Extending an ORDBMS: The StateMachine Module
نویسندگان
چکیده
Extensibility is one of the mayor benefits of object -relational database management systems. We have used this system property to implement a StateMachine Module inside an object-relational database management system. The module allows the checking of dynamic integrity constraints as well as the execution of active behavior specified with the UML. Our approach demonstrates that extensibility can effectively be applied to integrate such dynamic aspects specified with UML statecharts into an object-relational database management system. 1 Motivation Object-relational database management systems (ORD-BMS) enable us to extend their off-the-shelf functionality by self-developed extension modules [6]. This allows us to adopt an ORDBMS to the needs of several application domains. Our demonstration illustrates how this feature can be exploited to equip an ORDBMS with a module which handles dynamic aspects inside the database system. In our SERUM project [3], we use an object-oriented specification as an input to generate data storage components. Since UML [4] offers a rich set of object-oriented constructs and is widely used, we have chosen it as specification language. Class diagrams are used to describe the data structures, and the mapping of these structures to an object-relational schema is straightforward. Each class of the class diagram is mapped to a row type and a typed table in the database schema. Inheritance relationships can be mapped onto table inheritance (see [2] for details and problems with multiple inheritance). Methods declared in the class diagram are implemented as user-defined routines (UDRs) in the ORDBMS, and associations can be established in several ways, e.g., by using foreign keys. These mappings do not only apply to the SERUM context, but are a general approach when implementing an object-relation-al schema on the basis of an object-oriented specification. In addition, the capabilities of ORDBMSs allow to consider dynamic modelling aspects, too. UML statechart diagrams are an appropriate way to specify these aspects. In the context of ORDBMS-based data storage components, statecharts can be used for two purposes [5]: • Observing dynamic integrity constraints In contrast to static integrity constraints describing the correctness of a database state, dynamic integrity constraints restrict the transitions between different states. For this purpose, valid sequences of operations, pre-and post-conditions for transitions, and state-dependent invariants can be specified. Whenever such a constraint is being violated, the conflicting operation has to be prevented. • Implementing active behavior Statecharts can be used to specify functionality in form of actions which have to …
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