Abstract:
Methods and apparatus are provided for collecting proxy presence information about an object associated with a user from one or more proxy presence sources associated with the user. A proxy presence agent is associated with each of the proxy presence sources; and the proxy presence agents provide proxy presence information to one or more presence servers. The object may be, for example, one or more of a business document, an application document, or one or more runtime objects associated with the user. The proxy presence agent reports one or more of macropresence events and micropresence events related to the object. A continuous presence function is generated for each of the proxy presence sources that characterizes the likelihood that the object is active at the corresponding presence source at a given time. The proxy presence sources may include, for example, one or more business applications, application execution environments, devices or locations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. patent application Ser. No. 10/999,901, entitled “Methods and Apparatus for Determining a Presence of a User,” filed contemporaneously herewith and incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates generally to communication methods and systems, and more particularly, to methods and systems that determine the presence of a user based on multiple sources of presence information. 
     BACKGROUND OF THE INVENTION 
     A number of techniques have been proposed or suggested for determining whether or not a person is “present” at a given device, location or application. Presence information is becoming increasingly important for many applications. For example, as friends and colleagues become more distributed in time or location (or both), it becomes even more desirable for a user to determine, prior to a given communication attempt, whether or not the intended recipient of the contemplated communication is currently available at one or more communication devices. The provided presence information allows a user to make a more informed decision about how to best communicate with another person. In this manner, productivity is enhanced by enabling a better selection of the best way to contact the other person. This informed choice leads to a more efficient, productive and cost effective communication. 
     Determining a user&#39;s presence and availability at a given device, location or application can generally not be done with certainty. Presence and availability are a prediction of current presence and availability based on presence and availability in the past (i.e., either the immediate past or over an extended history). For example, presence information based on login activity (e.g., whether the user is currently logged on to a given service) can grow stale over time, since a user may remain logged in to an application for several days at a time. Thus, many presence-tracking systems supplement the user login activity with other determinable user activity, such as keyboard or mouse activity and whether a user remains idle for a time period exceeding a specified interval. Existing presence awareness systems can distinguish between a user who is connected to the service (present) or not connected to the service (absent), and most systems allow some sort of busy or unavailable flag to be set. 
     A number of techniques have been proposed or suggested for evaluating the likelihood that a user will be present at a device or location at some time, t, based on knowledge that the user was present at the device or location at some prior time. Such techniques are sometimes referred to as “presence aging.” For example, Horvitz et al., “Coordinate: Probabilistic Forecasting of Presence and Availability,” 18 th  Conf. on Uncertainty and Artificial Intelligence, 224-233 (July, 2002), describes a system that attempts to predict a user&#39;s presence and availability based on historical data, as well as future known data about the user&#39;s activities, for example, from a user&#39;s calendar. The Horvitz system attempts to evaluate the probability of the user&#39;s presence and availability being associated with one or more discrete presence/availability states. 
     While existing presence awareness systems provide valuable presence information, they suffer from a number of limitations, which if overcome, could further improve the ability of users to efficiently communicate. For example, existing presence awareness systems are typically proprietary, closed architecture systems that only provide presence information within the domain of the service provider (i.e., one service subscriber can only determine if another service subscriber is present). Moreover, such systems typically require the user to actively perform a system login before these systems can track user presence and availability. In addition, existing presence aging techniques employ discrete stepwise functions that consider a presence state, such as “available,” to be in full effect until a certain time interval (or event) has passed, then the presence state changes to another, generally lower, discrete value, such as “away.” 
     A need therefore exists for methods and systems that can evaluate a number of different sources of presence information for a user, independent of the providers of the devices and systems that constitute presence sources and without requiring active user logins, using a presence agent associated with each source of presence information. A further need exists for a method and apparatus for evaluating presence information on a continuous scale. 
     SUMMARY OF THE INVENTION 
     Generally, methods and apparatus are provided for collecting proxy presence information about an object associated with a user from one or more proxy presence sources associated with the user. A proxy presence agent is associated with each of the proxy presence sources; and the proxy presence agents provide proxy presence information to one or more presence servers. The object may be, for example, one or more of a business document, an application document, or one or more runtime objects associated with the user. The proxy presence agent reports one or more of macropresence events and micropresence events related to the object. 
