Local and global constraints in database integration

In supporting global updates in a distributed database system obtained by database integration, three key problems arise: (1) update translation, i.e. how to translate a global update into a corresponding set of local updates; (2) constraint integration, i.e. how to determine what constraints exist on the integrated global database and how to check and enforce them during global updates; and (3) transaction management, i.e. distributed concurrency control, commit, and recovery mechanisms. The constraint integration problem is dealt with in the context of the integration of relational databases using the 2-D union operator, a slightly modified form of the outer natural join. Given the local constraints that hold on the individual local databases, a method is developed for determining the constraints that hold on the integrated global database and for checking and enforcing constraints in a hierarchical fashion during global updates