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  1. #1
    Join Date
    Nov 2003

    Database: Mapping 1:1 relationship into relational schema

    Please refer to the attached image. Assuming the two entities, S and T are partially participating through the relationship 'relates'. Also the cardinality is 1:1. Also, assume that each entity is related to other entities, therefore we cannot merge them.
    My question is do I have to use each relation's primary key for the each others's foreign key (S will have FK referencing T and T will have FK referencing S)? Or I only must have FK in only one of the relations, and if so which one? Thank you in advance.
    Attached Thumbnails Attached Thumbnails Database Mapping 11 relational schema.jpg  

  2. #2
    Join Date
    Feb 2004
    In front of the computer
    In a truly 1:1 relationship, there is only one object. In other words, S and T are simply parts or subsets of the same (parent) thing. The A and X attributes literally are the same thing, one thing with two designations or names.

    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

  3. #3
    Join Date
    May 2016
    Hi rassuls

    For modeling correctly a db (See example on this dbforums post

    1. build a conceptual data model (CDM). The Logical data model is very simple then to generate. With tools, the LDM is automatically built as well as the SQL script for creating the DB
    2. Use dedicated tools which build CDM not only LDM like :
      1. Power*AMC (excellent but expensive)
      2. JMERISE, excellent freeware here

    And of course apply at least the 3 first Normal forms (NF).

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