The+Relational+Model

The+Relational+Model - The Relational Model Douglas Havelka...

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Unformatted text preview: The Relational Model Douglas Havelka Miami University Mathematical Basis Predicate logic Set theory Three components: Logical data structure = relations Integrity rules Operations Logical v physical view Tables Relation Group of related instances, I.e. a set 2D, rows and columns Tuple represents one element of the set, I.e. an instance Column represents attributes Each must have a unique name Each row/column intersection represents a single value All values in a column have same format Each column has a range of values, the attribute domain Order of the rows and columns is not important Every table has an attribute (or combination of attributes) that uniquely identifies each row The primary key Database Systems, 9th Edition 8 Table Characteristics Some Attribute formats: Numeric Character or text or string Date Logical or boolean Keys Used to identify data and establish relationships Key one or more attribute values that determine other attribute values Functional Dependence Determination the values of certain attributes depend on the value of others A -> B, C, D If you know the value of A, then you can determine the values of B, C, and D Can occur more than once in a table Composite key a key that is composed of more than one attribute A multi-attribute key The attributes that make up a composite key are called key attributes Full functional dependence Attributes are dependent on a composite key, but none of its key attributes Superkey Any key that will uniquely identify all instances Candidate key A superkey without any unnecessary key attributes, a minimal superkey Primary key...
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This note was uploaded on 04/01/2012 for the course MIS 245 taught by Professor Havelka during the Spring '12 term at Miami University.

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The+Relational+Model - The Relational Model Douglas Havelka...

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