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Define Query by Example
QBE is a query language relies upon domain calculus and has two dimensional syntax. The queries are written in the horizontal and vertical dimensions of table. Queries are made by entering an instance of a possible answer in a skeleton table as displayed in the following diagram:
Conditions particular in a single row are ANDed and conditions illustrated in separate rows are ORed. The tuple operations are P., I ., etc., for PRINT, insert commands, resp. The variable names are illustrated by preceding their name with an underscore. QBE as well provides a "conditions" box to specify additional constraints that is why the conditions that cannot be added in a Skelton table can be entered in the conditions table. The aggregation operations such as max., min, sum. etc. are also provided by QBE.
A collection of a same kind of entities is known as an Entity Set or entity type. Example: For the COLLEGE database defines earlier objects of concern are Students, Faculty,
Define average latency time. The average latency time of the disk is one-half the time for a full rotation of the disk.
growing phase and shrinking phase are disjoint, why ?
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What are the two approaches to store relations in distributed database? a) Replication b) Fragmentation
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