Posted on 2005-04-19
Last Modified: 2012-05-05
Can anyone concisely describe what it is?
Question by:j_byron
    LVL 6

    Accepted Solution

    Chris Date (The CJ Date who wrote my university relational theory textbooks perhaps) describes it here:



    Author Comment

    Already read that and don't really understand it...
    LVL 9

    Assisted Solution

    That link is actually the most concise description I have seen.

    Is it the definitions?
    A relvar is a relational variable that contains a set of attributes, and a domain.  To define this in terms of what you see in DBMS products, the relvar is most closely associated to a table, an attribute to a column, and a domain to the rules that maintain the referential integrity of the table.  The domain definition could be as simple as a list of all possible values (Male, Female) for one of the attributes (a FK relationship), uniqueness of the key, or have more complcated rules related to other tables (the count example he gives, or even a cross-relation formula).

    DKNF is a test you can apply to a specific scenario.  If you can implement all of the domain rules in the DBMS such that they are enforced automatically, then the relation is said to be in DKNF.

    Author Comment

    I am splitting the points as rherguth's explanation helped me understand chedgey's link.

    That ok?

    LVL 9

    Expert Comment

    Fine by me.

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