using training data. As an example and not by way of limitation, training data may comprise inputs to the ANN  2000  and an expected output. As another example and not by way of limitation, training data may comprise vectors each representing a training object and an expected label for each training object. In particular embodiments, training an ANN may comprise modifying the weights associated with the connections between nodes of the ANN by optimizing an objective function. As an example and not by way of limitation, a training method may be used (e.g., the conjugate gradient method, the gradient descent method, the stochastic gradient descent) to backpropagate the sum-of-squares error measured as a distances between each vector representing a training object (e.g., using a cost function that minimizes the sum-of-squares error). In particular embodiments, an ANN may be trained using a dropout technique. As an example and not by way of limitation, one or more nodes may be temporarily omitted (e.g., receive no input and generate no output) while training. For each training object, one or more nodes of the ANN may have some probability of being omitted. The nodes that are omitted for a particular training object may be different than the nodes omitted for other training objects (e.g., the nodes may be temporarily omitted on an object-by-object basis). Although this disclosure describes training an ANN in a particular manner, this disclosure contemplates training an ANN in any suitable manner. 
     Privacy 
     In particular embodiments, one or more objects (e.g., content or other types of objects) of a computing system may be associated with one or more privacy settings. The one or more objects may be stored on or otherwise associated with any suitable computing system or application, such as, for example, a social-networking system  160 , a client system  130 , an assistant system  140 , a third-party system  170 , a social-networking application, an assistant application, a messaging application, a photo-sharing application, or any other suitable computing system or application. Although the examples discussed herein are in the context of an online social network, these privacy settings may be applied to any other suitable computing system. Privacy settings (or “access settings”) for an object may be stored in any suitable manner, such as, for example, in association with the object, in an index on an authorization server, in another suitable manner, or any suitable combination thereof. A privacy setting for an object may specify how the object (or particular information associated with the object) can be accessed, stored, or otherwise used (e.g., viewed, shared, modified, copied, executed, surfaced, or identified) within the online social network. When privacy settings for an object allow a particular user or other entity to access that object, the object may be described as being “visible” with respect to that user or other entity. As an example and not by way of limitation, a user of the online social network may specify privacy settings for a user-profile page that identify a set of users that may access work-experience information on the user-profile page, thus excluding other users from accessing that information. 
     In particular embodiments, privacy settings for an object may specify a “blocked list” of users or other entities that should not be allowed to access certain information associated with the object. In particular embodiments, the blocked list may include third-party entities. The blocked list may specify one or more users or entities for which an object is not visible. As an example and not by way of limitation, a user may specify a set of users who may not access photo albums associated with the user, thus excluding those users from accessing the photo albums (while also possibly allowing certain users not within the specified set of users to access the photo albums). In particular embodiments, privacy settings may be associated with particular social-graph elements. Privacy settings of a social-graph element, such as a node or an edge, may specify how the social-graph element, information associated with the social-graph element, or objects associated with the social-graph element can be accessed using the online social network. As an example and not by way of limitation, a particular concept node  1804  corresponding to a particular photo may have a privacy setting specifying that the photo may be accessed only by users tagged in the photo and friends of the users tagged in the photo. In particular embodiments, privacy settings may allow users to opt in to or opt out of having their content, information, or actions stored/logged by the social-networking system  160  or assistant system  140  or shared with other systems (e.g., a third-party system  170 ). Although this disclosure describes using particular privacy settings in a particular manner, this disclosure contemplates using any suitable privacy settings in any suitable manner. 
