Information Technology Reference
In-Depth Information
• UniquenessofRecords:Allrows(records)ofarelationaredistinct.Thisimplies
that there must be a primary key for each record.
• RowOrdering:Theorderingofrowswithinarelationisimmaterial.
• ColumnOrdering:Thecolumnsofarelationareassigneddistinctnamesandthe
ordering of the columns is immaterial.
For example, the following represents a relational model for university enrollment,
where each table is a relation.
Relation Course
Course
Course-title
Location
CS101
Introduction to Computer Science
Lecture Theater 1
IS201
System Analysis
Lecture Theater 2
IS301
Decision Support System
Room P7818
Relation Prerequisite
*Course#
Prerequisite
Prereq-title
IS301
IS201
System Analysis
Relation Instructor
Inst-name
SS#
Inst-addr
A.B. Adams
415223614
White Plains
J.S. Fink
613557642
Brooklyn
A.M. Jones
452113641
Long Island
Relation Section
SS#
* Course
Section#
Lecture-hour
415223614
CS101
1
30
613557642
CS101
2
30
Relation Graduate Student
Student#
Degree-to-be
012888
M.Sc.
120008
Ph.D.
Search WWH ::




Custom Search