PARDES---an enhanced active database system (abstract)

摘要

Traditional databases are passive. They do only what isexplicitly requested in the user's query or update operation. Theactive database paradigm states that a database may react in anintelligent way to an external input by creating and executingdatabase operations, which, though not explicitly requested in theinput, are required to preserve invariants associated to the database.

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This paradigm replaces many operations traditionally implementedby application programs with descriptive definitions that are partof the database schema. Models and research prototypes based onthis paradigm are POST-GRES, HiPAC, SAPIENS, Ariel.

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Our model extends existing active database models in thefollowing ways:

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• It increases the expressive-power of the language used todefine the database schema by allowing the specification of aricher class of invariants than is currently supported. Example:(SALARY:=BASE-SALARY + BONUS + 1000^* count(SUBORDINATES)) The proposed language is compactyet powerful. Itreduces the cost of development and maintenance of database updateapplications and reduces the problems of validation andverification.rn
• It provides an efficient algorithm for generating the auxiliaryoperations required to preserve the invariants after an update (Inother models these operations have to be explicitly coded, eitherin the application program or in the database schema.)rn
• Our model introduces the notion of Exception-Handling Mode,proposes a number of such modes, and specifies how modes can bedefined in the data base schema. The modes we propose eliminate alarge portion of the exception handling code that currently existsin application programs.

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