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Topic: Candidate key

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	Candidate key -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-21)
		The importance of candidate keys is that they tell us how we can identify individual tuples in instances of a relation.
		Note that we have to consider all instances of a relation to determine whether a certain set of attributes is a candidate key.
		In order to correctly determine the candidate keys it is important to determine all superkeys, which is especially difficult if the relation represent a set of relationships rather than a set of entities.
	www.absoluteastronomy.com /encyclopedia/c/ca/candidate_key.htm (787 words)

	Primary key - Wikipedia, the free encyclopedia
		In the relational model of data, a primary key is a candidate key chosen as the main method of uniquely identifying a tuple in a relation.
		A surrogate key may be used as the primary key to avoid giving one candidate key artificial primacy over the others.
		The primary key should be immutable, meaning that its value should not be changed during the course of normal operations of the database.
	en.wikipedia.org /wiki/Primary_key (347 words)

	Information Resource Management Glossary
		Data Architecture theories such as the “normalization” are applied to transform the conceptual data model into the logical data model that moves the data modelling further towards the ultimate prescription for the data architecture to be implemented.
		As long as the resulting physical data model includes the necessary foreign key columns and joins, the inclusion of foreign-keys in the logical data model is a matter of convenience.
		The mapping of conceptual or logical database design data groupings into physical database areas, files, records, elements, fields, and keys while adhering to the physical constraints of the hardware, DBMS software, and communications network to provide physical data integrity while meeting the performance and security constraints of the services to be performed against the database.
	www.cio.gov.bc.ca /other/daf/IRM_Glossary.htm (5683 words)

	ipedia.com: Database normalization Article (Site not responding. Last check: 2007-10-21)
		Second Normal Form (or 2NF) requires that there are no non-trivial functional dependencies of a non-key attribute on a part of a candidate key.
		At this stage, all attributes are dependent on a key, a whole key and nothing but a key (excluding trivial dependencies, like A->A).
		- A superkey K holds as a candidate key for a relation universe U over H if it holds as a superkey for U and there is no proper subset of K that also holds as a superkey for U.
	www.ipedia.com /database_normalization.html (1609 words)

	information.ca - Surrogate key (Site not responding. Last check: 2007-10-21)
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	www.information.ca /Surrogate-key/reference/fullview/wikipedia/472950 (255 words)

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