Compositional algebra for interactive data access

An important issue for the success of a database application is the effecti veness of its interface. Frequently a relevant part of the programming effo rt is devoted to the generation of interfaces. The visual programming envir onments reduce only partly this effort, and in particular, things become mo re complicated when data coming from different sources (different views in the same database or even views from different databases or systems) are to be related and must cooperate in the data navigation and manipulation task . To overcome this problem we present a new database access paradigm based on an algebra on the domain of computational abstractions called "services" which include both dimensions: the data access computation and the user in teraction. This means that the interaction is not implemented by using sepa rated constructs as happens for traditional computational models; on the co ntrary, as the interaction is an integral part of the service paradigm, the user interaction is computed starting from the declarative specification o f the data access itself. The combination of services in a service expressi on through the operators defined by the service algebra makes it possible t o generate cooperating user interfaces for complex data navigation and mani pulation. Through algebraic properties, which hold both from the data and u ser interface point of view, the service expressions can be simplified and optimized guaranteeing their initial semantics. The paper shows the applica tion of the service algebra to the relational environment by means of a sim ple extension to SQL. Finally, the paper describes a tool based on a three tier architecture and on lava technology for developing and distributing se rvices in Web environment. Services and combination of services expressed w ith the service algebra are automatically translated into Java objects, all owing the rapid development of platform independent data access services. ( C) 2000 Published by Elsevier Science Ltd.