Real-scale Semantic Web applications, such as Web Portals and E-Marketplaces, require the management of voluminous metadata repositories containing descriptive information (i.e., metadata) about the available Web resources and services. Better knowledge about the meaning, usage, accessibility or quality of these resources and services will considerably facilitate the automated processing of both Web content and services. In this context, the Resource Description Framework (RDF) enables the creation and exchange of metadata as any other Web data. Although large volumes of RDF descriptions are already appearing (e.g., as exported Portal catalogs or service descriptions), sufficiently expressive declarative languages for querying both RDF descriptions and schemas are still missing. In this paper, we propose RQL, a new RDF query language, relying on a formal graph model that permits the interpretation of superimposed resource descriptions. RQL is an OQL-inspired adaptation of XML query languages to the peculiarities of RDF but, foremost, is an extension of this functionality for uniformly querying both descriptions and schemas. We illustrate the syntax, semantics and core functionality of RQL bymeans of a set of benchmark queries and report on the performance of RSSDB, our persistent RDF Store, for storing and querying voluminous RDF descriptions.

The creation of a complex web site is a thorny problem in user interface design. In this paper we explore the notion of adaptiveweb sites: sites that semi-automatically improve their organization and presentation by learning from visitor access patterns. It is easy to imagine and implementweb sites that offer shortcuts to popular pages. Are more sophisticated adaptiveweb sites feasible? What degree of automation can weachieve? To address the questions above, we describe the design space of adaptiveweb sites and consider a case study: the problem of synthesizing new index pages that facilitate navigation of a web site. We presentthePageGather algorithm, which automatically identifies candidate link sets to include in index pages based on user access logs. We demonstrate experimentally that PageGather outperforms the Apriori data mining algorithm on this task. In addition, we compare PageGather's link sets to pre-existing, human-authored index pages.

The management of semistructured data has recently received significant attention because of the need of several applications to model and query large volumes of irregular data. This paper considers the problem of query containment for a query language over semistructured data, StruQL0 , that contains the essential feature common to all such languages, namely the ability to specify regular path expressions over the data. We show here that containment of StruQL0 queries is decidable. First, we give a semantic criterion for StruQL0 query containment: we show that it suffices to check containment on only finitely many canonical databases. Second, we give a syntactic criteria for query containment, based on a notion of query mappings, which extends containment mappings for conjunctive queries. Third, we consider a certain fragment of StruQL0 , obtained by imposing restrictions on the regular path expressions, and show that query containment for this fragment of StruQL0 is NP complete. 1 ...

The need for descriptive information, i.e., metadata, about Web resources has been recognized in several application contexts (e.g., digital libraries, infomediaries, portals, etc.). The Resource Description Framework (RDF) aims at facilitating the creation and exchange of metadata, as any other Web data. In particular, the definition of schema vocabularies enables the interpretation of RDF descriptions across several communities.

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The creation of a complex web site is a thorny problem in user interface design. In this paper we explore the notion of adaptiveweb sites: sites that semi-automatically improve their organization and presentation by learning from visitor access patterns. It is easy to imagine and implementweb sites that offer shortcuts to popular pages. Are more sophisticated adaptiveweb sites feasible? What degree of automation can weachieve? To address the questions above, we describe the design space of adaptiveweb sites and consider a case study: the problem of synthesizing new index pages that facilitate navigation of a web site. We presentthePageGather algorithm, which automatically identifies candidate link sets to include in index pages based on user access logs. We demonstrate experimentally that PageGather outperforms the Apriori data mining algorithm on this task. In addition, we compare PageGather's link sets to pre-existing, human-authored index pages. Keywords: adaptive, cluste...