Copyright 1998 INIST-CNRS CC BY 4.0 Sauf mention contraire ci-dessus, le contenu de cette notice bibliographique peut être utilisé dans le cadre d’une licence CC BY 4.0 Inist-CNRS / Unless otherwise stated above, the content of this bibliographic record may be used under a CC BY 4.0 licence by Inist-CNRS / A menos que se haya señalado antes, el contenido de este registro bibliográfico puede ser utilizado al amparo de una licencia CC BY 4.0 Inist-CNRS
Notes:
Computer science; theoretical automation; systems
Sciences of information and communication. Documentation
FRANCIS
Accession Number:
edscal.2036612
Database:
PASCAL Archive
Further Information
In some database applications it is natural to define individual attributes of a relation as derived attributes, separately from the definition of other attributes. This approach minimizes the complexity of the schema. We propose a formalism in which rules are divided into two classes: Defining rules specify the existence of tuples in the relation, together with some of their attributes. Refining rules specify derived attributes of tuples that already exist according to the defining rules. A potential problem with this approach is that view definitions may appear to be recursive, as some attributes of a relation are defined in terms of others. We show how this apparent recursion can be dealt with by identifying the attributes through which the recursion occurs. We present semantics based on these notions, and show how they allow the natural formulation of a motivating example. We discuss evaluation of rules with our semantics, demonstrating that goal-directed evaluation and incremental evaluation are possible, and that only rules defining derived attributes that are necessary for a query need to be evaluated in order to answer the query. Our proposal is directly relevant to the semantics of virtual columns in SQL3.
