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  • × author_ss:"Christophides, V."
  1. Abiteboul, S.; Cluet, S.; Christophides, V.; Milo, T.; Moerkotte, G.; Siméon, J.: Querying documents in object databases (1997) 0.00 
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    Abstract
    We consider the problem of storing and accessing documents (SGML and HTML, in particular) using database technology. To specify the database image of documents, we use structuring schemas that consist in grammars annotated with database programs. To query documents, we introduce an extension of OQL, the ODMG standard query language for object databases. Our extension (named OQL-doc) allows us to query documents without a precise knowledge of their structure using in particular generalzed path expressions and pattern matching. This allows us to introduce in a declarative langugae (in the style of SQL or OQL), navigational and information retrieval styles of accessing data. We also consider the interaction of full-text indexes (e.g. inverted files) with standard database collection indexes (e.g, B-trees) that provide important speed-up
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    a
  2. Christophides, V.; Plexousakis, D.; Scholl, M.; Tourtounis, S.: On labeling schemes for the Semantic Web (2003) 0.00 
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    Abstract
    This paper focuses on the optimization of the navigation through voluminous subsumption hierarchies of topics employed by Portal Catalogs like Netscape Open Directory (ODP). We advocate for the use of labeling schemes for modeling these hierarchies in order to efficiently answer queries such as subsumption check, descendants, ancestors or nearest common ancestor, which usually require costly transitive closure computations. We first give a qualitative comparison of three main families of schemes, namely bit vector, prefix and interval based schemes. We then show that two labeling schemes are good candidates for an efficient implementation of label querying using standard relational DBMS, namely, the Dewey Prefix scheme [6] and an Interval scheme by Agrawal, Borgida and Jagadish [1]. We compare their storage and query evaluation performance for the 16 ODP hierarchies using the PostgreSQL engine.

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