Chapter 3 Final

# Chapter 3 Final - King Saud University College of Computer...

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17/01/1438 >#< 1 Introduction to Database Systems Fall 2016 Dr. Ahmed Emam [email protected] [email protected] King Saud University College of Computer and Information Sciences Department of Information Systems THE RELATIONAL DATA MODEL AND RELATIONAL DATABASE CONSTRAINTS

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17/01/1438 >#< 2 Chapter 3 Outline The Relational Data Model and Relational Database Constraints Relational Model Constraints and Relational Database Schemas Update Operations, Transactions, and Dealing with Constraint Violations Relational Model Concepts The relational Model of Data is based on the concept of a Relation The strength of the relational approach to data management comes from the formal foundation provided by the theory of relations We review the essentials of the formal relational model in this chapter In practice , there is a standard model based on SQL this is described in Chapters 8 and 9 Note: There are several important differences between the formal model and the practical model, as we shall see
17/01/1438 >#< 3 Relational Model Concepts 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 in the following paper: " A Relational Model for Large Shared Data Banks," Communications of the ACM, June 1970 The above paper caused a major revolution in the field of database management and earned Dr. Codd the coveted ACM Turing Award Informal Definitions Informally, a relation looks like a table of values. A relation typically contains a set of rows. The data elements in each row represent certain facts that correspond to a real-world entity or relationship In the formal model, rows are called tuples Each column has a column header that gives an indication of the meaning of the data items in that column In the formal model, the column header is called an attribute name (or just attribute)

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17/01/1438 >#< 4 Example of a Relation 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
17/01/1438 >#< 5 Schema Definitions The Schema (or description) of a Relation: Denoted by R(A1, A2, ..... An) R is the name of the relation The attributes of the relation are A1, A2, ..., An Example: CUSTOMER (Cust-id, Cust-name, Address, Phone#) CUSTOMER is the relation name Defined over the four attributes: Cust-id, Cust-name, Address, Phone# Each attribute has a domain or a set of valid values.

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