     According to another aspect of the invention, a continuous presence function is generated for each of the proxy presence sources that characterizes the likelihood that the object is active at the corresponding presence source at a given time. The continuous presence functions are optionally recomputed if a time since a last computation exceeds a threshold. The proxy presence sources may include, for example, one or more business applications, application execution environments, devices or locations. 
     A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a network environment where the present invention can operate; 
         FIGS. 2 and 3  illustrate two exemplary presence functions for different presence sources, s, as a function of a time difference between the current time and earlier presence events; 
         FIG. 4  is a flow chart describing an exemplary implementation of the software agent process of  FIG. 1 ; 
         FIG. 5  is a schematic block diagram of an exemplary presence server of  FIG. 1 ; 
         FIG. 6  is a flow chart describing an exemplary implementation of a presence information maintenance process of  FIG. 5 ; 
         FIG. 7  is a flow chart describing an exemplary implementation of a presence information request process of  FIG. 5 ; and 
         FIG. 8  is a sample table for an exemplary database trigger database that records one or more database triggers that can be used to report presence events to a proxy presence agent of a user. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides techniques for approximating the current presence and availability status of a user.  FIG. 1  illustrates a network environment  100  where the present invention can operate. As shown in  FIG. 1 , a number of users communicate over one or more wired or wireless networks  150 . In the exemplary embodiment, each user employs a mobile telephone  110 . While the present invention is illustrated in the context of mobile telephones  110 , the invention may be applied to many other devices and applications, as would be apparent to a person of ordinary skill in the art. 
     Macropresence 
     According to one aspect of the invention, a software agent  400 , discussed below in conjunction with  FIG. 4 , is deployed on a mobile phone device  110 . The software agent  400  automatically reports powering up and down the phone device to a presence server  500 , discussed below in conjunction with  FIGS. 5 through 7 . The interval between the device “on” and “off” events constitutes the phone user&#39;s macropresence. Subscribers to this user&#39;s macropresence through the presence server  500  can thus be notified when the user turns on or off the phone  110  or of other presence events. In one exemplary implementation, the user of the phone device  110  does not have to invoke any software on the phone  110  nor does the user have to use any software to explicitly propagate macropresence changes to the presence server  500 . In other words, there is no effort or intervention required from the user to indicate macropresence changes. Moreover, because this process of reporting macropresence changes to a presence server  500  is automatic, the user cannot forget to indicate or to report a macropresence change. 
     A presence subscriber, such as applications and other users, may be interested in a user&#39;s macropresence as one of potentially many disparate sources of presence information about this user. A subscriber to a user&#39;s macropresence might use macropresence to influence the routing of communications to this user. For example, if the macropresence subscriber knows that the user has turned on his or her mobile phone  110 , the macropresence subscriber could decide to route a phone call to the user&#39;s mobile phone  110  rather than to his or her desk phone or to send an email or instant message to the email/instant message address associated with her mobile phone  110  rather than that associated with their work environment. 
     In the illustrative embodiment, the software agent  400  is deployed on the mobile phone  110  rather than in the phone provider&#39;s network  150 . Thus, in such an embodiment, reporting mobile phone macropresence is independent of the provider network  150  and its capabilities. However, there may be situations where it is desirable to have the provider network  150  host the macropresence reporting software, e.g., in cases where mobile phones are not capable of running additional software or where a network provider would like to offer a fee-based macropresence service. In such cases, the phone network provider can offer the same functionality of reporting macropresence by using software in the phone network  150 . 
     Micropresence 
     The present invention recognizes that mobile phone users tend to leave their mobile phones on for extended periods of time even though they may not be truly available on their mobile phones. For example, mobile phone users might leave their phone in their car while being in a store. A mobile phone user might mute the ringer of the phone while being in a movie theater. In such cases, the user&#39;s macropresence cannot be used to accurately infer the availability of the user to receive communications at that time. 
     Thus, according to another aspect of the invention, micropresence supplements macropresence information with button press events and channel usage information on the mobile phone  110 . In between mobile phone “on” and “off” events, there is typically a sequence of button pushes related to user activities such as receiving calls, making calls, checking voice mail, running applications, receiving messages, changing ring tones and modifying the configurations of the phone. The software agent  400  can propagate macropresence changes to the presence server  500 , as well as button presses and other user activities. 