     In particular embodiments, privacy settings may be based on one or more nodes or edges of a social graph  1800 . A privacy setting may be specified for one or more edges  1806  or edge-types of the social graph  1800 , or with respect to one or more nodes  1802 ,  1804  or node-types of the social graph  1800 . The privacy settings applied to a particular edge  1806  connecting two nodes may control whether the relationship between the two entities corresponding to the nodes is visible to other users of the online social network. Similarly, the privacy settings applied to a particular node may control whether the user or concept corresponding to the node is visible to other users of the online social network. As an example and not by way of limitation, a first user may share an object to the social-networking system  160 . The object may be associated with a concept node  1804  connected to a user node  1802  of the first user by an edge  1806 . The first user may specify privacy settings that apply to a particular edge  1806  connecting to the concept node  1804  of the object, or may specify privacy settings that apply to all edges  1806  connecting to the concept node  1804 . As another example and not by way of limitation, the first user may share a set of objects of a particular object-type (e.g., a set of images). The first user may specify privacy settings with respect to all objects associated with the first user of that particular object-type as having a particular privacy setting (e.g., specifying that all images posted by the first user are visible only to friends of the first user and/or users tagged in the images). 
     In particular embodiments, the social-networking system  160  may present a “privacy wizard” (e.g., within a webpage, a module, one or more dialog boxes, or any other suitable interface) to the first user to assist the first user in specifying one or more privacy settings. The privacy wizard may display instructions, suitable privacy-related information, current privacy settings, one or more input fields for accepting one or more inputs from the first user specifying a change or confirmation of privacy settings, or any suitable combination thereof. In particular embodiments, the social-networking system  160  may offer a “dashboard” functionality to the first user that may display, to the first user, current privacy settings of the first user. The dashboard functionality may be displayed to the first user at any appropriate time (e.g., following an input from the first user summoning the dashboard functionality, following the occurrence of a particular event or trigger action). The dashboard functionality may allow the first user to modify one or more of the first user&#39;s current privacy settings at any time, in any suitable manner (e.g., redirecting the first user to the privacy wizard). 
     Privacy settings associated with an object may specify any suitable granularity of permitted access or denial of access. As an example and not by way of limitation, access or denial of access may be specified for particular users (e.g., only me, my roommates, my boss), users within a particular degree-of-separation (e.g., friends, friends-of-friends), user groups (e.g., the gaming club, my family), user networks (e.g., employees of particular employers, students or alumni of particular university), all users (“public”), no users (“private”), users of third-party systems  170 , particular applications (e.g., third-party applications, external websites), other suitable entities, or any suitable combination thereof. Although this disclosure describes particular granularities of permitted access or denial of access, this disclosure contemplates any suitable granularities of permitted access or denial of access. 
     In particular embodiments, one or more servers  162  may be authorization/privacy servers for enforcing privacy settings. In response to a request from a user (or other entity) for a particular object stored in a data store  164 , the social-networking system  160  may send a request to the data store  164  for the object. The request may identify the user associated with the request and the object may be sent only to the user (or a client system  130  of the user) if the authorization server determines that the user is authorized to access the object based on the privacy settings associated with the object. If the requesting user is not authorized to access the object, the authorization server may prevent the requested object from being retrieved from the data store  164  or may prevent the requested object from being sent to the user. In the search-query context, an object may be provided as a search result only if the querying user is authorized to access the object, e.g., if the privacy settings for the object allow it to be surfaced to, discovered by, or otherwise visible to the querying user. In particular embodiments, an object may represent content that is visible to a user through a newsfeed of the user. As an example and not by way of limitation, one or more objects may be visible to a user&#39;s “Trending” page. In particular embodiments, an object may correspond to a particular user. The object may be content associated with the particular user, or may be the particular user&#39;s account or information stored on the social-networking system  160 , or other computing system. As an example and not by way of limitation, a first user may view one or more second users of an online social network through a “People You May Know” function of the online social network, or by viewing a list of friends of the first user. As an example and not by way of limitation, a first user may specify that they do not wish to see objects associated with a particular second user in their newsfeed or friends list. If the privacy settings for the object do not allow it to be surfaced to, discovered by, or visible to the user, the object may be excluded from the search results. Although this disclosure describes enforcing privacy settings in a particular manner, this disclosure contemplates enforcing privacy settings in any suitable manner. 
