View mappings for query languages

Wong, Kam Chooi (1984). View mappings for query languages. PhD thesis The Open University.



The problems of current use of query languages are looked at. One chief drawback is the undesirable requirement for end user familiarity with and knowledge of the underlying database structures, in order to retrieve data effectively. The approach adopted towards resolving this is by means of high-level view support, using unit view structures called perceived records. A prime concern of this thesis then, is the study of perceived record mappings from the database.

A set of criteria for categorising and analysing the features of database mappings for end-user views is first developed. In addition, a classification of data structure transformations and data item transformations is also presented. The framework is general and is independent of a specific data model or database management system. Its usefulness is demonstrated by its application to the analysis of view transformations from recursive database structures to high-level, unit view structures. In addition, it serves as a basis for evaluating and comparing the mapping facilities in existing systems.

Possible ways of specifying a suitable data model for the perceived record view concept are described. Following on, two general mapping techniques are discussed. This leads to a proposal for a mapping mechanism that supports the flexible derivation of complex perceived record views that can differ considerably from the source structures. The mechanism uses an intermediary canonical transform model. Description of how the transform model mechansim can be used in practical systems to derive perceived record views, is also presented.

The feasibility of the ideas proposed are tested out by implementing an interactive software system for defining perceived record views. For this, a mapping definition language for perceived record derivation is first designed. The control system sets up the structures of the mapping definition language and prompts the End-User-Administrator to define and specify the mappings for a perceived record. Appraisals of both the proposed mapping mechanism and implementation are discussed. Examples of use of the interface system are included. The limitations of the implementation are pinpointed with suggestions for further improvements. Practical applications of the work and evaluation of the approach in the light of other existing approaches, are also discussed.

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