     The accuracy of decisions based on presence information is directly related to how recently a reported macropresence or micropresence event occurred. However, a presence server  500  can be easily overwhelmed with micropresence events if a large number of mobile phones  110  report micropresence events. To prevent flooding of the presence server, the number of micropresence events may be limited by only propagating micropresence events to the presence server  500  from a given mobile phone  110  if no such event has been propagated to the server  500  in the last t ƒ  time units, where t ƒ —is a configurable parameter in the software agent  400 . To this end, the software agent  400  keeps track of the time of the last micropresence event that was propagated to the presence server. If the next event falls within t f  time units of the last recorded event, the event will not be propagated to the presence server. 
     The macropresence and micropresence information collected by the presence agent  400  is independent of the service provider associated with the mobile telephone  110  and independent of the technology employed by the service provider. The presence agent  400 , deployed on the mobile telephone  110  itself, can thus provide presence information to any application outside of the realm of the service provider. 
     In addition, because the presence agent  400  is deployed on the mobile telephone  110  itself, the presence agent  400  has access to all button presses on the telephone  110 , whether or not such button presses result in a transmission to the service provider (who only knows of transmitted events). For example, if a user locks or unlocks the telephone  110  or checks a call log, these operations do not result in communications and would not be known to the service provider but would be known to the presence agent  400  (and can be propagated to the presence server). 
     Presence Aging and Fuzzy Presence 
     When a subscriber to a user&#39;s macropresence and micropresence needs to make a decision based on the user&#39;s presence on a device or application or at a location, the last reported macro presence or micropresence event for this user lies in the past. Depending on how long ago the last event of this kind was, it may not be a good indication of what the user&#39;s current presence and availability is. This effect is referred to as presence aging. 
     Another aspect of the invention ranks presence events, originating at all presence event sources including mobile phone macropresence and micropresence, according to the timeliness of presence events. To each element s in the set S(u) of presence event sources for a user, u, a monotonically decreasing and continuous function f u,s (d) is applied as a function of the time difference d between the current time and the last presence event originating at s. The most appropriate function f u,s  can be determined based on experimental results. To determine the likeliest device or application or location that a user is present and available at, the function f u,s  is computed for each presence source s and the list of computed values is sorted in descending order. The presence source at the top of the list is generally associated with the presence source that the user is likeliest to be present and available at. Evaluation of the function f u,s  indicates the user&#39;s current level of presence/availability, on a continuous scale, based on the type of presence source and the amount of time that has passed since the last presence event from that presence source (as opposed to a history of past presence events). 
     As discussed further below, the continuous values of presence/availability levels provided by the present invention allow the presence/availability levels of a user to be aggregated across all presence sources for this user and subsets of a given set of users to be identified with certain presence/availability levels (such as the most available user, the least available user, and the subset of users with a certain minimum or maximum presence/availability level). 
     The values of f u,s (d) are referred to as fuzzy presence values to distinguish them from the known concept of discrete presence states. The latter are equivalent to using discrete functions with non-numerical values instead of continuous functions. A discrete presence state could be “available” or “away” or “extended away,” to use an example from the instant messaging world. The uncertainty about a user&#39;s presence status at a presence source is better accounted for by fuzzy presence, i.e., by continuous functions rather than by discrete functions. More importantly, using continuous functions instead of discrete functions with non-numerical values allows computations on presence values to be performed much more easily and efficiently. For example, computing the average or a weighted average for f u,s  at all presence sources s at a given point d for a specific user u is trivial and would allow the presence subscriber to easily discern the “overall presence” of this user. Comparing the overall presence values for different users is a potentially very useful exercise. 
     If a presence subscriber is not interested in determining a specific user&#39;s presence but rather in the question of who is the “most” available person f(U) among a set U of users, the presence subscriber could easily compute the following value:
 
 f ( U )=max { f   u,s ( d )| u εU,s εS ( u )}.
 
This concept of the “most” available person may be applied, for example, in a help desk where a dispatcher (a presence subscriber) needs to find the first available help desk person. It is again noted that the use of continuous functions f u,s  makes the computation of the function f(U) very simple and efficient.