     In particular embodiments, different objects of the same type associated with a user may have different privacy settings. Different types of objects associated with a user may have different types of privacy settings. As an example and not by way of limitation, a first user may specify that the first user&#39;s status updates are public, but any images shared by the first user are visible only to the first user&#39;s friends on the online social network. As another example and not by way of limitation, a user may specify different privacy settings for different types of entities, such as individual users, friends-of-friends, followers, user groups, or corporate entities. As another example and not by way of limitation, a first user may specify a group of users that may view videos posted by the first user, while keeping the videos from being visible to the first user&#39;s employer. In particular embodiments, different privacy settings may be provided for different user groups or user demographics. As an example and not by way of limitation, a first user may specify that other users who attend the same university as the first user may view the first user&#39;s pictures, but that other users who are family members of the first user may not view those same pictures. 
     In particular embodiments, the social-networking system  160  may provide one or more default privacy settings for each object of a particular object-type. A privacy setting for an object that is set to a default may be changed by a user associated with that object. As an example and not by way of limitation, all images posted by a first user may have a default privacy setting of being visible only to friends of the first user and, for a particular image, the first user may change the privacy setting for the image to be visible to friends and friends-of-friends. 
     In particular embodiments, privacy settings may allow a first user to specify (e.g., by opting out, by not opting in) whether the social-networking system  160  or assistant system  140  may receive, collect, log, or store particular objects or information associated with the user for any purpose. In particular embodiments, privacy settings may allow the first user to specify whether particular applications or processes may access, store, or use particular objects or information associated with the user. The privacy settings may allow the first user to opt in or opt out of having objects or information accessed, stored, or used by specific applications or processes. The social-networking system  160  or assistant system  140  may access such information in order to provide a particular function or service to the first user, without the social-networking system  160  or assistant system  140  having access to that information for any other purposes. Before accessing, storing, or using such objects or information, the social-networking system  160  or assistant system  140  may prompt the user to provide privacy settings specifying which applications or processes, if any, may access, store, or use the object or information prior to allowing any such action. As an example and not by way of limitation, a first user may transmit a message to a second user via an application related to the online social network (e.g., a messaging app), and may specify privacy settings that such messages should not be stored by the social-networking system  160  or assistant system  140 . 
     In particular embodiments, a user may specify whether particular types of objects or information associated with the first user may be accessed, stored, or used by the social-networking system  160  or assistant system  140 . As an example and not by way of limitation, the first user may specify that images sent by the first user through the social-networking system  160  or assistant system  140  may not be stored by the social-networking system  160  or assistant system  140 . As another example and not by way of limitation, a first user may specify that messages sent from the first user to a particular second user may not be stored by the social-networking system  160  or assistant system  140 . As yet another example and not by way of limitation, a first user may specify that all objects sent via a particular application may be saved by the social-networking system  160  or assistant system  140 . 
     In particular embodiments, privacy settings may allow a first user to specify whether particular objects or information associated with the first user may be accessed from particular client systems  130  or third-party systems  170 . The privacy settings may allow the first user to opt in or opt out of having objects or information accessed from a particular device (e.g., the phone book on a user&#39;s smart phone), from a particular application (e.g., a messaging app), or from a particular system (e.g., an email server). The social-networking system  160  or assistant system  140  may provide default privacy settings with respect to each device, system, or application, and/or the first user may be prompted to specify a particular privacy setting for each context. As an example and not by way of limitation, the first user may utilize a location-services feature of the social-networking system  160  or assistant system  140  to provide recommendations for restaurants or other places in proximity to the user. The first user&#39;s default privacy settings may specify that the social-networking system  160  or assistant system  140  may use location information provided from a client system  130  of the first user to provide the location-based services, but that the social-networking system  160  or assistant system  140  may not store the location information of the first user or provide it to any third-party system  170 . The first user may then update the privacy settings to allow location information to be used by a third-party image-sharing application in order to geo-tag photos. 
