Describing Data Sources
In order for a data integration system to process a query over a set of data sources, the system must know which sources are available, what data exist in each source, and how each source can be accessed. The source descriptions in a data integration system encode this information. In this chapter we study the different components of source descriptions and identify the trade-offs involved in designing formalisms for source descriptions.
To put the topic of this chapter in context, consider the architecture of a data integration system, redrawn in Figure 3.1. Recall that a user (or an application) poses a query to the data integration system using the relations and attributes of the mediated schema. The system then reformulates ...