 
     This concept of the “most” available person may be extrapolated to compute subsets of U with a given minimum or maximum level of presence/availability or subsets that fall into a given interval of presence/availability levels. For example, the subset of U that includes all the users whose presence/availability does not exceed 0.1 and who therefore have to be reminded of the necessity to be more available to customer questions can be identified, for example, for a manager or supervisor. Alternatively, the subsets of all users whose presence/availability level exceeds 0.85 can be identified on behalf of an important customer that needs to speak to an expert in U as quickly as possible. 
     In order to deal with presence aging, a user could be prompted to interact with the presence source s to confirm and refresh his or her presence and availability status, if the value of the function f u,s  falls below a configurable threshold t s . In the case of a mobile phone  110  as the source of macropresence and micropresence events, the software agent  400  that reports macropresence and micropresence events can optionally prompt the user through a visual or acoustic signal to press an arbitrary button if the value of f u,s  falls below the threshold t s . The button would count as a micropresence event as described above. The use of fuzzy presence allows fine-grained values to be selected for t s , compared with discrete presence states. 
     In one exemplary implementation, a user can change, override, or influence the value of f u,s  for a given presence source s and at a given point d. Changing the value of f u,s  either manually or through a presence application or an application that influences presence values, allows the user to determine or establish how available he or she wants to be to a presence subscriber. A more fine-grained approach would be to adjust the value of f u,s  differently for different presence subscribers. For example, users could choose to be 0.9 available for their superior but only 0.3 available for presence subscribers outside their department. 
       FIGS. 2 and 3  are graphs illustrating two exemplary presence functions for different presence sources, s, as a function of the time difference d between the current time and earlier presence events originating at s. For example, consider a user A having two presence sources, a mobile phone and an IM client, i.e., S equals {cellphone, IMclient}. Two presence functions are defined, f A,cellPhone  and f A,IMclient , and assume the experience with user A in these two functions reflects that presence levels for user A on the mobile phone decrease more rapidly than presence levels on the IM client. Thus, the exemplary functions are defined as followed:
 
 f   A,cellPhone ( d )=25/( d+ 25); and
 
 f   A,IMclient ( d )=10/( √{square root over (d)} +10).
 
     Suppose A is a member of the universe U of all database experts in an organization and the subscriber to A&#39;s presence is an expert locator application that is looking for a database expert at 10:05 AM on a given day. It is assumed that the last time A touched a button on her mobile phone was at time t cellPhone  equal to 9:20 AM on the same day and the last time she used her IM client was at time t IMclient  equal to 8:35 AM on the same day. Assume further that the presence subscriber in question prefers an expert available on voice over an expert available on IM with a ratio of 2 to 1. Thus, the two functions are assigned weights of ⅔ and ⅓, respectively, to compute the overall availability of each expert. It is noted that the parameters in a weighted function typically add up to 1. This yields the following function:
 
 f   A,overall ( t )=⅔ *f   A,cellPhone ( t−t   cellphone )+⅓*( t−t   IMclient )=50/(3*( t−t   cellPhone )+75)+10/(3*√{square root over (t−t IMclient )}+30)
 
     At 10:05 AM, the overall presence/availability level of A is therefore 0.4091. If all other experts in U have presence/availability levels lower than 0.4091, then the expert locator application will select A at this time. A&#39;s presence level at 10:05 AM is higher on her IM client than her mobile phone according to the functions f A,cellPhone  and f A,IMclient . The expert locator application might thus try to reach A on her IM client first despite the locator&#39;s preference for voice or might indeed try to reach A on her mobile phone first. This discussion, however, is beyond the scope of the presence/availability level computation. 
     Presence Agent 
     As previously indicated, the presence agent  400  is a software entity that communicates with the presence server  500  over the network  150 . The network connection need not be a direct one, i.e., the data connection does not necessarily terminate at the presence server  500 . Intermediaries may be present and the presence agents  400  can connect to the presence server  500 , for example, through a gateway or proxy; via a database, shared file, or shared memory from where the presence server  500  picks up presence events from presence agents  400 ; or via an application that performs some type of preprocessing or filtering on presence events. For the sake of illustration, it is assumed that the presence agent  400  is connected to the presence server  500  without any intermediate proxy or system. 
