Relational Model Introduction - E-Courses
Relational Model Introduction - E-Courses
Relational Model Introduction - E-Courses
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Keys for a Relation (1/2)<br />
• Key: A set of attributes K, whose values uniquely identify a<br />
tuple in any instance. And none of the proper subsets<br />
of K has this property<br />
Example: {rollNumber} is a key for student relation.<br />
{rollNumber, name} – values can uniquely identify a tuple<br />
• but the set is not minimal<br />
• not a Key<br />
• A key can not be determined from any particular instance data<br />
it is an intrinsic property of a scheme<br />
it can only be determined from the meaning of attributes<br />
Prof P Sreenivasa Kumar<br />
Department of CS&E, IITM<br />
4
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