## 2 Analysis of the State of the Art
### 2002, [PERSON] _et al._
* The context database, which stores current and past context ontologies. * Context-aware applications, which adapt their behavior according to the current context situation. * The service-locating service, which allows context providers and interpreters to advertise their presence for users and applications to locate them. [PERSON] _et al_. use OWL to describe their context ontologies in order to support several tasks in SOCAM. As the pervasive computing domain can be divided into smaller sub-domains, the authors also divided the designed ontology into two categories:  
* An upper ontology, which captures high-level and general context knowledge about the physical environment. * A low-level ontology, which is related to each sub-domain and can be plugged and unplugged from the upper ontology when the context changes. As a result, the upper ontology considers person, location, computational entity and activity as context concepts. [PERSON] _et al_. [52] also present an OWL based model to represent, manipulate and access context information in smart environments. The model represents contexts and their classification, dependency and quality of information using OWL to support semantic interoperability, contextual information sharing, and context reasoning. The ontology allows to associate entities' properties with quality restrictions that indicate the contextual information quality. 2005, [PERSON] _et al_. **: The CoBrA Ontology**  
Another work under a similar approach is the one performed by [PERSON] _et al_. [53]. Authors introduce the CoBrA ontology based system, which provides a set of semantic concepts for characterizing entities such as people, places or other objects within any context. The system provides support for context-aware platforms in runtime, specifically for Intelligent Meeting Rooms. The context broker is the central element of the architecture. This broker maintains and manages a shared context model between agents (applications, services, web services, _etc._) within the community. In intelligent environments participating agents often have limited resources and capabilities for managing, reasoning and sharing context. The broker's role is to help these agents to reason about the context and share its knowledge. The presented ontology relies on:  
* Concepts that define physical places and their spatial connections. * Concepts that define agents (humans and not humans). * Concepts that define the location of an agent. * Concepts that describe an agent activity. **2005, [PERSON] _et al._: The Citron Framework  
In 2005 [PERSON] _et al._[54] present a framework for personal devices which gathers context information about the user and his/her surrounding environment. Muffin, a personal sensor-equipped device is designed. Using it, several context parameters are gathered. Sensor information is also considered for evaluating several user high-level context information. For example, accelerometer readings might recognize a walking or running activity, shaking and rotating, _etc._ The microphone is not only used to measure the ambient noise. It is also useful for detecting the place where the user is, e.g., meeting room, restaurant, street,.... The context acquisition is categorized in two different groups: the user and the environment. For the user several issues are analyzed. For example, activities recognition requires the user to use the device in specific ways (it is not the same to use it with hands or waist-mounted). Another problem they encounter is about the time consuming process since an event is captured, then processed and finally validated. The last contextual issue deals with the intrinsic complexity and ambiguity of context information. For example, the meaning of what is loud might depend on the current situation, e.g., if the user is in a meeting room, if the user is in the street.... For the environment, Muffin suffer several heat problems due to the sensors sensitivity to environment temperature. This way, sometimes the gathered measures are invalid.