0

How are two superclass entities that are connected to a mandatory 1-to-1 relationship converted to relational schemas? These two superclass entities are also abstract, meaning that they will not have a table, but their descendants will. Most probably the descendants tables' are somehow combined, but how?

Improve this question
4
  • mandatory 1-to-1 relationship? it cannot be realized in practice, because the data cannot be inserted into such structure (intermediate state 1-to-zero will occur). It must be 1-to-(0 or 1). I.e. One of entities must be "primary" and the another one must have UNIQUE constraint over the relational expression.
    – Akina
    Commented Dec 27, 2021 at 6:07
  • I've heard that these kinds of entities (that are connected with a mandatory 1-to-1 relationship) are combined into one relational schema during the conversion of the E-R diagram to relational schemas. Isn't that special case true? Does this notation exist just for better organization?
    – Some1
    Commented Dec 27, 2021 at 11:57
  • @Akina - It can be realized by setting one of the FKs to DEFERRABLE INITIALLY DEFERRED. With that setting, the FK isn't checked until COMMIT is called. But, that might be an Oracle thing. From (bad) experience, its an impractical physical design. In the end, I did not achieve the performance increase that I expected by splitting the data across two tables. In fact, I lost more time towards SW Development then I gained in DB search performance.
    – Michael Kutz
    Commented Dec 27, 2021 at 15:17
  • @MichaelKutz This is DBMS-dependent whereas OP asks in general.
    – Akina
    Commented Dec 27, 2021 at 16:08

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.