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: b Structural aspect: s The data in the database is perceived by the user as tables b Integrity aspect: s Those tables satisfy certain integrity constraints b Manipulative aspect s The operators are available to the user for manipulating those tables
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A formal definition b Relational databases store data in the form of tables s The rows of a table are called as tuples s The columns of a table are known as attributes s Every attribute has a data type associated with it s Every attribute has a domain which provides the set of possible values s Tables are called as relations s The table names are called as relational variables (relvar)
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A Formal Definition
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Domains b A relation may be regarded as a set of tuples b A domain has a logical definitions: eg., “phone_number” are the set of 10 digit numbers b A domain defines posible values of an attribute, may have a data-type or a format defined for it b 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 b A relation schema is used to describe a relation b A relation schema R, denoted by R(A1,A2,. ..,An): s where R is a relation name and s A1,A2,. ..,An - a list of attributes b The degree of a relation is the number of attributes b Instance r of R : a specific “value” or population of R
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Characteristics b Ordering of tuples in a relation: s The tuples are not considered to be ordered, even though they appear to be in the tabular form b Ordering of attributes: s 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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This note was uploaded on 04/01/2012 for the course CSE,IT 101 taught by Professor Mirunaalini during the Spring '12 term at Indian Institute of Technology, Chennai.

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rdb_intro - Introduction to Relational Databases Informal...

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