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Relational Model & Algebra
CPS 116
Introduction to Database Systems
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Announcements
Please read news: duke.cs.cps116
Please sign up for DB2 accounts and indicate your
availability to attend discussion sessions (sign-up sheet is
circulating)
Lectures slides on Web
“Notes” version available in hardcopy and online an hour before
lecture
Complete version available online after the lecture
Homework #1 will be assigned next Tuesday
Office hours: see course Web page
Book update: Prentice-Hall sent something out yesterday
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Relational data model
A database is a collection of relations (or tables)
Each relation has a list of attributes (or columns)
Set-valued attributes not allowed
Each attribute has a domain (or type)
Each relation contains a set of tuples (or rows)
Duplicate tuples are not allowed
Simplicity is a virtue!
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Example
Student Course
Enroll
Ordering of rows doesn’t matter
(even though the output is
always in some order)
SID name age GPA
142 Bart 10 2.3
123 Milhouse 10 3.1
857 Lisa 8 4.3
456 Ralph 8 2.3
... ... ... ...
CID title
CPS116 Intro. to Database Systems
CPS130 Analysis of Algorithms
CPS114 Computer Networks
... ...
SID CID
142 CPS116
142 CPS114
123 CPS116
857 CPS116
857 CPS130
456 CPS114
... ...
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Schema versus instance
Schema (metadata)
Specification of how data is to be structured logically
Defined at set-up
Rarely changes
Instance
Content
Changes rapidly, but always conforms to the schema
Compare to type and objects of type in a
programming language
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Example
Schema
Student (SID integer, name string, age integer, GPA float)
Course (CID string, title string)
Enroll (SID integer, CID integer)
Instance
{ h142, Bart, 10, 2.3i, h123, Milhouse, 10, 3.1i, ...}
{ hCPS116, Intro. to Database Systemsi, ...}
{ h142, CPS116i, h142, CPS114i, ...}
