The document provides an overview of relational model terminology, explaining key concepts such as entities, relations, attributes, and domains. It outlines the properties of relation schemas, relational keys (including super keys and candidate keys), and the significance of primary and foreign keys in relational databases. Additionally, examples are provided to illustrate how these concepts apply to practical database scenarios.

1. UNIT 2
RELATIONAL AND E-R MODELS[2.0-
2.2]

2. Objectives
• In this lecture, you will learn:
– Some relational model terminologies
– The difference between the relation schema and
relational database schema
– The properties of a relation
– Relational keys
– Views and purpose of views in relational database
2

3. Relational Model Terminology
• An entity is a person, place, event, or
thing/Object for which we intend to collect
data
• Examples:
– University -- Students, Faculty Members, Courses
– Airline -- Pilots, Aircraft, Routes, Suppliers
• A relation is a table with columns and rows.
– Only applies to logical structure of the database,
not the physical structure.

4. Relational Model Terminology
• Attribute is a named column of a relation.
• Example:
– Student -- Student Number, Name...etc
• Domain is the set of allowable values for one
or more attributes.
Attribute Domain Name Meaning Domain
Definition
Stu_id StudentID ID of a student Character:
Size 10

5. 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
– A collection of normalized relations with distinct
relation names.

6. 6
Example of Attribute Domain

7. 7
Entity and Attribute

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.

9. Definition Summary
Informal Terms Formal Terms
Table Relation
Column Header Attribute
All possible Column
Values
Domain
Row Tuple
Table Definition Schema of a Relation
Populated Table State of the Relation

10. Relation and Relational Schema
• A relation schema is the name and the list of
attributes of a relation
• Example:
– Grade (studentId, assignmentId, points, dateSubmitted)
Relational Schema

11. Properties of Relation
• 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.
• Each tuple is distinct; there are no duplicate tuples.
• Order of attributes has no significance.
• Order of tuples has no significance, theoretically.

12. Relational Keys
• Super key
– An attribute, or a set of attributes, that uniquely identifies a
tuple within a relation.
• Candidate Key
– Super key (K) such that no proper subset is a super key within
the relation.
• Candidate key, K, for a relation R has two properties
– Uniqueness - in each tuple of R, values of K uniquely identify
that tuple.
– Irreducibility - no proper subset of K has the uniqueness
property

13. Relational Key
• Super key
– Uniquely identifies each entity
• STU_NUM
• STU_NUM, STU_LNAME
• STU_NUM, STU_LNAME, STU_INIT
• Candidate key
– Minimal super key
• STU_NUM
• STU_LNAME, STU_FNAME, STU_INIT, STU_PHONE
• When a key consists of more than one attribute, it is
called a composite key

14. Example
• Which attributes of this table can be used as a candidate
key?
• BranchNo and PostalCode can be used as candidate keys.
• City attribute cannot be used as a candidate key, because it
has duplicate values.
BranchNo Street City PostalCode
B005 22 Deer Rd London SW1 4EH
B007 16 Argyll St Aberdeen AB2 3SU
B003 163 Main St Glasgow G11 9QX
B004 32 Manse Rd Bristol BS99 1NZ
B003 56 Clover Dr London NW10 6EU

15. Relational Key
• Primary Key
– Candidate key selected to identify tuples uniquely within
relation.
• Alternate Keys
– Candidate keys that are not selected to be primary key.
• Foreign Key
– Attribute, or set of attributes, within one relation that matches
candidate key of some (possibly same) relation

16. Links to Refer
• https://youtu.be/EwEY_Y2Zz0s
• https://youtu.be/RRUeFwuJ39Q