Grant E. Weddell

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A fundamental problem in Description Logics (DLs) is satisfiability, the problem of checking if a given DL terminology T remains sufficiently unconstrained to enable at least one instance of a given DL concept C to exist. It has been known for some time that lazy unfolding is an important optimization technique in model building algorithms for(More)
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 <italic>domain</italic> and <italic>relation</italic> in the relational model are combined into a single notion of <italic>class</italic>. This usually results in a richer terminological component for their(More)
Automated extraction of structured data from Web sources often leads to large heterogeneous knowledge bases (KB), with data and schema items numbering in the hundreds of thousands or millions. Formulating information needs with conventional structured query languages is difficult due to the sheer size of schema information available to the user. We address(More)
Virtually all semantic or object-oriented data models assume objects have an identity separate from any of their parts, and allow users to define complex object types in which part values may be any other objects. This often results in a choice of query language in which a user can express navigating from one object to another by following a property value(More)
We investigate whether identification constraints such as keys and functional dependencies can be granted full status as concept constructors in a Boolean-complete 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(More)