A Relational Approach to Querying Streams

Data streams are long, relatively unstructured sequences of characters that contain information such as electronic mail or a tape backup of various documents and reports created in an office. This paper deals with a conceptual framework, using relational algebra and relational databases, within which data streams may be queried. As information is extracted from the data stream, it is put into a relational database that may be queried in the usual manner. The database schema evolves as the user’s knowledge of the content of the data stream changes. Operators are defined in terms of relational algebra that can be used to extract data from a specially defined relation that contains all or part of the data stream. This approach to querying data streams permits the integration of unstructured data with structured data. The operators defined extend the functionality of relational algebra, in much the same way that the join does relative to the basic operators-select, project, union, difference, and Cartesian product.