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POHow to Implement Referential Integrity in Subtypes
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I have the following tables in a relational database: <pre><code>[Sensor] LocationId [PK / FK -> Location] SensorNo [PK] [AnalogSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] UpperLimit LowerLimit [SwitchSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] OnTimeLimit [Reading] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] ReadingDtm [PK] [ReadingSwitch] LocationId [PK/FK -> Reading] SensorNo [PK/FK -> Reading] ReadingDtm [PK/FK -> Reading] Switch [ReadingValue] LocationId [PK/FK -> Reading] SensorNo [PK/FK -> Reading] ReadingDtm [PK/FK -> Reading] Value [Alert] LocationId [PK/FK -> Reading] SensorNo [PK/FK -> Reading] ReadingDtm [PK/FK -> Reading] </code></pre> Basically, ReadingSwitch and ReadingValue are subtypes of Reading and SwitchSensor and AnalogSensor are subtypes of Sensor. A reading can either be a SwitchReading or ValueReading value - it cannot be both, and a Sensor can either be an AnalogSensor or a SwitchSensor. The only way I've come across to do this so far is <a href="http://web.archive.org/web/20100309034643/http://consultingblogs.emc.com/davidportas/archive/2007/01/08/Distributed-Keys-and-Disjoint-Subtypes.aspx" rel="nofollow">here</a>. There surely must be a nicer way to do this sort of thing. The only other way I can think of is to not have sub types but completely expand everything: <pre><code>[SwitchSensor] LocationId [PK/FK -> Location] SensorNo [PK] [AnalogSensor] LocationId [PK/FK -> Location] SensorNo [PK] [SwitchReading] LocationId [PK/FK -> SwitchSensor] SensorNo [PK/FK -> SwitchSensor] ReadingDtm Switch [AnalogReading] LocationId [PK/FK -> AnalogSensor] SensorNo [PK/FK -> AnalogSensor] ReadingDtm Value [AnalogReadingAlert] LocationId [PK/FK -> AnalogReading] SensorNo [PK/FK -> AnalogReading] ReadingDtm [PK/FK -> AnalogReading] [SwitchReadingAlert] LocationId [PK/FK -> SwitchReading] SensorNo [PK/FK -> SwitchReading] ReadingDtm [PK/FK -> SwitchReading] </code></pre> Which might not be so bad but I also have tables that reference the Alert table, so they too would have to be duplicated: <pre><code>[AnalogReadingAlertAcknowledgement] ... [AnalogReadingAlertAction] ... [SwitchReadingAlartAcknowledgement] ... [SwitchReadingAlartAction] </code></pre> etc. Does this problem make any sense to anyone??
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<sql><database><relational-database><foreign-key-relationship>
Title
How to Implement Referential Integrity in Subtypes
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