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databaserelational-model

Meaningful tuple

I have a tabular representation of a relation called staff, I have been asked to complete a number of tasks like the degree and cardinality which is 5 and 3, but i have been asked why it is not meaningful to talk about the 2nd tuple in the relation and i have no idea why that would be the case.

*This is a practise exam, which came with no answers. Staff

Solution

  • A tuple is to a relation as a row is to a table.

    There is no notion of order in a relation (a relation is defined as an unordered set of tuples).

    In a table (as you have displayed), order is an artifact of display - there is no concept of order in the relational model (although one could add the concept as an attribute of a tuple/row).

    So there is no concept of the 1st, 2nd or 3rd tuple

    Similarly, in a SQL RDBMS, order of returned rows is not guaranteed except where an ORDER BY is specified.