Context is an essential element in mobile and ubiquitous computing. Users’ information needs can be better understood and supplied by means of context-awareness. Context data may be sensed, inferred, or directly input by users, and so forth, which calls for specific query mechanisms to acquire context information. On the other hand, traditional non-context-aware database querying techniques need to be re-examined, taking query context into account. In order to design effective context-aware database query processing mechanism, the authors survey the latest developed context-aware querying techniques in the data management field. They outline six ways to query context directly, and provide a categorization about how to use context in querying traditional databases. The approaches of handling imperfect context in context-aware database querying are also described. They discuss some potential research issues to be addressed at the end of the chapter.
To start the discussion, let us first look at two scenarios, which may occur in a mobile and ubiquitous computing environment.
Scenario 1. John is on a vocational trip and come to a city for the first time. He has a tour guide in his PDA, and the main function of this tour guide is to tell John where he is. When he wants to visit the museum, he uses the PDA to guide his way to museum. When he is visiting the museum, the PDA can provide the information of an exhibit when he comes close to the exhibit. Such a function needs to request location context information from a GPS provider or a RFID system.
The scenario involves querying context information. In many context-aware applications, context information acquisition is essential and should be considered before using context information. It is always necessary to provide sufficient support for context querying in context-aware applications because many operations and functions of the applications would be based on it.