rdb_intro - Introduction to Relational Databases Informal...

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Introduction to Relational Databases
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Informal look to Relational Databases The relational model is having the three aspects: box3 Structural aspect: square6 The data in the database is perceived by the user as tables box3 Integrity aspect: square6 Those tables satisfy certain integrity constraints box3 Manipulative aspect square6 The operators are available to the user for manipulating those tables
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A formal definition box3 Relational databases store data in the form of tables square6 The rows of a table are called as tuples square6 The columns of a table are known as attributes square6 Every attribute has a data type associated with it square6 Every attribute has a domain which provides the set of possible values square6 Tables are called as relations square6 The table names are called as relational variables (relvar)
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A Formal Definition
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Domains box3 A relation may be regarded as a set of tuples box3 A domain has a logical definitions: eg., “phone_number” are the set of 10 digit numbers box3 A domain defines posible values of an attribute, may have a data-type or a format defined for it box3 An attribute is the name of a role played by some domain. Eg.,domain Date may be used to define attributes “Invoice-date” and “Payment-date”
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Relation schema box3 A relation schema is used to describe a relation box3 A relation schema R, denoted by R(A1,A2,...,An): square6 where R is a relation name and square6 A1,A2,...,An - a list of attributes box3 The degree of a relation is the number of attributes box3 Instance r of R : a specific “value” or population of R
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Characteristics box3 Ordering of tuples in a relation: square6 The tuples are not considered to be ordered, even though they appear to be in the tabular form box3 Ordering of attributes: square6 We will consider the attributes in R(A1,A2,...,An) and the values in t = <v1,v2,...,vn> to be ordered.
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