A LOGICAL VIEW OF STRUCTURED FILES

Structured data stored in files can benefit from standard database tec hnology. In particular, we show here how such data can be queried and updated using declarative database languages. We introduce the notion of structuring schema, which consists of a grammar annotated with data base programs. Based on a structuring schema, a file can be viewed as a database structure, queried and updated as such. For queries, we sho w that almost standard database optimization techniques can be used to answer queries without having to construct the entire database. For u pdates, we study in depth the propagation to the file of an update spe cified on the database view of this file. The problem is not feasible in general and we present a number of negative results. The positive r esults consist of techniques that allow to propagate updates efficient ly under some reasonable locality conditions on the structuring scheme s.