     The presence agent  400  can be deployed on any commercially available mobile phone  110  that can execute the presence agent  400  and allow the presence agent  400  to intercept all button presses or can notify the presence agent  400  of button presses. The presence agent  400  can be deployed, for example, on a device  110  that executes the Symbian operating system or another embedded operating system. As previously indicated, an alternate embodiment of the present invention allows the functionality of the presence agent  400  to be implemented on one or more nodes in the network  150 . 
       FIG. 4  is a flow chart describing an exemplary implementation of the software agent process  400 . Generally, when the user powers up the mobile phone  110 , the software agent  400  is launched automatically and establishes a data connection to the presence server  500 . The first exchange of data over this connection indicates to the presence server  500  that the mobile phone  110  has been powered up and includes, for example, the telephone number and potentially other parameters, such as a user name. 
     The presence agent  400  can strive to maintain the data connection until the user turns off the mobile phone  110  or can tear down the data connection after each data exchange with the presence server  500  and then re-establish the connection before the next data exchange. In the latter case, a periodic data connection re-establishment can optionally be employed even in the absence of presence events on the mobile phone  110 , as a heartbeat signal to the presence server  500 . 
     As shown in  FIG. 4 , a test is performed during step  410  to determine if a powering up or down of the phone device  110  is detected. If it is determined during step  410  that a powering up or down of the phone device  110  has been detected, then the macropresence event is reported to the presence server  500  during step  420 . 
     Similarly, a test is performed during step  430  to determine if a button press is detected. As previously indicated, the presence agent  400  reports button presses and other events on the mobile phone  110  to the presence server  500 . The presence agent  400  may include, for example, an indication of the pressed button, as well as the mobile phone&#39;s phone number and potentially other parameters in the ensuing data exchange with the presence server  500 . As discussed below in conjunction with  FIG. 6 , the presence server  500  will record the time of the button press in the user&#39;s micropresence information. In the special case of the user pressing the power button (to power off the phone), the presence server  500  will also update the macropresence of the user. 
     In order to prevent flooding the presence server  500  with micropresence presence events from mobile phones  110 , the presence agent  400  can optionally propagate button presses or other events related to micropresence only if the last such button press or event was more than t ƒ  time units ago where t ƒ  is a configurable parameter. To this end, the presence agent must store the time t l  of the last macro/micropresence event on the phone. 
     Thus, if it is determined during step  430  that a button press (or another event) has been detected, then a further test is performed during step  440  to determine if the time, t l , since the last reported micropresence event exceeds the threshold, t ƒ . If it is determined during step  440  that the threshold has not been exceeded then there is no need to report the current micropresence event. If, however, it is determined during step  440  that the threshold has been exceeded then the current micropresence event is reported to the presence server  500  during step  450 . In this manner, when a micropresence event occurs, the presence agent  400  compares the current time t c  with t l  and propagates the event to the presence server if the difference between t c  and t l  exceeds the threshold, t f . If t f  is set to zero, the presence agent reports every micropresence event. Setting t f  to zero might be desirable for reporting purposes, advanced queries from presence subscribers, and with few mobile phones  110  connected to the presence server  500 . 
     Presence agents may also periodically recompute the values f u,s  with a configurable frequency to determine whether the user must be prompted for a presence and availability status update. A test is thus optionally performed during step  460  to determine if one or more functions f u,s  falls below a configured threshold, t s  (i.e., if the value of f u,s  at this time is smaller than the configurable threshold t s ). If it is determined during step  460  that the value of f u,s  falls below the threshold, t s , the presence agent  400  will prompt the user during step  470  for a presence/availability status update. 
     In an alternate implementation where the presence server  500  requests the prompting, the presence server  500  can monitor the functions f u,s  and if the presence server detects that the value of f u,s  for a given user u and presence source s has fallen below the configurable threshold t s , the presence server  500  can send a signal to the presence agent  400  connected to the presence source s. 
