This document discusses entity relationship (ER) models. It describes ER models as concise descriptions of user data requirements that help visualize entities and relationships in a domain. The basic elements of an ER model are entities, attributes, and relationships. An example ER model is presented for a student academic information system that models students, courses, professors, labs, and projects as entities and how they relate. Key concepts like entity sets, relationship types, participation constraints, and weak entity types are also explained.

1. Entity Relationship Models
Sumant Kulkarni, Yogalakshmi
{sumant.kulkarni, j.yogalakshmi}@iiitb.org
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2. Agenda
Use of ER Model for Conceptual Models
Basic Structure of ER Model
Example of ER model development
Discussion
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3. ER Model
Concise description of data requirements of the users
For better visualization of entities and relations
Understanding concepts involved in the miniworld
No implementation details
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4. Basic Elements of ER Model
The miniworld is described in terms of:
Entity
Attribute
Relationships
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5. Description of an Example of a miniworld
Every student is identified by his student number. The system
also knows about his Date of Birth, current and permanent
addresses, and his joining date. Every student registers for
some courses or works for projects or does both. Student can
either audit the course or take it for credit. He obtains grades
for the courses he takes on credit. These grades are available
for all the subjects the student has taken on credit till now.
These credits decide whether he has passed or failed in the
subject.
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6. Description of an Example of a miniworld
Every course is offered by one or more professors (combined).
So, each faculty member spends a specific number of hours on
the course he offers. A professor can be involved in offering
many courses. Every course belongs to a stream. It also has a
name, unique course number. There are some credit
associated with the course.
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7. Description of an Example of a miniworld
Professor may be in-charges of a lab. A lab can have one or
more in-charges. A lab can have multiple projects running
under it from specific start dates. If a student opts to work for
a projects, then depending upon the need of the project, he
has to spend some know amount of time on the project.
Similar to the student id, there will be unique identification
numbers for every faculty member, lab and project.
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8. Elements of ER Model
Entity
Attribute
Composite versus Simple (Atomic) Attributes
Single-Valued versus Multivalued Attributes
Stored versus Derived Attributes
Null Attributes (NA)
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9. Elements of ER Model
Entity Set
Key Attributes of an Entity Type (uniqueness constraint)
Value Sets (Domains) of Attributes.
Value Set of composite attribute.
V = P(V 1)XP(V 2)X ...XP(Vn)
where P(Vi) is the powerset of Vi.
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10. Exploring Relationships
What is Relationship?
Relationship Types
Relationship Instances
Relationship Sets
Participation
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11. Exploring Relationships
Relationship Degree (unary, binary, ternary)
Relationship as Attributes
Role Names and Recursive Relationships
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12. Constraints on Relationship Types
Cardinality Ratios for Binary Relationships
Total participation (existence dependency)
Partial participation
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13. Attributes of Relationship Types
Migration of Attributes from Relationship Types
Migration in 1:1 Relationship type
Migration in 1:N Relationship type.
Migration in M:N Relationship type
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14. Weak Entity Types
Owner (identifying) entity type
Identifying relationship
A weak entity type always has a total participation constraint.
A weak entity type normally has Partial key
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15. Summery of Symbols
Figure: Summery of Symbols of E-R modeling
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16. Student Academic Information System as ER Model
Let us list all the entities from the description given....
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17. Relations between Entities
Let us List down....
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18. References
Elmasri, R. and Navathe, S.B. Fundamentals Of Database
Systems. Pearson Education
Chen, P.P. The Entity Relationship Model - Towards a Unified
View of Data. ACM Transactions on Database Systems. 1976
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19. Any Questions/Inputs/Suggestions?
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