The document discusses relational database concepts including: 1) A relational database represents data using relations (tables) with rows and columns, where each row represents a fact and each column represents an attribute. 2) Entity-relationship (ER) modeling represents real-world entities and relationships between entities using entity types, relationship types, and attributes. 3) Relationship types associate multiple entity types and have structural constraints like cardinality ratios that specify the minimum and maximum number of relationships an entity can participate in.

1. Module II: Relational
Database & ER Model

2. Contents
Relational System, Codd’s Rule, Relational
Model, Optimization, Tables and Views,
Entity, Types of Entity, Weak Entity Attributes
, Entity sets , Entity – Relationship Diagrams.

3. Relational Model Concepts
• The relational Model of Data is based on the
concept of a Relation.
• A Relation is a mathematical concept based
on the ideas of sets.
• The strength of the relational approach to
data management comes from the formal
foundation provided by the theory of relations.

4. INFORMAL DEFINITIONS
• RELATION: A table of values
– A relation may be thought of as a set of rows.
– A relation may alternately be though of as a set of columns.
– Each row represents a fact that corresponds to a real-world
entity or relationship.
– Each row has a value of an item or set of items that uniquely
identifies that row in the table.
– Sometimes row-ids or sequential numbers are assigned to
identify the rows in the table.
– Each column typically is called by its column name or column
header or attribute name.

5. FORMAL DEFINITIONS
• A Relation may be defined in multiple ways.
• The Schema of a Relation: R (A1, A2, .....An)
Relation schema R is defined over attributes A1,
A2, .....An
For Example -
CUSTOMER (Cust-id, Cust-name, Address,
Phone#)
Here, CUSTOMER is a relation defined over the four
attributes Cust-id, Cust-name, Address, Phone#, each
of which has a domain or a set of valid values. For
example, the domain of Cust-id is 6 digit numbers.

6. Example -

7. Typical DBMS Functionality
• Define a database : in terms of data types,
structures and constraints
• Construct or Load the Database on a
secondary storage medium
• Manipulating the database : querying,
generating reports, insertions, deletions
and modifications to its content
• Concurrent Processing and Sharing by a
set of users and programs – yet, keeping all
data valid and consistent

8. CODD’S RULES
1 Information Rule
2 Guaranteed Access Rule
3 Systematic Treatment of Nulls Rule
4 Active On-line catalog based on the relational model
5 Comprehensive Data Sub-language Rule
6 View Updating Rule
7 High-Level Insert, Update and Delete
8 Physical Data Independence
9 Logical Data Independence
10 Integrity Independence
11 Distribution Independence
12 No subversion Rule

9. Definitions
• An entity is an object in the miniworld.
• An attribute of an entity can have a value
from a value set (domain)
• Each entity belongs to some one entity
type s.t. entities in one entity type have the
same attributes (so each entity type is a
set of similar entities).

10. Definitions (con’t)
• A key attribute of an entity type is one
whose value uniquely identifies an entity
of that type.
• A combination of attributes may form a
composite key.
• If there is no applicable value for an
attribute that attribute is set to a null value.

11. Entity Type / Entity Set
Entity Type (Intension): EMPLOYEE
Attributes: Name, Age, Salary
Entity Set (Extension): e1 = (John Smith, 55, 80000)
e2 = (Joe Doe, 40, 20000)
e3 = (Jane Doe, 27, 30000)
.
.
.

12. Attributes
• Attributes can be
– composite / simple (atomic)
– single-valued / multivalued
– stored / derived
– key / nonkey.

14. EMPLOYEE
Name, SSN, Sex, Address, Salary, Birthdate, Department,
Supervisor, {Works on ( Project, Hours)}
WORKS_FOR
N 1
Name SSN . . .
EMPLOYEE DEPARTMENT
Relationship instances of WORKS_FOR:
{(KV, CS), (Pan, EE), . . .}

15. ER Diagram for COMPANY Database

16. Relationship Type
• A relationship type R among n entity types
E1,…,En is a set of relationship instances
ri, where each ri associates n entities (e1,
…,en), s.t. each ej ∈ Ej. Informally, a
relationship instance is an association of
entities, with exactly one entity from each
participating entity type.

17. Relationship Type (con’t)
• The degree n of a relationship type is the
number of participating entity types.
• In the ER model relationships are
explicitly represented.

18. Entity Roles
• Each entity type in a relationship type
plays a particular role that is described by
a role name. Role names are especially
important in recursive relationship types
where the same entity participates in
more than one role:
Employee
Supervisor 1 N Supervisee
Supervision

19. Weak Entity Type
• A weak entity type is one without any key
attributes of its own. Entities belonging to
a weak entity type are identified by being
related to another entity type ( called
identifying owner) through a relationship
type ( called identifying relationship), in
combination with values of a set of its own
attributes (called partial key). A weak entity
type has total participation constraint w.r.t.
its identifying relationship.

20. Relationship Attributes
• Relationship types can have attributes as
well. in case of 1:1 or 1:N relationships,
attributes can be migrated to one of the
participating entity types.

21. Structural Constraints
• Structural constraints of a relationship
type:
– Cardinality ratio: Limits the number of
relationship instances an entity can participate
in, eg. 1:1, 1:N, M:N
– Participation constraint: If each entity of
an entity type is required to participate in
some instance of a relationship type, then that
participation is total; otherwise, it is partial.

22. Structural Constraint Min, Max
• A more complete specification of the
structural constraint on a relationship type
can be given by the integer pair (min,
max), which means an entity must
participate in at least min and at most max
relationship instances.

24. A ternary relationship generally represents
more information than 3 binary relationships