The Global conceptual Schema in a distributed database contains information…
2016
The Global conceptual Schema in a distributed database contains information about global relations. The condition that all the data of the global relation must be mapped into the fragments, that is, it must not happen that a data item which belongs to a global relation does not belong to any fragment, is called :
- A.
Disjointness condition
- B.
Completeness condition
- C.
Reconstruction condition
- D.
Aggregation condition
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Correct answer: B
Answer: Completeness condition
Definition: The completeness condition requires that every data item (every tuple) of the global relation appears in at least one fragment. No data item belonging to the global relation should be left unmapped to fragments.
Reconstruction condition: Ensures the global relation can be obtained from the fragments (for example, by union for horizontal fragmentation or by join for vertical fragmentation). Completeness is a necessary part of successful reconstruction, but reconstruction focuses on recoverability.
Disjointness condition: Requires fragments not to overlap in their data items (no tuple appears in more than one fragment). This concerns overlap, not whether all data are mapped.
Aggregation condition: Not a standard name for the mapping requirement described; typically refers to combining or summarizing data rather than the coverage of fragments.
Summary: The completeness condition is the precise term for the requirement that all data items of a global relation be included in the set of fragments.