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Equivalence of Databases (Notion of)?

  1. May 31, 2015 #1

    WWGD

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    Hi All,
    Say we have two databases D1, D2, with the same number of entities and with equal functionality diagrams
    (i.e., the functional dependence graphs are graph-isomorphic). Is there a notion in database under which D1, D2 are considered to be "the same" database , or some term equivalent to the same, as in the term "isomorphic" in Mathematics?
     
  2. jcsd
  3. May 31, 2015 #2

    jim mcnamara

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    Do you mean the "same" schemas, just a different data set? AFAIK there is no really analogous term in relational db theory to isomorphic. And if such a thing existed it would not convey very much meaning. Data in a db changes its functionality due to different requirements for data reporting, for example. We have differing indexes and code hints (for SQL queries in db's with identical schema owners), but because of use patterns (indexes, etc.) are actually different. If this were not true DBA's would be out of work. OR have a lot less to do at any rate.
     
  4. Jun 1, 2015 #3

    WWGD

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    Thanks, DH. But isomorphisms most often refer to the preservation of part of the structure, and not all of its aspects, i.e., we can have the Reals be isomorphic to some other set as a group, field, as an ordered field, etc. So I guess the isomorphism here would (it it was defined) preserve the schema, though not necessarily the contents or the semantic aspect. And , is there a way of comparing the semantics/content of different dbs?
     
  5. Jun 2, 2015 #4

    Mark44

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    Um, that was jim mcnamara who replied, not D H.
     
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