Data constraints are used in structured and unstructured databases to capture real-world semantics observed in the modeled application domain. In our context, a constraint can be defined as a set of predicates P
∧ ... P
. Each predicate is in the form C
, where C
is an attribute,
is a comparison operator and C
is either an attribute or a constant . Constraints are assertions on permissible or consistent database states, and specify certain properties of data that need to be satisfied by valid instances of the database.