Business Systems Analysis
and Design
Systems Analysis and Design using
Data Modeling
-- Entity Relationship Model
Made by: Group 3
Aaditya Tanwar 2009SMF6627
Sanjiv Yadav 2009SMF6679
Shaunak Batra 2009SMF6537
Systems Development Life Cycle
(SDLC):
2
Data Modeling and Systems
Development Life Cycle:
3
Conceptual Data Modeling
A detailed model that captures the overall
structure of data in an organization
Independent of any database management
system (DBMS) or other implementation
considerations
4
Process of Conceptual Data
Modeling
5
Gathering Information for
Conceptual Data Modeling
Two perspectives
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Requirement Determination Questions for
Data Modeling
What are subjects/objects of the business?
Data entities and descriptions
What unique characteristics differentiates between subjects/objects of
the same type?
Primary keys
What characteristics describe each subject/object?
Attributes and secondary keys
How do you use the data?
Security controls and user access privileges
7
Requirement Determination Questions for
Data Modeling (cont.)
Over what period of time are you interested in the data?
Cardinality and time dimensions
Are all instances of each object the same?
Supertypes, subtypes, and aggregations
What events imply associations between objects?
Relationships and cardinalities
Are there special circumstances that affect the way events are
handled?
Integrity rules, cardinalities, time dimensions
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Entity-Relationship (E-R)
Modeling:
Entity-Relationship (E-R) Diagram
◦ A detailed, logical representation of the
entities, associations and data elements for an
organization or business
Notation uses three main constructs
◦ Data entities
◦ Relationships
◦ Attributes
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Association
between the
instances of one or
more entity types
Person, place, object, named property or
event or concept about characteristic of an
which data is to be entity
maintained
Entity type: collection
of entities with
common
characteristics
Entity instance: single
entity 10
Identifier Attributes
Candidate key
◦ Attribute (or combination of attributes) that
uniquely identifies each instance of an entity
type
Identifier
◦ A candidate key that has been selected as the
unique identifying characteristic for an entity
type also known as the Primary Key
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Multivalued Attributes
An attribute that may take on more than
one value for each entity instance
Represented on E-R Diagram by a
double-lined ellipse
12
Entity and Attribute Example
Simple attributes
Identifier attribute… Multivalued attribute…
each employee has an employee may have
a unique ID. more than one skill.
13
Degree of Relationship
Degree: number of entity types that participate in a relationship
Three cases
◦ Unary: between two instances of one entity type
◦ Binary: between the instances of two entity types
◦ Ternary: among the instances of three entity types
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Examples:
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Cardinality
The number of instances of entity B that can or must be associated with
each instance of entity A
Minimum Cardinality
◦ The minimum number of instances of entity B that may be associated with
each instance of entity A
Maximum Cardinality
◦ The maximum number of instances of entity B that may be associated with
each instance of entity A
Mandatory vs. Optional Cardinalities
◦ Specifies whether an instance must exist or can be absent in the relationship
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Cardinality Symbols
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Unary Relationship – Many to Many
Example
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Binary Relationship Examples
Mandatory cardinalities:
One optional, one mandatory cardinality:
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Associative Entities
An entity type that associates the instances of one or
more entity types and contains attributes that are
peculiar to the relationship between those entity
instances
An associative entity is:
◦ An entity
◦ A relationship
This is the preferred way of illustrating a relationship
with attributes
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A relationship with an attribute
…as an associative entity
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Ternary relationship
…as an associative entity
22
A relationship
that itself is
related to
other entities
via another
relationship
must be
represented
as an
associative
entity.
23
Supertypes and Subtypes
Subtype: a subrouping of the entities in an
entity type that shares common attributes
or relationships distinct from other
subtypes
Supertype: a generic entity type that has a
relationship with one or more subtype
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Rules for Supertype/Subtypes Relationships
Total specialization: an entity instance of the supertype
must be an instance of one of the subtypes
Partial specialization: an entity instance of the supertype
may or may not be an instance of one of the subtypes
Disjoint: an entity instance of the supertype can be an
instance of only one subtype
Overlap: an entity instance of the supertype may be an
instance of multiple subtypes
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Example of Supertype / Subtype
Hierarchy:
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Example:
A company database needs to store information
about employees (identified by ssn, with salary
and phone as attributes); departments (identified
by dno, with dname and budget as attributes);
and children of employees (with name and age
as attributes). Employees work in departments;
each department is managed by an employee; a
child must be identified uniquely by name when
the parent (who is an employee; assume that
only one parent works for the company) is
known. We are not interested in information
about a child once the parent leaves the
company.
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References:
Pin, Peter; Shah, Chen. The Entity Relationship model: Toward a unified
view of data. ACM Transactions on Database Systems.1976.
Andrew Burton-Jones, Ron Weber. Understanding Relationships with
Attributes In Entity-relationship Diagrams. 1997.
Article by Pedersen, Alf A. Entity Relationship Modelling. 2004.
www.devarticles.com/c/a/Development-Cycles/Entity-Relationship-
Modeling/
ABRIAL, J.R. Data semantics. In Data Base Management, North-Holland
Pub. Co., Amsterdam, 1974.
http://www.databasedesign.co.uk/bookdatabasesafirstcourse/chap3/chap3.
htm
http://www.getahead-direct.com/gwentrel.htm
Logical Data Structures (LDSs) - Getting started.
http://www.cems.uwe.ac.uk/~tdrewry/lds.htm
www.wikipedia.org
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Thank You
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