Context Services: .NET Context Framework

The application is the client using contextual data provided by the framework. It accesses the contextual data through the context programming model, i.e., the context API. The API separates the consumer of context data from the provider of contextual data.

The context programming model allows application to access the contextual data stored in the context repository. This is done through context classes, providing a semantic interpretation of a context. A context class maps the “meaning” of some context (i.e., context interpretation) to the physical data (i.e., “context representation”). For example, a representation for temperature data might be a double while the context class applies the semantic interpretation of “Celsius” to this data. Conceptually, several context classes can be active on the same context representation data at the same time, thus, providing different interpretations of the same data.

The Context repository maintains all known context instances and allows access to this data through a query language which resembles part of the functionality of SQL but with an event driven approach. A query is used to select the “interesting” context set from the available context sources; it does not filter directly on context representation instances. The selected contexts are then associated with their default context interpretation and exposed as a context collection by the context programming API to the application.

Filling the context repository is done by context providers monitoring the environment and updating associated contextual data through the context generation framework, a layer which separates a context providers from the context repository. The context generation layer defines a context generation API that allows context providers to push changes of a context’s state to the context repository which operates on context descriptors. When a context provider detects a context change, it creates a so called context descriptor which comprises among other data the context representation of the context’s now current state.

A context provider is not limited to monitoring physical context sources but can use already computational available data as well. For example, a free/busy context provider may use a resource planning system to monitor the availability of meeting rooms or utilize the user’s mailbox to gather other peoples’ whereabouts to update the availability status.

System Requirements

The context framework is compatible with the following versions of the .NET framework

• .NET 2.0
• .NETCF 2.0 (for mobile devices)

Note that not all context providers are natively available on all platforms due to hardware constraints. However, any context can be accessed through the networking functionality provided by the framework.

Maturity Level (?)