     In either implementation, the presence agent  400  can then prompt the user u for a presence and availability update on the presence source s, for example, by playing a sound or displaying a message on the telephone display. The user may respond, for example, by pressing an arbitrary button on the phone  110 . The button press constitutes a micropresence event that the presence agent  400  propagates to the presence server  500 . If the user does not respond to the prompting, the user can be prompted again. The reprompting should occur with a low frequency f p , for example on the order of tens of minutes. It is noted that if the user does not respond to the prompting, the presence server (or the presence agent, depending on the implementation) will determine with frequency f p  that the value of the function f u,s  is below the threshold t s . If the communication overhead of sending prompting signals from the presence server  500  to the agents  400  is considered too high, it is preferred that the agents  400  themselves recompute the values of f u,s  and perform the user prompting, when necessary, in the manner shown in  FIG. 4 . Otherwise, centralized computation of the values of f u,s  by the presence server  500  is preferred. 
     Presence Server 
       FIG. 5  is a schematic block diagram of an exemplary presence server  500 . The presence server  500  comprises a computer system that optionally interacts with media  550 . The presence server  500  comprises a processor  520 , a network interface  525 , a memory  530 , a media interface  535  and an optional display  540 . Network interface  525  allows the presence server  500  to connect to the network  150 , while media interface  535  optionally allows the presence server  500  to interact with media  550 , such as a Digital Versatile Disk (DVD) or a hard drive. Optional video display  540  is any type of video display suitable for interacting with a human user of the presence server  500 . Generally, video display  540  is a computer monitor or other similar video display. 
     As shown in  FIG. 5  and discussed further below in conjunction with  FIGS. 6 and 7 , respectively, the exemplary memory  530  stores a presence information maintenance process  600  and a presence information request process  700 . For a discussion of suitable techniques for processing such presence information, see, for example, U.S. patent application Ser. No. 10/672,633, entitled “Method and Apparatus for Delivering a Voice Mail Message With an Indication of the Presence of the Sender,” or U.S. patent application Ser. No. 10/672,635, entitled “Programmable Presence Proxy for Determining a Presence Status of a User,” each assigned to the assignee of the present invention and incorporated by reference herein. 
       FIG. 6  is a flow chart describing an exemplary implementation of a presence information maintenance process  600  incorporating features of the present invention. As shown in  FIG. 6 , the presence information maintenance process  600  initially performs a test during step  610  to determine if a macro or micro presence event has been received from a presence agent  400 . If it is determined during step  610  that a macro or micro presence event has been received from a presence agent  400 , then the event is recorded during step  620  including a time stamp. 
     A test is performed during step  630  to determine if the time since the last received heartbeat signal exceeds a threshold of n intervals. If the presence server  500  does not receive the heartbeat for n consecutive intervals, where n is a configurable parameter, the presence server  500  will consider the macropresence of this user to have ended during step  640 . This heartbeat mechanism addresses situations where the connection is lost due to, for example, dropped mobile phone signals, software errors and hardware problems with the phone (including a drained battery). These are cases where the likelihood is large that the user indeed cannot be reached on his or her mobile phone. In the case of a permanent data connection between the presence agent  400  and the presence server  500 , unavailability of the user due to events such as those mentioned above will result in the termination of the data connection, which the presence server  500  can interpret as the end of the macropresence of the user. 
     A further test is performed during step  650  to determine if the time since the last computation of the fuzzy presence functions, f u,s , exceeds a threshold, 1/f p . If it is determined during step  650  that the time since the last computation of the fuzzy presence functions, f u,s  exceeds the threshold, 1/f p , then the fuzzy presence functions, f u,s , are recomputed and cached during step  660 . 
     Assuming that there is a high frequency of presence queries against the fuzzy presence values of users, such a periodic recomputation and caching of the fuzzy presence of users can be performed with the configurable frequency of f p  by the presence server  500 . Typically, the recomputation will take place no more often than once in a few minutes. For each user, the presence server  500  stores at a minimum the time of the last presence event from that user&#39;s mobile phone  110 . If storage capacity is not an issue, the type of event (“power on”, type of button last pressed, “power off”, “missed heartbeat” or “data connection terminated”, etc.) should also be stored, as well as a log of past presence events for the purpose of reporting and enabling presence queries that include the history of user presence. 
     An example of the latter would be “find all users with phone numbers in the 908 area code who were present between 2 PM and 4 PM today and checked their call logs during that time”. After each interval of 1/f p  time units, the presence server  500  recomputes f u,s  for each user u and each of u&#39;s presence sources s using the difference between the current time and the time of the last presence event from s for u as the input for f u,s . 
