The document discusses the key concepts of the relational data model including relations, attributes, tuples, domains, keys, and integrity constraints. A relation is a table with columns and rows where each cell contains a single value. Attributes are the columns and tuples are the rows. Relations must have a unique name and attributes within a relation must be distinct. Keys such as the primary key and foreign keys are used to uniquely identify and link tuples between relations. Integrity constraints like entity integrity and referential integrity enforce rules about relationships between tuples.

1. Relational Data Model
1

2. Chapter 2 - Objectives
 Terminology of relational model.
 How tables are used to represent data.
 Properties of database relations.
 How to identify PK, AK, and FKs.
 Meaning of entity integrity and
referential integrity.
2
© Pearson Education Limited 1995, 2005

3. Relational Model
Terminology
 A relation is a table with columns and
rows.
 Only applies to logical structure of the
database, not the physical structure.
 Attribute is a named column of a relation.
 Domain is the set of allowable values for
one or more attributes.
3
© Pearson Education Limited 1995, 2005

4. Relational Model
Terminology
 Tuple is a row of a relation.
 Degree is the number of attributes in a
relation.
 Cardinality is the number of tuples in a
relation.
 Relational Database is a collection of
normalized relations with distinct relation
names.
4
© Pearson Education Limited 1995, 2005

5. Instances of Branch and
Staff Relations
5
© Pearson Education Limited 1995, 2005

6. Examples of Attribute
Domains
6
© Pearson Education Limited 1995, 2005

7. Alternative Terminology for
Relational Model
7
© Pearson Education Limited 1995, 2005

8. Database Relations
 Relation schema
 Named relation defined by a set of attribute
and domain name pairs.
 Relational database schema
 Set of relation schemas, each with a
distinct name.
8
© Pearson Education Limited 1995, 2005

9. 9
Terminology
Name Price Category Manufacturer
gizmo $19.99 gadgets GizmoWorks
Power gizmo $29.99 gadgets GizmoWorks
SingleTouch $149.99 photography Canon
MultiTouch $203.99 household Hitachi
Tuples or rows or records
Attribute names
Table name or relation name
Products:

10. Schemas
Relational Schema:
 Relation name plus attribute names
 E.g. Product(Name, Price, Category,
Manufacturer)
 In practice we add the domain for each attribute
Database Schema
 Set of relational schemas
 E.g. Product(Name, Price, Category,
Manufacturer),
Company(Name, Address, Phone),
. . . . . . .
10

11. Example
11
Name Price Category Manufacturer
gizmo $19.99 gadgets GizmoWorks
Power gizmo $29.99 gadgets GizmoWorks
SingleTouch $149.99 photography Canon
MultiTouch $203.99 household Hitachi
Relational schema:Product(Name, Price, Category, Manufacturer)
Instance:

12. Properties of Relations
 Relation name is distinct from all other
relation names in relational schema.
 Each cell of relation contains exactly
one atomic (single) value.
 Each attribute has a distinct name.
 Values of an attribute are all from the
same domain.
12
© Pearson Education Limited 1995, 2005

13. Properties of Relations
 Each tuple is distinct; there are no
duplicate tuples.
 Order of attributes has no significance.
 Order of tuples has no significance,
theoretically.
13
© Pearson Education Limited 1995, 2005

14. Relational Keys
 Candidate Key
 A set of one or more attributes(minimal) that can
uniquely indentify a row/tuple in a given table.
 Primary Key
 Candidate key selected to identify row/tuple
uniquely within relation.
 Alternate Keys
 Candidate keys that are not selected to be primary
key.
 Foreign Key
 An attribute (or combination of attributes) in one
table whose values must match the primary key in
another table.
14
© Pearson Education Limited 1995, 2005

15. Choosing A Primary Key
 Give preference to numeric column(s)
 Give preference to single attribute
 Give preference to minimal composite attribute
15
© Pearson Education Limited 1995, 2005

16. Choosing Foreign Keys
 A Foreign key is a set of attribute(s) whose
values are required to match values of a column
in the same or another table.
16
© Pearson Education Limited 1995, 2005

17. Integrity Constraints
 Null
 Represents value for an attribute that is
currently unknown or not applicable for
tuple.
 Deals with incomplete or exceptional data.
 Represents the absence of a value and is
not the same as zero or spaces, which are
values.
17
© Pearson Education Limited 1995, 2005

18. Integrity Constraints
 Entity Integrity
 In a base relation, no attribute of a primary
key can be null.
 Referential Integrity
 If foreign key exists in a relation, either
foreign key value must match a candidate
key value of some tuple in its home
relation or foreign key value must be
totally null.
18
© Pearson Education Limited 1995, 2005

19. Integrity Constraints
 General Constraints
 Additional rules specified by users or
database administrators that define or
constrain some aspect of the enterprise.
19
© Pearson Education Limited 1995, 2005

20. Revision:
20
- Determine the Relational Data Model characterisics
(relation name, attribute, tuple, degree, cardinality,
primary key, foreign key and relation scheme) in the
given relation.

21. 21