3024-Chap10 - 10. RELATIONAL DATA MODELING Last chapter:...

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10. RELATIONAL DATA MODELING Last chapter: how to construct conceptual schema, as E- model (diagrams) R model (diagrams). Next step in building a database: translating conceptual chema into lational schema schema into relational schema . = relational data modeling Let’s examine relational modeling, again in the context of nna’s Books. Anna s Books. We’ll then develop relational schema for both Anna’s ooks and JA Machining 2010 John P. Shewchuk ISE 3024 Course Notes 10 – 1 Books and JA Machining.
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10.1 Introduction to the Relational Model Relational data model = description via set of two- imensional tables dimensional tables. ‘Table’ is a logical, rather than physical concept, here. • users model and manipulate data via tables. p • data not physically stored as tables in computer, however. Also keep in mind that relation and relationship are two ifferent things! 2010 John P. Shewchuk ISE 3024 Course Notes 10 – 2 different things!
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elational schema = articular instance of the relational Relational schema particular instance of the relational model. (i.e., for a given problem) Example: relational schema and partial relation for entity class Customer : Customer(customerId ,lastName,firstName,street, city,state,zip) customer Id last Name first Name street city state zip 3 Smith John 214 Church St. Blacksburg VA 24073 17 Davis Diane 185 Clay St. Blacksburg 24073 6 O’Keefe Patrick 35 Cambria St. Christiansburg 24061 2010 John P. Shewchuk ISE 3024 Course Notes 10 – 3 g
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ow does the table correspond to our E- model? How does the table correspond to our E R model? • column headings ata in col mns • data in columns • rows (records) Attributes in a relation schema must be atomic , i.e., alues which cannot be further decomposed and still values which cannot be further decomposed and still provide information. omposite and multivalued attributes must composite and multivalued attributes must somehow be translated into equivalent single-valued attributes. 2010 John P. Shewchuk ISE 3024 Course Notes 10 – 4
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he relation schema specifies The relation schema specifies • the name of the relation (table). • the name of each attribute. • at least one key for the relation. - value(s) for which key attribute(s) must be unique for each row (entity). - a relation for which this is true is said to exhibit ? Also not that the order of rows and columns in a table does not matter. ame attributes records regardless 2010 John P. Shewchuk ISE 3024 Course Notes 10 – 5 • same attributes, records regardless.
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10.2 Developing Relational Schema Specific rules are used for translating E-R diagrams into lational schema relational schema. The rules are applied in the following sequence: i) Entity classes ttributes odify relations to include attributes ii) Attributes iii) Relationships - modify relations to include attributes.
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This note was uploaded on 02/14/2010 for the course ISE 3024 taught by Professor Staff during the Spring '08 term at Virginia Tech.

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3024-Chap10 - 10. RELATIONAL DATA MODELING Last chapter:...

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