     In particular embodiments, privacy settings may allow a user to specify one or more geographic locations from which objects can be accessed. Access or denial of access to the objects may depend on the geographic location of a user who is attempting to access the objects. As an example and not by way of limitation, a user may share an object and specify that only users in the same city may access or view the object. As another example and not by way of limitation, a first user may share an object and specify that the object is visible to second users only while the first user is in a particular location. If the first user leaves the particular location, the object may no longer be visible to the second users. As another example and not by way of limitation, a first user may specify that an object is visible only to second users within a threshold distance from the first user. If the first user subsequently changes location, the original second users with access to the object may lose access, while a new group of second users may gain access as they come within the threshold distance of the first user. 
     In particular embodiments, the social-networking system  160  or assistant system  140  may have functionalities that may use, as inputs, personal or biometric information of a user for user-authentication or experience-personalization purposes. A user may opt to make use of these functionalities to enhance their experience on the online social network. As an example and not by way of limitation, a user may provide personal or biometric information to the social-networking system  160  or assistant system  140 . The user&#39;s privacy settings may specify that such information may be used only for particular processes, such as authentication, and further specify that such information may not be shared with any third-party system  170  or used for other processes or applications associated with the social-networking system  160  or assistant system  140 . As another example and not by way of limitation, the social-networking system  160  may provide a functionality for a user to provide voice-print recordings to the online social network. As an example and not by way of limitation, if a user wishes to utilize this function of the online social network, the user may provide a voice recording of his or her own voice to provide a status update on the online social network. The recording of the voice-input may be compared to a voice print of the user to determine what words were spoken by the user. The user&#39;s privacy setting may specify that such voice recording may be used only for voice-input purposes (e.g., to authenticate the user, to send voice messages, to improve voice recognition in order to use voice-operated features of the online social network), and further specify that such voice recording may not be shared with any third-party system  170  or used by other processes or applications associated with the social-networking system  160 . As another example and not by way of limitation, the social-networking system  160  may provide a functionality for a user to provide a reference image (e.g., a facial profile, a retinal scan) to the online social network. The online social network may compare the reference image against a later-received image input (e.g., to authenticate the user, to tag the user in photos). The user&#39;s privacy setting may specify that such image may be used only for a limited purpose (e.g., authentication, tagging the user in photos), and further specify that such image may not be shared with any third-party system  170  or used by other processes or applications associated with the social-networking system  160 . 
     Systems and Methods 
       FIG.  21    illustrates an example computer system  2100 . In particular embodiments, one or more computer systems  2100  perform one or more steps of one or more methods described or illustrated herein. In particular embodiments, one or more computer systems  2100  provide functionality described or illustrated herein. In particular embodiments, software running on one or more computer systems  2100  performs one or more steps of one or more methods described or illustrated herein or provides functionality described or illustrated herein. Particular embodiments include one or more portions of one or more computer systems  2100 . Herein, reference to a computer system may encompass a computing device, and vice versa, where appropriate. Moreover, reference to a computer system may encompass one or more computer systems, where appropriate. 
     This disclosure contemplates any suitable number of computer systems  2100 . This disclosure contemplates computer system  2100  taking any suitable physical form. As example and not by way of limitation, computer system  2100  may be an embedded computer system, a system-on-chip (SOC), a single-board computer system (SBC) (such as, for example, a computer-on-module (COM) or system-on-module (SOM)), a desktop computer system, a laptop or notebook computer system, an interactive kiosk, a mainframe, a mesh of computer systems, a mobile telephone, a personal digital assistant (PDA), a server, a tablet computer system, or a combination of two or more of these. Where appropriate, computer system  2100  may include one or more computer systems  2100 ; be unitary or distributed; span multiple locations; span multiple machines; span multiple data centers; or reside in a cloud, which may include one or more cloud components in one or more networks. Where appropriate, one or more computer systems  2100  may perform without substantial spatial or temporal limitation one or more steps of one or more methods described or illustrated herein. As an example and not by way of limitation, one or more computer systems  2100  may perform in real time or in batch mode one or more steps of one or more methods described or illustrated herein. One or more computer systems  2100  may perform at different times or at different locations one or more steps of one or more methods described or illustrated herein, where appropriate. 
