Distributed Database Question Bank with Answers 17

Distributed  and parallel database questions and answers for University exams

Question:

Is there any relationship between semi-join computation and derived horizontal fragmentation? Justify your answer.

Answer:

Yes. Derived horizontal fragmentation is defined on the member relation of a link according to the selection operation defined on its owner, i.e. produces a fragment of the member relation which contains only tuples which are guaranteed to join with tuples in the owner relation (and satisfy some selection condition).

In a semijoin, say R ⋉ S, the joining column of s (owner) is sent over to r (member) to produce the horizontal fragment of r that is guaranteed to join with s. As a result, it retains all the correct tuples resulted in the join and only attributes of R.

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