Victor M. Markowitz
Abstract
A common approach to database design is to describe the structures and constraints of the database application in terms of a semantic data model, and then represent the resulting schema using the data model of a commercial database management system. Often, in practice, Extended Entity-Relationship (EER) schemas are translated into equivalent relational schemas. This translation involves different aspects: representing the EER schema using relational constructs, assigning names to relational attributes, normalization, and merging relations. Considering these aspects together, as is usually done in the design methodologies proposed in the literature, is confusing and leads to inaccurate results. We propose to treat separately these aspects and split the translation into four stages (modules) corresponding to the four aspects mentioned above. We define criteria for both evaluating the correctness of and characterizing the relationship between alternative relational representations of EER schemas.
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Index Terms
- Representing extended entity-relationship structures in relational databases: a modular approach
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Reviews
Morteza Parang
The authors present an improved approach to common database design methodologies that involve translation of the applications semantic model to a relational schema. They point out that many of these common methods (for example, the extended entity-relationship (EER) model) include several aspects that can be confusing and in practice often lead to inaccurate results. The authors propose a modular approach to the translation of EER schemas into relational schemas. Their proposed approach separates the translation process into four stages: (1) translating EER schemas into canonical relation schemas, (2) assigning names to relational attributes, (3) normalizing relational schemas representing EER schemas, and (4) merging relational schemas in relation schemas representing EER schemas. This approach takes into account two key points: inclusion dependencies and null constraints, and appropriate name assignments for relational attributes. Based on the above, the authors examine alternative equivalent relational representations for EER schemas and show that EER translation and normalization can be combined without restricting or restructuring the original EER schema. The paper does not claim to address the complex issues related to the interpretation of the real-world informational meaning represented by an EER. Therefore, within the constraint inherent in the accuracy and meaning of the semantic data model, the authors approach is an improvement to the traditional database design. The paper is well written, concise, and understandable to a wide circle of database designers and researcher s. While it may be too long for researchers in the field, its many examples are a good tutorial feature. The references cited are complete and satisfactory for the scope of the paper.
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