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POExpressing an is-a relationship in a relational database
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2008-09-24T21:52:01.897
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I was wondering if there is a clean way to represent an is-a relationship as illustrated by this example: This DB stores recording times for three types of programs: movies, game shows, drama. In an object oriented sense each of these is-a program. Each of these subclasses have different properties. Here are the tables (fk prefix indicates a foreign key): movie id name fkDirector gameShow id name fkHost fkContestant drama id name In OO terms the record table would in sense look like this: record id fkProgram startTime endTime The only way I can think of doing this without violating the normal forms is to have three record tables namely recordMovie, recordGameShow, and recordDrama. Is there a way to consolidate these tables into one without violating the principles of database normalization? Here are some non-working examples to illustrate the idea: program id fkMovie fkGameShow fkDrama This table violates the first normal form because it will contain nulls. For each row only one of the 3 entries will be non null. program id fkSpecific ← fkMovie OR fkGameShow OR fkDrama fkType ← would indicate what table to look into Here I will not be able to enforce referential integrity because the fkSpecific could potentially point to one of three tables. I'm just trying to save the overhead of having 3 tables here instead of one. Maybe this simply isn't applicable to an RDB.
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<database-design><schema><relational><oop>
Title
Expressing an is-a relationship in a relational database
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