     In particular embodiments, computer system  2100  includes a processor  2102 , memory  2104 , storage  2106 , an input/output (I/O) interface  2108 , a communication interface  2110 , and a bus  2112 . Although this disclosure describes and illustrates a particular computer system having a particular number of particular components in a particular arrangement, this disclosure contemplates any suitable computer system having any suitable number of any suitable components in any suitable arrangement. 
     In particular embodiments, processor  2102  includes hardware for executing instructions, such as those making up a computer program. As an example and not by way of limitation, to execute instructions, processor  2102  may retrieve (or fetch) the instructions from an internal register, an internal cache, memory  2104 , or storage  2106 ; decode and execute them; and then write one or more results to an internal register, an internal cache, memory  2104 , or storage  2106 . In particular embodiments, processor  2102  may include one or more internal caches for data, instructions, or addresses. This disclosure contemplates processor  2102  including any suitable number of any suitable internal caches, where appropriate. As an example and not by way of limitation, processor  2102  may include one or more instruction caches, one or more data caches, and one or more translation lookaside buffers (TLBs). Instructions in the instruction caches may be copies of instructions in memory  2104  or storage  2106 , and the instruction caches may speed up retrieval of those instructions by processor  2102 . Data in the data caches may be copies of data in memory  2104  or storage  2106  for instructions executing at processor  2102  to operate on; the results of previous instructions executed at processor  2102  for access by subsequent instructions executing at processor  2102  or for writing to memory  2104  or storage  2106 ; or other suitable data. The data caches may speed up read or write operations by processor  2102 . The TLBs may speed up virtual-address translation for processor  2102 . In particular embodiments, processor  2102  may include one or more internal registers for data, instructions, or addresses. This disclosure contemplates processor  2102  including any suitable number of any suitable internal registers, where appropriate. Where appropriate, processor  2102  may include one or more arithmetic logic units (ALUs); be a multi-core processor; or include one or more processors  2102 . Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor. 
     In particular embodiments, memory  2104  includes main memory for storing instructions for processor  2102  to execute or data for processor  2102  to operate on. As an example and not by way of limitation, computer system  2100  may load instructions from storage  2106  or another source (such as, for example, another computer system  2100 ) to memory  2104 . Processor  2102  may then load the instructions from memory  2104  to an internal register or internal cache. To execute the instructions, processor  2102  may retrieve the instructions from the internal register or internal cache and decode them. During or after execution of the instructions, processor  2102  may write one or more results (which may be intermediate or final results) to the internal register or internal cache. Processor  2102  may then write one or more of those results to memory  2104 . In particular embodiments, processor  2102  executes only instructions in one or more internal registers or internal caches or in memory  2104  (as opposed to storage  2106  or elsewhere) and operates only on data in one or more internal registers or internal caches or in memory  2104  (as opposed to storage  2106  or elsewhere). One or more memory buses (which may each include an address bus and a data bus) may couple processor  2102  to memory  2104 . Bus  2112  may include one or more memory buses, as described below. In particular embodiments, one or more memory management units (MMUs) reside between processor  2102  and memory  2104  and facilitate accesses to memory  2104  requested by processor  2102 . In particular embodiments, memory  2104  includes random access memory (RAM). This RAM may be volatile memory, where appropriate. Where appropriate, this RAM may be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where appropriate, this RAM may be single-ported or multi-ported RAM. This disclosure contemplates any suitable RAM. Memory  2104  may include one or more memories  2104 , where appropriate. Although this disclosure describes and illustrates particular memory, this disclosure contemplates any suitable memory. 
