Download Data model

Relational Model
5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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Introduction
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The Relational Database Management System (RDBMS)
has become the dominant DBMS in use today.
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All data are logically structured withing relations (tables).
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Based on the relational data model proposedby Dr E.F .
Codd.
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Design methology will be based on the relational model
5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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What is a data model ?
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Data model : Integrated collection of concepts for
describing data (data requirements).
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A data model may comprise 3 componants :
5/22/2017
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A structural part ( rules on how database to be constructed)
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Manipulative part (Type of operations allowed on the data)
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Set of integrity rules ( to ensure data accuracy)
CPSC-4360-01, CPSC-5360-01, Lecture 4
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Terminilogy
In the relational model, we use relations ( tables ) to hold info
about the objects that we want to represent in the database.
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Relation
: Table with column and rows
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Attribute : named column of a relation
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Domain: set of allowable (possible)values for one or more attributes.
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Tuple: a record of a relation (row in the table)
Relational Database - collection of normalized relations with
distinct relation names.
5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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Examples of domain for attributtes
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CPSC-4360-01, CPSC-5360-01, Lecture 4
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Properties of Relations
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Table name is distinct from all other table names in the
database.
Each cell of table contains exactly one atomic (single) value.
Each column has a distinct name.
Values of a column are all from the same domain.
Each record is distinct (no duplicate record)
Order of columns has no significance.
Order of records has no significance, theoretically (affect
efficiency of accessing records )
© Pearson Education Limited, 2004
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Relational Keys
Each record in a table must be unique , so we need a mean
to provide this uniqueness.
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Superkey
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A column, or a set of columns (minimum number),
that
uniquely identifies a record within a table.
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Candidate Key “K”
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that record .
Irreducibility : No proper subset of K has the uniqueness
property
Uniqueness : value uniquely identify
© Pearson Education Limited, 2004
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“
Branch” table
“city”
cannot be selected as a candidate key for the Branch
table . Why?
What about “zipCode”?
5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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Composite key
Role
table represents the name of the character played by an
actor in videos.
5/22/2017
CPSC-4360-01, CPSC-5360-01, Lecture 4
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Relational Keys
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Primary Key
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Candidate key selected to identify records uniquely within
table.
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Alternate Keys
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Candidate keys that are not selected to be primary key.
Example : for Branch table , if “branchNo” is the primary
key then “zipCode” is the alternate key.
© Pearson Education Limited, 2004
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Relational Keys
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Foreign Key

Column, or set of columns, within one table that
matches candidate key of some (possibly same) table.
Note:
When a column appears in more than one table ,
its appearance usually represents a relationship
between records of the two tables
© Pearson Education Limited, 2004
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Relational Integrity

Every column has an associated domain (constraint
the value that a column can take).

There are 2 more important integrity rules that apply
to all instances of the database:
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Entity integrity
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Referential integrity
© Pearson Education Limited, 2004
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Relational Integrity
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Null
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Represents value for a column that is currently
unknown or not applicable for record.
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Deals with incomplete or exceptional data.
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Represents the absence of a value and is not
the same as zero or spaces, which are values.
© Pearson Education Limited, 2004
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Relational Integrity
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Entity Integrity
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In a base table, no column of a primary key can
be null.
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Referential Integrity
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If FK exists in a table, either FK value must
match a candidate key value of some record in
its home table or FK value must be wholly null.
© Pearson Education Limited, 2004
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Relational Integrity
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Business Rules
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Rules that define or constrain some aspect of the
organization.
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Example : a member can only rent a maximum of
10 videos at any one time.
© Pearson Education Limited, 2004
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Relational Languages
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Two main languages:
 SQL (Structured Query Language), standardized by
ISO.
 QBE (Query-by-Example), alternative graphical
“point-and-click” way of querying database.
© Pearson Education Limited, 2004
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Schema Diagram
Relational Database Keys
Table 2.3
Figure 2.4
An Illustration of Integrity Rules
An Example Table
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Students (sid: string, name: string, login: string, age:
integer, gpa: real)
sid
50000
53666
53688
53650
53831
53832
name
Dave
Jones
Smith
Smith
Madayan
Guldu
login
dave@cs
jones@cs
smith@ee
smith@math
madayan@music
guldu@music
age
19
18
18
19
11
12
gpa
3.3
3.4
3.2
3.8
1.8
2.0
Another example: Courses
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Courses (cid, instructor, quarter, dept)
cid
instructor
quarter
dept
Carnatic101
Jane
Fall 06
Music
Reggae203
Bob
Summer 06 Music
Topology101 Mary
Spring 06
Math
History105
Fall 06
History
Alice
Keys
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Primary key – minimal subset of fields that is
unique identifier for a tuple
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sid is primary key for Students
cid is primary key for Courses
Foreign key –connections between tables
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Courses (cid, instructor, quarter, dept)
Students (sid, name, login, age, gpa)
How do we express which students take each
course?