We propose a more general form of functional dependency for semantic data models that derives from their common feature in which the separate notions of domam and relation m the relational model are combined into a single notion of class. This usually results in a richer terminological component for their query languages, whereby terms may navigate through any number of properties, including none. We prove the richer expressiveness of thm more general functional dependency, and exhibit a sound and complete set of inference axioms Although the general problem of decidability of their logical implication remains open at this time, we present decision procedures for cases in which the dependencies included in a schema correspond to keys, or m which the schema itself is acyclic. The theory is then extended to include a form of conjunctive query. Of particular sigmficance is that the query becomes an additional source of functional dependency. Finally, we outline several applications of the theory to various problems in physical design and in query optimization.The applications derive from an ability to predict when a query can have at most one solution.

Many keyword queries issued to Web search engines target information about real world entities, and interpreting these queries over Web knowledge bases can often enable the search system to provide exact answers to queries. Equally important is the problem of detecting when the reference knowledge base is not capable of answering the keyword query, due to lack of domain coverage.In this work we present an approach to computing structured representations of keyword queries over a reference knowledge base. We mine frequent query structures from a Web query log and map these structures into a reference knowledge base. Our approach exploits coarse linguistic structure in keyword queries, and combines it with rich structured query representations of information needs.

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We investigate whether identification constraints such as keys and functional dependencies can be granted full status as concept constructors in a Booleancomplete description logic. In particular, we show that surprisingly simple forms of such constraints lead to undecidability of the associated logical implication problem if they are allowed within the scope of a negation or on the left-hand side of inclusion dependencies. We then show that allowing a very general form of identification constraint to occur in the scope of monotone concept constructors on the right-hand side of inclusion dependencies still leads to decidable implication problems. We consider the relationship between certain classes of identification constraints and nominals.