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Transcript
Thomas Connolly
and Carolyn Begg’s
Database Systems:
A Practical Approach to Design,
Implementation, and Management
Chapter 4 Part One:
Relational Terminology
Of course, we are still using Kroenke’s slide format!
1-1
Today’s Objectives
• To understand the terminology of the
relational model.
• Properties of database relations
• The meaning of entity integrity and
referential integrity
1-2
The Relational Database Model
• The dominant database model is the
relational database model – all current
major DBMS products are based on it
• Created by IBM engineer E. F. Codd in
1970
• It was based on mathematics called
relational algebra
DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition
© 2006 Pearson Prentice Hall
1-3
The Relational Model
• “The Relational Database Management
System(RDBMS) has become the dominant
data-processing software in use today, with
estimated sales of between US$15 billion and
US$20 billion per year,…, and growing at a rate
of possibly 25% per year.” Connolly, Begg. P. 70
• A relation is viewed as a two dimensional table
of data where columns are the attributes of the
data and rows, or tuples, contain records of the
user data.
• Each row contains one piece of data per column.
1-4
Database Relations
• Relation schema: A named relation
defined by a set of attribute and domain
pairs. [p.76]
• Relational database schema: A set of
relation schemas, each with a distinct
name. [p. 76]
1-5
Properties of Relations
• The relation has a name that is distinct from all
other relation names in the relation schema
• Each cell of the relation contains exactly one
single value
• Each attribute has a distinct name
• The values of an attribute are all from the same
domain
• Each tuple is distinct
• The order of attributes has no significance
• The order of tuples has no significance
• [p.77]
1-6
Relational Keys
• Superkey: An attribute, or set of attributes, that
uniquely identifies a tuple within a relation.
• Candidate key: A superkey such that no proper
subset is a superkey within the relation.
• Primary key: The candidate key that is selected
to identify tuples uniquely within the relation.
• Foreign key: An attribute, or set of attributes,
within one relation that matches the candidate
key of some (possibly the same) relation.
• [p.80]
1-7
Relational Integrity
• Domain constraints form restrictions on the set
of values allowed for the attributes of relations.
• Null: Represents a value for an attribute that is
currently unknown or is not applicable for this
tuple.
• Entity Integrity: No attribute of the primary key
can be null.
• Referential Integrity: If a foreign key exists in a
relation, either the foreign key value must match
a candidate key value of some tuple in its home
relation or the foreign key value must be wholly
null.
1-8
Thomas Connolly
and Carolyn Begg’s
Database Systems:
A Practical Approach to Design,
Implementation, and Management
End of Presentation
Of course, we are still using Kroenke’s slide format!
1-9