CSE 132B Lecture Notes - Lecture 4: Candidate Key, Functional Dependency, Query Optimization
15 Jan 2019
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Document Summary
Many-to-one and one-to-many rses that are total on the many-side can be represented by adding an extra attribute to the many side, containing the pk of the one side. For 1-1 rses, either side can be chosen to act as the many side. If participation is partial on the many side, replacing a schema by an extra attribute in the schema corresponding to the many side could result in null values. Schema corresponding to a rs linking a wes to its identifying ses is redundant. Composite attr. are flattened out by creating a separate attribute for each component attr. A multivalued attributes m of an entity e is represented by a separate schema em. Em has attr. corresponding to the pk of e and an attr. corresponding to m. Ex: name has first, last names flatten out to create name_first and name_last. For a schema for each ll entity set, include pk of hl entity set and local attr.
