Relational Database Model PDF

Chapter 3 The Relational Data Model and Relational Database Constraints Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley The Relational Data Model and Relational Database Constraints  A Relation is a mathematical concept based on the ideas of sets...

Chapter 3 The Relational Data Model and Relational Database Constraints Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley The Relational Data Model and Relational Database Constraints  A Relation is a mathematical concept based on the ideas of sets  The model was first proposed by Dr. E.F. Codd of IBM Research in 1970  First commercial implementations available in early 1980s  Has been implemented in a large number of commercial system Copyright © 2011 Ramez Elmasri and Shamkant Navathe  Relational Model Concepts  Represents data as a collection of relations  Informally, a relation looks like a table of values  Table of values  Row Represents a collection of related data values Fact that typically corresponds to a real-world entity or relationship  In the formal model, rows are called tuples  Table name and column names Interpret the meaning of the values in each row attribute Copyright © 2011 Ramez Elmasri and Shamkant Navathe  Relational Model Concepts (cont’d.) Copyright © 2011 Ramez Elmasri and Shamkant Navathe Domains, Attributes, Tuples, and Relations  Domain D  Set of atomic values  Atomic  Each value indivisible  Specifying a domain  Data type specified for each domain Copyright © 2011 Ramez Elmasri and Shamkant Navathe  Informal Definitions  Key of a Relation:  Each row has a value of a data item (or set of items) that uniquely identifies that row in the table Called the key  In the STUDENT table, SSN is the key  Sometimes row-ids or sequential numbers are assigned as keys to identify the rows in a table Called artificial key or surrogate key Slide 5- 6 Copyright © 2011 Ramez Elmasri and Shamkant Navathe Domains, Attributes, Tuples, and Relations (cont’d.)  Relation schema R  Denoted by R(A1, A2,...,An)  Made up of a relation name R and a list of attributes, A1, A2,..., An  Attribute Ai  Name of a role played by some domain D in the relation schema R  Degree (or arity) of a relation  Number of attributes n of its relation schema Copyright © 2011 Ramez Elmasri and Shamkant Navathe Domains, Attributes, Tuples, and Relations (cont’d.)  Relation (or relation state)  Set of n-tuples r = {t1, t2,..., tm}  Each n-tuple t Ordered list of n values t =