We investigate a class of path constraints that is of interest in connection with both semistructured and structured data. In standard database systems, constraints are typically expressed as part of the schema, but in semistructured data there is no explicit schema and path constraints provide a natural alternative. As with structured data, path constraints on semistructured data express integrity constraints associated with the semantics of data and are important in query optimization. We show that in semistructured databases, despite the simple syntax of the constraints, their associated implication problem is r.e. complete and nite implication problem is co-r.e. complete. However, we establish the decidability of the implication and nite implication problems for several fragments of the path constraint language, and demonstrate that these fragments su ce to express important semantic information such as extent constraints, inverse relationships and local database constraints commonly found in object-oriented databases.
Constraints on paths in semistructured databases are investigated in REF .
Path Constraints in Semistructured Databases
J. Comput. Syst. Sci.
Computer Science