View Integration and Cooperation in Databases, Data Warehouses and Web Information Systems

View integration aims at replacing a set of existing views by a single new one in such a way that with respect to information capacity the new view dominates or is equivalent to the old ones. Therefore, in this article we first investigate a theory of schema equivalence and dominance for the higher-order Entity-Relationship model (HERM) based on the notion of computable queries. We then develop formal transformation rules for schema integration that are embedded in a pragmatic method telling how they should be applied for integration.

We then apply the approach to views, which occur as the basic constituents for user interfaces as formalised by the notion of dialogue type. In two follow-on steps we apply the rule-based view integration technique to data warehouses and web information systems. In the case of data warehouses the fundamental idea is the separation of input from operational databases and output to on-line analytical processing (OLAP) systems. Both the extraction of data from the operational databases and the definition of the data-marts for OLAP can be formulated by views.

In the case of web information systems, views form the core of media types, which provide abstract means for describing content, functionality, context and adaptivity to user preferences and intentions, end-devices, and channel limitations. In this case the queries defining the views must be highly expressive, as they must involve the creation of abstract identifiers, complex values and links. We extend the transformation rules to cope with these requirements.

View cooperation provides an alternative to view integration in which the integrated view is only virtual. That is the constituting views are kept and exchange functions are designed to provide the same functionality as if the views were integrated.