     Additional computations such as that of f(U) that aggregate values of f u,s  for different presence sources and users, in the manner described above, may be performed by the presence information request process  700 , shown in  FIG. 7 , at the time of a presence query from a presence subscriber. Typically, there is a large number of aggregations that queries may request and thus pre-computing their values is likely to be wasteful if only a small subset of such aggregations is requested on a regular basis. If, however, a small known subset of aggregations is requested regularly, their values may be computed and cached at the times of the periodic recomputation of the f u,s  values instead of performing on-demand computations of these aggregations. If the expected frequency of presence queries is small, an on-demand computation and caching can be performed of the f u,s  values as well as of the aggregations. 
       FIG. 7  is a flow chart describing an exemplary implementation of a presence information request process  700 . As shown in  FIG. 7 , the presence information request process  700  initially computes the presence function f u,s (d) for each presence source during step  710 . Thereafter, the presence information request process  700  sorts the computed f u,s (d) functions during step  720  and then selects, during step  730 , the first presence source in the sorted list as the presence source where user u is most likely to be present and available. 
     Proxy Presence 
     The presence of a user refers to the physical presence of the user at a device, application, computer or system, generally at a given time and in a certain location. The user presence is of interest as an indication of where a user is or was at a certain time, what activity the user is or was engaged in, and how to currently reach this user with a communication. The user is seen as an actor (in the sense of being active) and as a subject. However, the user can also be viewed as an object of business and personal processes in which application-dependent representations of the user are processed. For example, a user&#39;s loan application in a bank business process represents the user, and the bank business process is doing something to the user&#39;s representation in a loan application by processing it. The user behind that loan application becomes the object of the bank business process. In another example, the user&#39;s contact information and address might get added to an electronic address book by another user. The former user becomes the object of the latter user&#39;s personal process of adding somebody to the address book, and the former user&#39;s contact information and address constitute that user&#39;s representation from the point of view of this personal process. 
     In both examples, the user&#39;s representation is present in the process in question for as long as the process is working on the user&#39;s representation. This type of presence is referred to as proxy presence and the representation of the user becomes a proxy presence source. The beginning and end of a proxy presence interval, i.e., the macro proxy presence, of a user, as well as the micro proxy presence, has to be determined in an application-specific manner. 
     Proxy presence may be interesting to various proxy presence subscribers for a variety of reasons. The user himself might be interested in his loan application proxy presence. For example, a customer service branch of a bank could employ the proxy presence techniques described herein to notify the user when the bank business process begins and ends processing the loan application. The beginning and end of the loan application can be considered the user&#39;s macro proxy presence whereas each major step or event along the way in the loan processing can be considered a micro proxy presence event. An example of the latter is a review, access or update of the loan application by a loan officer, or when an appraisal is performed in conjunction with the loan application. 
     Similarly, in an insurance company, an insurance policy, such as a life, car, home or umbrella policy, can be considered as a proxy representation of the user. Since a policy is typically a long-lived proxy presence source, the macro presence interval may be defined as the time that passes between the beginning of an insurance process that operates on the policy and the end of this process. If the insurance process has an extended duration, micro proxy presence can be introduced for policies as events that touch upon the processing of the policy. For example, retrieving the policy and reviewing the clauses of the policy by a claims adjustor could be considered micro proxy presence events. A proxy presence subscriber may want to identify the 5% least “proxy present” users for a new marketing campaign. A different proxy presence subscriber might be interested in all currently proxy present users so that it can send status updates for these users&#39; insurance policies. 
     Users might be curious about the proxy presence of their contact information in the electronic address books of friends or colleagues. The proxy presence subscriber client might periodically request a proxy presence update from the proxy presence server and notify the user when a friend has terminated his or her proxy presence. 
     The concepts of presence aging and fuzzy presence, as discussed above, apply to proxy presence sources under certain circumstances, as would be apparent to a person of ordinary skill in the art. Thus, the presence aging and fuzzy presence techniques described above can be employed to rank proxy presence events, originating at all proxy presence event sources, according to the timeliness of the proxy presence events. 
