## 2 Analysis of the State of the Art
### 2002, [PERSON] _et al._  
The approach followed by [PERSON] _et al_. [49] makes the following notes about context in pervasive environments:  
* Context information exhibits temporal characteristics. Context can be static (those characteristics that do not change over time, e.g., birthday) or dynamic, e.g., user location. Besides, the persistence of the dynamic information can easily change. This way, it is justified that the static context should be provided by the user, while the dynamic one should be gathered by sensors. Past historic and a possible future context are also taken into account as part of the description of the whole context description. * A second property of the context information is its imperfection. Information can be useless if it cannot reflect a real world state. It also can be inconsistent if it contains contradictions, or incomplete if some context aspect are unknown. There are many causes to these situations. For example, information can change so fast that it may be invalid once it is collected. This is obviously because the dynamic nature of the environment. Besides, there is a strong dependency on software and hardware infrastructures, which can fail any time. * Context has multiple alternative representations. Context information usually comes from sensors which \"speak\" different languages. For example, a location sensor can use latitude and longitude metrics while the involved application works with a street map. * Context information is highly disassociated. There are obvious connections between some context aspects, e.g., users and devices. However, other connections need to be computed with the available information. This work also indicates the dependency between context models, the scenarios and use cases of the application domains. Authors extract several context parameters to consider:  
* User activity, distinguishing between the current one and the planned one. * Device that is being used by the user. * Available devices and resources. * Current relationships between people. * Available communication channels. ### 2002, [PERSON] _et al._  
In 2002, [PERSON] _et al_. [50] discuss about the necessity of content adaptation and representation formats for context information in dynamic environments. A significant perspective is the justification of modeling not only the user but the network status and device context information as well. The following parameters are considered as relevant context information:  
* Device: basic hardware features, e.g., CPU power, memory,..., user interface input, e.g., keyboard, voice recognition,... and output, e.g., display and audio, and other particular specifications of the device, e.g., display resolution, color capability,....
* User: service selection preferences, content preferences and specific information about the user. * Network connection: bandwidth, delay, and bit error rate. Authors also present several requirements concerning the representation of context information. Accordingly, they defend that a context profile should be:  
* Structured, to ease the management of the amount of gathered information and remark relevant data about the context. * Interchangeable, for components to interchange context profiles. * Composable/decomposable, to maintain context profiles in a distributed way. * Uniform, to ease the interpretation of the information. * Extensible, for supporting future new attributes. * Standardized, for context profile exchanges between different entities in the system. 2004, [PERSON] _et al._**: The SOCAM Ontology**  
In 2004 [PERSON] _et al_. [51] design the SOCAM service-oriented context-aware middleware architecture for designing and prototyping applications in an Intelligent Environment. following components:  
* Context providers, which abstract context information from heterogeneous sources and semantically annotate it according to the defined ontology. * The context interpreter, which provides logic reasoning to process information about the context.