Lab Assignment 1

Lab Assignment 1 - Lab Assignment 1 Dated May 4 2010 Name...

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Lab Assignment # 1 Dated: May 4, 2010 Name: Waqas Javed Exercise 3.1 (a) Relation In the relational model, all data is logically structured within relations. Relation is a table with columns and rows. It used to hold information about objects to be represented in the database. (b) Attribute Attribute is the named column of a relation. It can appear in any order and the relation will still be the same relation and convey the same meaning. (c) Domain A domain is the set of allowable values for one or more attributes. It is an extremely powerful feature of the relation model. Domain may be distinct for each attribute. It allows a user to define in central place the meaning and source of values that attribute can hold. (d) Tuple A tuple is a row of a relation. Each tuple contains one value per attribute. Like attributes, tuple can appear in any order and the relation will still be the same relation and convey the same meaning. (e) Intension and Extension Data is logically structured within relations in relational model. The structure of the relation, together with a specification of the domains and other restrictions on its values are called intensions. Number of columns in a table is an example of intensions. Intensions are fixed unless the meaning of the relation is changed. Though, the tuple changes over time and its called extensions. (f) Degree and cardinality The degree of a relation is the number of attributes it contains. Degree is a property of the intension of the relation. The cardinality of a relation is the number of tuples it contains. Cardinality changes as tuples are added or removed in relation. Cardinality is property of the extension of the relation.
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Exercise 3.4 Following are the properties of the relations. 1. Each cell of the relation contains exactly one atomic value. 2. The relation has a name. It is distinct from all other relation names of the relational schema. 3. Each attribute of a relation has a distinct name. 4. The values of an attribute of a relation are all from the same domain. 5.
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This note was uploaded on 05/13/2010 for the course COMPRO CS401 taught by Professor Just during the Spring '10 term at Maharishi.

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Lab Assignment 1 - Lab Assignment 1 Dated May 4 2010 Name...

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