     In particular embodiments, storage  2106  includes mass storage for data or instructions. As an example and not by way of limitation, storage  2106  may include a hard disk drive (HDD), a floppy disk drive, flash memory, an optical disc, a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB) drive or a combination of two or more of these. Storage  2106  may include removable or non-removable (or fixed) media, where appropriate. Storage  2106  may be internal or external to computer system  2100 , where appropriate. In particular embodiments, storage  2106  is non-volatile, solid-state memory. In particular embodiments, storage  2106  includes read-only memory (ROM). Where appropriate, this ROM may be mask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM), or flash memory or a combination of two or more of these. This disclosure contemplates mass storage  2106  taking any suitable physical form. Storage  2106  may include one or more storage control units facilitating communication between processor  2102  and storage  2106 , where appropriate. Where appropriate, storage  2106  may include one or more storages  2106 . Although this disclosure describes and illustrates particular storage, this disclosure contemplates any suitable storage. 
     In particular embodiments, I/O interface  2108  includes hardware, software, or both, providing one or more interfaces for communication between computer system  2100  and one or more I/O devices. Computer system  2100  may include one or more of these I/O devices, where appropriate. One or more of these I/O devices may enable communication between a person and computer system  2100 . As an example and not by way of limitation, an I/O device may include a keyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker, still camera, stylus, tablet, touch screen, trackball, video camera, another suitable I/O device or a combination of two or more of these. An I/O device may include one or more sensors. This disclosure contemplates any suitable I/O devices and any suitable I/O interfaces  2108  for them. Where appropriate, I/O interface  2108  may include one or more device or software drivers enabling processor  2102  to drive one or more of these I/O devices. I/O interface  2108  may include one or more I/O interfaces  2108 , where appropriate. Although this disclosure describes and illustrates a particular I/O interface, this disclosure contemplates any suitable I/O interface. 
     In particular embodiments, communication interface  2110  includes hardware, software, or both providing one or more interfaces for communication (such as, for example, packet-based communication) between computer system  2100  and one or more other computer systems  2100  or one or more networks. As an example and not by way of limitation, communication interface  2110  may include a network interface controller (NIC) or network adapter for communicating with an Ethernet or other wire-based network or a wireless NIC (WNIC) or wireless adapter for communicating with a wireless network, such as a WI-FI network. This disclosure contemplates any suitable network and any suitable communication interface  2110  for it. As an example and not by way of limitation, computer system  2100  may communicate with an ad hoc network, a personal area network (PAN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), or one or more portions of the Internet or a combination of two or more of these. One or more portions of one or more of these networks may be wired or wireless. As an example, computer system  2100  may communicate with a wireless PAN (WPAN) (such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAX network, a cellular telephone network (such as, for example, a Global System for Mobile Communications (GSM) network), or other suitable wireless network or a combination of two or more of these. Computer system  2100  may include any suitable communication interface  2110  for any of these networks, where appropriate. Communication interface  2110  may include one or more communication interfaces  2110 , where appropriate. Although this disclosure describes and illustrates a particular communication interface, this disclosure contemplates any suitable communication interface. 
     In particular embodiments, bus  2112  includes hardware, software, or both coupling components of computer system  2100  to each other. As an example and not by way of limitation, bus  2112  may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or another suitable bus or a combination of two or more of these. Bus  2112  may include one or more buses  2112 , where appropriate. Although this disclosure describes and illustrates a particular bus, this disclosure contemplates any suitable bus or interconnect. 
     Herein, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (ICs) (such, as for example, field-programmable gate arrays (FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or drives, any other suitable computer-readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate. 
     Miscellaneous 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, feature, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although this disclosure describes or illustrates particular embodiments as providing particular advantages, particular embodiments may provide none, some, or all of these advantages.