Chapter 4 The Relational Model .pdf - ISYS 464 MANAGING ENTERPRISE DATA Chapter 4 The Relational Model Agenda \u27a2Relational Model Definition

Chapter 4 The Relational Model .pdf - ISYS 464 MANAGING...

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ISYS 464 MANAGING ENTERPRISE DATA Chapter 4 : The Relational Model
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Agenda Relational Model Definition Integrity Constraints Transforming EER Diagrams into Relations Entities Binary Relationship Associative Entities Other Relationships Normalization Denormalization and Partitioning Data
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E-R model example :
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Relational model example
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Relation A relation is a named, two - dimensional table of data. A table consists of rows (records) and columns (attribute or field). Requirements for a table to qualify as a relation : It must have a unique name . Every attribute value must be atomic (not multivalued, not composite). Every row must be unique (can’t have two rows with exactly the same values for all their fields). Attributes (columns) in tables must have unique names . The order of the columns must be irrelevant. The order of the rows must be irrelevant.
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Correspondence with E - R Model Relations (tables) correspond to entity types and to many - to - many relationship types. Rows correspond to entity instances and to many - to - many relationship instances. Columns correspond to attributes. NOTE : The word relation (in relational database) is NOT the same as the word relationship (in E - R model).
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Key Fields Keys are special fields that serve two main purposes: Primary keys are unique identifiers of the relation. Examples include employee numbers, social security numbers, etc. This guarantees that all rows are unique. Foreign keys are identifiers that enable a dependent relation (on the many side of a relationship) to refer to its parent relation (on the one side of the relationship). Keys can be simple (a single field) or composite (more than one field).
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