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Chapter 5 The Relational Data Model

Relational Model Concepts . The Relational Model of Data is based on the concept of a RelationA Relation is a two-dimensional tableThe columns of the table represent attributesThe rows of the table represent entities. Relational Model Concepts. A relation schema is the name and the list of attrib

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Chapter 5 The Relational Data Model

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    1. Chapter 5 The Relational Data Model By Yue Lu CS157B Spring 2008 Instructor: Dr.Lee

    2. Relational Model Concepts The Relational Model of Data is based on the concept of a Relation A Relation is a two-dimensional table The columns of the table represent attributes The rows of the table represent entities

    3. Relational Model Concepts A relation schema is the name and the list of attributes of a relation Grade (studentId, assignmentId, points, dateSubmitted) A tuple is a row of a table, one value for each attribute (101, 102, 92, 2/28/08)

    4. Model Concepts Domain D is a set of atomic values Atomic means that each value is indivisible Attribute A is the name of a role played by some domain Relation schema R is the specification of a relation Given by a name and list of attributes Degree of a relation is the number of attributes Relation (instance) r(R) of a relation schema A set of n-tuples, n is degree of relation schema

    5. Characteristics of Relational Model Relation is a set of tuples No ordering of tuples No duplicate tuples no two rows have all the same values Each attribute value is atomic So no multiple-valued or composite attributes called first normal form Each relation is a set of assertions Each represents a fact Some facts are about relationships

    6. Representing E-R Model as Relations Entity class ? Relation schema Entity ? row of table set of all entities of class ? table Attribute ? column definition (attribute) attribute value ? table element Relationship type ? relation schema attribute(s) of relation schema

    7. Example of Relation Schema and Table Figure 4.2 P75 Customer(accountID,lastName,firstName, street, city, state, zipcode, balance)

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