Incorporating constraints in probabilistic XML

Constraints are important, not only for maintaining data integrity, but also because they capture natural probabilistic dependencies among data items. A probabilistic XML database (PXDB) is the probability subspace comprising the instances of a p-document that satisfy a set of constraints. In contrast to existing models that can express probabilistic dependencies, it is shown that query evaluation is tractable in PXDBs. The problems of sampling and determining well-definedness (i.e., whether the aforesaid subspace is nonempty) are also tractable. Furthermore, queries and constraints can include the aggregate functions count, max, min, and ratio. Finally, this approach can be easily extended to allow a probabilistic interpretation of constraints. Categories and Subject Descriptors: H.2.1 [Database Management]: Logical Design--Data models; H.2.4 [Database Management]: Systems--Query processing; G.3 [Mathematics of Computing]: Probability and Statistics General Terms: Algorithms Additional Key Words and Phrases: Probabilistic databases, probabilistic XML, constraints, sampling probabilistic data