Implementing a universal relation interface using access scripts with binding patterns

We propose the use of the universal relation as a user interface to provide transparent access to a network of distributed, heterogeneous, and autonomous information sources. We implement this interface in two layers. The lower layer consists of access scripts, which encapsulate knowledge about information sources and are capable of answering basic queries. The upper layer uses combinations of these scripts to answer user queries phrased in terms of a universal relation. Access scripts know how to obtain information either directly from sources or from service providers (mediators, traders, and the like). They present this information in relational form, but with an inherent direction, in the sense that whenever values for a fixed subset of attributes of the relation are given, the access script will deliver values for the rest of the attributes in the relation. In this paper, we address the problem of defining the semantics of a user query posed against the universal relation and of finding a sequence of access script invocations that gathers the information requested in the query