ULIXES: Building Relational Views over the Web

We consider structured Web sites, those sites in which structures are so tight and regular that we can assimilate the site, from the logical viewpoint, to a conventional database. We have argued that, with respect to structured Web servers, it is possible to apply ideas from traditional database techniques, specifically with respect to design, query, and update. Here we focus on the querying process, which consists in associating a scheme with a server and then use this scheme to pose queries in a high level query language. To describe the scheme, we use a specific data model, called the ARANEUS Data Model (ADM). We say that ADM is a page oriented model, in the sense that the main construct of the model is that of page scheme, used to describe the structure of sets of homogeneous pages in the server. ADM schemes are then offered to the user, who can query them by means of the ULIXES language, whose expressions produce relations as results. These are essentially relational views over Web data and can therefore be queried using any relational query language. It should be noted that our approach inherited some ideas from other recent proposals for query languages for the Web. However, these approaches are mainly based on a loose notion of structure, and tend to see the Web as a huge collection of unstructured objects, organized as a graph. In contrast, our approach explicitly considers structure, both in the infomation source (the Web) and in the derived information (the relational views).