An Adaptable Approach for Integrity Control in Federated Database Systems

In database federations the integrity problem arises from the degree of heterogeneity and autonomy of participating component database systems. This causes integrity control more complicate than that in traditional centralized database systems. Semantic integrity should be considered in two phases: constraint federation and constraint enforcement. Otherwise, the administrators of component database systems might not agree to join the federation, or some or even all of component databases will be in an inconsistent state when an update is executed. The semantic integrity of federated database refers to representation integrity and enforcement integrity. The representation integrity means that the constraint definition of federated database schema should correctly reflect the characteristics of schema integration. The enforcement integrity means that the federated database state should be consistent with constraints defined over it, when an update is executed. In this thesis, we propose a new component to keep the semantic integrity of federated database. Firstly, we specify an integrity control component, which plays an extendible part of an FDBMS. A set of modules within a reference architecture is given; different degrees of evaluation autonomy are distinguished; and coupling principle is developed to unravel conflicts between the evaluation state of component constraints and that of global ones. Secondly, we develop integrity control enforcement policies for the federation policy. We show that this model is adaptable and flexible to represent the characteristics of federation and the application requirements of constraint enforcement plan. Thirdly, we define an integrity constraint type model that acts as a canonical model. It represents component constraints as integrity constraint types. Based on this model, federation users can translate component constraints, then integrate them and form global ones. These two models, taken together, preserve the representation integrity at the constraint federation phase. Fourthly, we give a two-step approach to enforce constraints. This approach is made up of two parts: type-based two-phase evaluation and policy-based two-phase commitment. It maintains the enforcement integrity at the constraint enforcement phase. Finally, the feasibility of the proposed component is implemented in a prototype, called MIGI. Spatial constraint federation and spatial constraint enforcement have been taken into account in MIGI.