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Hi everyone,

I have a couple of questions regarding ER to Relational Schema Translation.

1. Do I treat a subclass entity as strong entity

2. Do I need to merge entities where most of the attributes are the same

Please advice.

Thank you

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Last Post by kay21
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I have a Superclass entity EMPLOYEE with Employee_SSN, Employee_Name, Designation, Salary as its attributes and two Subclass entities NURSE with Nurse_ID, Department as attributes and DOCTOR with Doc_ID, Specialty as its attributes.

Do I treat the NURSE and DOCTOR subclass entity as strong entity when mapping to relational schema?

1. You need to pass more information.
2. Yes.

Attachments Superclass_Subclass.jpg 53.87 KB
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I would, especially if you were going to have separate Department and Specialty entities translate to their own physical tables (for referential integrity's sake). If you don't plan to separate Specialty and Department as entities, then I wouldn't bother.

Just out of curiosity, where is there a reference to the symbol set you're using? It's not UML, IDEF, Martin, Chen, Gane/Sarson, DeMarco or any other one I've seen. Enquiring minds want to know... :-)

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No, there will not be a separate Department and Specialty entities. We were asked to use the 8 steps algorithm found in Fundamentals of Database Systems textbook to convert the EER to Relational Schema.

This link describes the 8 steps algorithm http://www.acs.uwinnipeg.ca/3902/Ch09.pdf

The diagram is just a part of the EER Diagram that I have created for a Hospital database assignment.

I would, especially if you were going to have separate Department and Specialty entities translate to their own physical tables (for referential integrity's sake). If you don't plan to separate Specialty and Department as entities, then I wouldn't bother.

Just out of curiosity, where is there a reference to the symbol set you're using? It's not UML, IDEF, Martin, Chen, Gane/Sarson, DeMarco or any other one I've seen. Enquiring minds want to know... :-)

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