Formal Definitions in tuple relational calculas

Posted By on October 4, 2014


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Example Queries in tuple relational calculas
Safety of Expressions in tuple realtional calculas

Formal Definitions

  1. A tuple relational calculus expression is of the form

    where is a formula.

    Several tuple variables may appear in a formula.

  2. A tuple variable is said to be a free variable unless it is quantified by a or a . Then it is said to be a bound variable.
  3. A formula is built of atoms. An atom is one of the following forms:
    • , where is a tuple variable, and r is a relation ( is not allowed).
    • , where and are tuple variables, and and are attributes, and is a comparison operator ().
    • , where is a constant in the domain of attribute .
  4. Formulae are built up from atoms using the following rules:
    • An atom is a formula.
    • If is a formula, then so are and .
    • If and are formulae, then so are , and .
    • If is a formula containing a free tuple variable , then

      are formulae also.

  5. Note some equivalences:
Example Queries in tuple relational calculas
Safety of Expressions in tuple realtional calculas

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Posted by Akash Kurup

Founder and C.E.O, World4Engineers Educationist and Entrepreneur by passion. Orator and blogger by hobby

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