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Extracting the extended entity-relationship model from a legacy relational database

机译：从遗留关系数据库中提取扩展的实体关系模型

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摘要

The maintenance of an existing database depends on the depth of understanding of its characteristics. Such an understanding is easily lost when the developers disperse. The situation becomes worse when the related documentation is missing. This paper addresses this issue by extracting the extended entity-relationship schema from the relational schema. We developed algorithms that investigate characteristics of an existing legacy database in order to identify candidate keys of all relations in the relational schema, to locate foreign keys, and to decide on the appropriate links between the given relations. Based on this analysis, a graph consistent with the entity-relationship diagram is derived to contain all possible uniary and binary relationships between the given relations. The minimum and maximum cardinalities of each link in the mentioned graph are determined, and extra links within the graph are identified and categorized, if any. The latter information is necessary to optimize foreign keys related information. Finally, the last steps in the process involve~(when applicable) suggesting improvements on the original conceptual design, deciding on relationships with attributes, many-to-many and n-ary (n≥3) relationships, and identifying is-a links. User involvement in the process is minimized to the case of having multiple choices, where the system does not have the semantic knowledge required to decide on a certain choice.
机译：现有数据库的维护取决于对数据库特征的理解深度。当开发人员分散时，这种理解很容易丢失。如果缺少相关文档，情况将变得更糟。本文通过从关系模式中提取扩展的实体关系模式来解决此问题。我们开发了研究现有遗留数据库特征的算法，以便识别关系模式中所有关系的候选键，定位外键并确定给定关系之间的适当链接。基于此分析，得出与实体关系图一致的图，以包含给定关系之间的所有可能的一元和二元关系。确定所提到图形中每个链接的最小和最大基数，并标识和分类图形中的其他链接（如果有）。后一个信息对于优化与外键有关的信息是必需的。最后，该过程的最后步骤包括（在适用时）建议对原始概念设计进行改进，确定具有属性的关系，多对多和n元（n≥3）关系，并确定is-a链接。在系统不具有决定某个选择所需的语义知识的情况下，将用户对过程的参与降至最低。

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