     As previously indicated, to determine real presence, presence agents  400  are deployed on or in conjunction with user devices  110 , such as personal computers, mobile phones, or applications. To determine proxy presence, the applications and systems that contain user representations have to either contain proxy presence agents  400  as integral parts or they have to give proxy presence agents  400  access to proxy presence. In either implementation, the same options that apply to connecting real presence agents  400  to real presence servers  500  are valid for connecting proxy presence agents with proxy presence servers. 
     If an application or system does not contain proxy presence agents  400  as integral parts, access to external proxy presence agents  400  can be provided in many different ways. For example, access to external proxy presence agents can be provided (i) through databases, shared files, or shared memory, from which proxy presence agents  400  retrieve changes in proxy presence information (in the case of a database, the proxy presence agent  400  can be built around a database trigger that gets invoked when the content of a proxy presence table changes, as discussed below in conjunction with  FIG. 8 ); (ii) by pushing proxy presence changes to proxy presence agents  400  via data connections, for example, by a node in a business workflow sending a notification of a proxy presence event to a proxy presence agent  400 ; or (iii) by allowing a proxy presence agent to periodically poll the application for proxy presence changes. For a detailed discussion of suitable techniques for adding such communication tasks to a workflow, see U.S. patent application Ser. No. 10/955,918, entitled “Method and Apparatus for Providing Communication Tasks in a Workflow,” incorporated by reference herein. 
     If a proxy presence agent  400  is given access to complete knowledge of every user&#39;s proxy presence, fuzzy proxy presence is not a particularly meaningful concept, and discrete proxy presence states, such as “present” or “not present” can be employed. Otherwise, fuzzy proxy presence may be computed in analogy to fuzzy real presence. 
       FIG. 8  is a sample table for an exemplary database trigger database  800  that records one or more database triggers that can be used to report presence events to a proxy presence agent  400  of a user. The exemplary database triggers in the sample database  800  are based on the loan application example discussed above. 
     Such database triggers provide a mechanism for a service provider, such as a bank, to notify a proxy presence agent  400  of presence events, such as macropresence and micropresence events. The loan process is considered a proxy presence source, in the manner described above for real proxy events. Generally, as the service provider logs information in a database, one or more database triggers executing on the database server can monitor the recorded information for presence related information that should be reported to a proxy presence agent  400 . A database trigger is typically comprised of three parts:
         1. a description of triggering events, such as database inserts, updates, or deletes (for example, a triggering event may be that a given user&#39;s loan application record has been updated in the database);   2. one or more conditions that describe restrictions on the triggering events (the conditions must evaluate to TRUE to allow the trigger to proceed to part 3; for example, the conditions may require that the given user&#39;s loan application record in the database has a new entry in the “status” column that says either “accepted” or “rejected”);   3. an action expressed as code (embodied, for example, as code in a database-centric programming language that can call external programs, such as a proxy presence agent  400  and send data to that external program; because database-centric programming languages are typically too restrictive to allow coding a proxy presence agent  400 , the proxy presence agent  400  would typically be an external program rather than the trigger itself).       

     System and Article of Manufacture Details 
     As is known in the art, the methods and apparatus discussed herein may be distributed as an article of manufacture that itself comprises a computer readable medium having computer readable code means embodied thereon. The computer readable program code means is operable, in conjunction with a computer system, to carry out all or some of the steps to perform the methods or create the apparatuses discussed herein. The computer readable medium may be a recordable medium (e.g., floppy disks, hard drives, compact disks, or memory cards). Any medium known or developed that can store information suitable for use with a computer system may be used. The computer-readable code means is any mechanism for allowing a computer to read instructions and data, such as magnetic variations on a magnetic media or height variations on the surface of a compact disk. A computer-readable storage medium or device expressly excludes transitory signals per se and transitory mediums such as carrier waves, wires, cables, fiber optics, infrared media, and the like. 
     The computer systems and servers described herein each contain a memory that will configure associated processors to implement the methods, steps, and functions disclosed herein. The memories could be distributed or local and the processors could be distributed or singular. The memories could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term “memory” should be construed broadly enough to encompass any information able to be read from or written to an address in the addressable space accessed by an associated processor. With this definition, information on a network is still within a memory because the associated processor can retrieve the information from the network. 
     It is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.