Relational data integrity
Relational data integrity
Lecture 8
1
Relational data integrity
Outline
 integrity constraints and data definition
 candidate keys
 foreign keys
 nulls
 domains
 conditional expressions
 normal forms
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Relational data integrity
Constraints
 in real life systems constraints exist between
data values
• it would be useful to communicate these constraints to
the database system
 data is associated with a meaning
• stating some constraints on data  describing a part of
the meaning
 90% should be spent on integrity constraints
definition
3
Relational data integrity
Examples of possible inaccuracies
Persons
ID
Name
1
M. Jackson
3
P$%ffY780&&&
3
F. Mercury
Departments
Department
MM01
PPP
DoB
22/12/1960
01/04/2099
07/07/1957
Name
Manufacturing management
Personnel
Income
34000
28000
-50000
Department
MM01
MM01
Dev10
?
No_of_employees
3
4
?
how would you express, in NL, integrity constraints
that would avoid the above situations?
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Relational data integrity
Types of integrity constraints
 integrity constraint
 application specific integrity constraints
 examples
 mechanisms
• domains
• conditional expressions
• normal forms
 generic (inherent to the relational model resulting from definitions)
• entity integrity : primary key
• referential integrity : foreign key
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Relational data integrity
Data definition
 integrity constraints definition in a relational
language should include




primary key definition
candidate keys definition
foreign key definition - including foreign key rules
conditional expressions
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Relational data integrity
Example - SQL data definition (in brief)
CREATE TABLE <relation name> (
@<attribute definition><conditional expression>,
<primary key definition>,
@<candidate key definition>,
@<foreign key definition>,
@<conditional expressions>
);
<primary key definition> ::=
PRIMARY KEY ( <set of attributes> )
<candidate key definition > ::= CANDIDATE KEY ( <set of attributes> )
<foreign key definition> ::=
FOREIGN KEY ( <set of attributes> )
REFERENCES <relation name>
ON DELETE <option>
ON UPDATE <option>
CREATE ASSERTION <name> CHECK <conditional expression>
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Relational data integrity
Candidate key - example
Registration-no
Name
one candidate key
DOB
Tel-no
Course
…
other candidate keys
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Relational data integrity
Candidate key
 candidate key
 uniqueness property
 irreducibility property
 entity integrity constraint
 simple/composite
 primary/alternate
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Relational data integrity
Foreign key - example
Registrations
Students
Address
London
London
York
Leeds
Bath
SName
M. Jagger
S. Smiths
S. Smiths
S. Bruce
J. Kelly
Course
CIS
CIS
MCS
MAS
MAS
SName
M. Jagger
M. Jagger
M. Jagger
S. Smiths
S. Smiths
S. Smiths
S. Smiths
S. Smiths
J. Kelly
J. Kelly
Course
CIS
CIS
CIS
CIS
CIS
CIS
MCS
MCS
MAS
MAS
Module
Languages
Databases
Compilers
Languages
Databases
AI
Languages
Calculus
Calculus
Statistics
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Relational data integrity
Foreign key
 foreign key (FK)
  corresponding candidate key (CK) in another relation
  FK  CK such that FK = CK (reverse not required)
 target/referenced relation/tuple |
referring relation/tuple
 referential integrity constraint
 foreign keys and PostgreSQL
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Relational data integrity
Referential diagram
Students
Tutors
Registrations
Teaching
Modules
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Relational data integrity
Foreign key rules - motivation
Type
curr
s-sav
l-sav
…
Name
MinDep
Interest
current
short savings
long savings
…
100
1000
10000
…
Name
No
M. Smith
M. Smith
M. Jagger
S. Hunt
…
0099455321
1011334522
0099677432
1011377856
…
2.4
3.3
4.5
…
Type
curr
s-sav
curr
s-sav
…
Balance
-342.22
1500
235.99
2300
…
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Relational data integrity
What happens if ...
 short saving accounts are not offered by the
bank anymore?
 the “code” and name for small saving
accounts is to be changed to ‘i-sav’ and
‘instant saving’ respectively?
 the interest for s-sav is to be decreased by
0.3%?
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Relational data integrity
Foreign key rules
 the modifications are performed in the
REFERRED relation
 rules
•
•
•
•
ON DELETE RESTRICT
ON DELETE CASCADE
ON UPDATE RESTRICT
ON UPDATE CASCADE
 split into four groups: think of one example for
each situation; don’t use the study guide
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Relational data integrity
Examples
 on delete restrict
• students and books
 on delete cascade
• employees and children
 on update restrict
• students and modules
 on update cascade
• employees and departments
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Relational data integrity
Nulls
Name
A. Johnson
S. Bruce
P. Harris
DOB
04/66
02/72
10/73
Sex
M
F
NULL
Course
CIS
NULL
MAS
Year1
68
NULL
0
Year2
72
NULL
48
Year3
NULL
NULL
NULL
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Relational data integrity
Nulls
 representing missing/unavailable information
 primary key and nulls
 foreign key and nulls
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Relational data integrity
Domains
 expressing integrity constraints on scalar
values
• constraints on permissible scalar values
• constraints on the applicability of scalar operators
 SQL
• does not support domains
• offers other mechanisms
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Relational data integrity
Domains - example of integrity constraints
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Relational data integrity
Conditional expressions
 will be studied with SQL
 pointer forward:
 the university’s database:
“a student has two choose two options (1/2cu
courses) in the final year; if the students chooses
an extra optional course than the final year project
will count as only 1/2cu”
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Relational data integrity
FDs, MDs, and JDs
 particular constraints
 functional dependencies
 multiple dependencies
 join dependencies
 expressed by means of normal forms
 extensively studied in the following lectures
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Relational data integrity
Normal forms - example
redundant data
Employees
ID
D1
D2
D3
D4
D5
D6
F1
Name
M. Rick
F. Boyle
P. Wale
M. Grin
F. Weller
S. Strauss
P. Johnson
Department
Development
Development
Development
Development
Development
Development
Finance
YearsInService
5
5
5
6
8
8
9
Qualification
programmer
programmer
programmer
analyst
analyst
analyst
accountant
Salary
28000
28000
28000
32000
41000
41000
28000
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Relational data integrity
Integrity constraints - further considerations
 state and transition integrity constraints
• example
 when and how are the integrity constraints applied
 depends on the type
• ‘normal forms’ and ‘domains’ - always
• entity and referential - after each transaction
• conditional expressions
– default : after each transaction
– other possibilities?
• correct database = the logical AND of the set of integrity
constraints is satisfied after each transaction
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Relational data integrity
Summary
 the relational data model
• data objects
• operators
• integrity constraints
 SQL implements the relational model
• the subject of the next lectures
 you know what a relational model is, but do
not know yet how to design one
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