E r model

1. Entity Relationship Models
Sumant Kulkarni, Yogalakshmi
fsumant.kulkarni, [email protected]
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2. Agenda
IUse of ER Model for Conceptual Models
IBasic Structure of ER Model
IExample of ER model development
IDiscussion
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3. ER Model
IConcise description of data requirements of the users
IFor better visualization of entities and relations
IUnderstanding concepts involved in the miniworld
INo implementation details
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4. Basic Elements of ER Model
The miniworld is described in terms of:
IEntity
IAttribute
IRelationships
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5. Description of an Example of a miniworld
Every student is identied 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 oered by one or more professors (combined).
So, each faculty member spends a specic number of hours on
the course he oers. A professor can be involved in oering
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 specic 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 identication
numbers for every faculty member, lab and project.
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8. Elements of ER Model
IEntity
IAttribute
IComposite versus Simple (Atomic) Attributes
ISingle-Valued versus Multivalued Attributes
IStored versus Derived Attributes
INull Attributes (NA)
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9. Elements of ER Model
IEntity Set
IKey Attributes of an Entity Type (uniqueness constraint)
IValue Sets (Domains) of Attributes.
IValue Set of composite attribute.
V=P(V1)XP(V2)X:::XP(Vn)
whereP(Vi) is the powerset ofVi.
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10. Exploring Relationships
IWhat is Relationship?
IRelationship Types
IRelationship Instances
IRelationship Sets
IParticipation
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11. Exploring Relationships
IRelationship Degree (unary, binary, ternary)
IRelationship as Attributes
IRole Names and Recursive Relationships
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12. Constraints on Relationship Types
ICardinality Ratios for Binary Relationships
ITotal participation (existence dependency)
IPartial participation
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13. Attributes of Relationship Types
Migration of Attributes from Relationship Types
IMigration in 1:1 Relationship type
IMigration in 1:N Relationship type.
IMigration in M:N Relationship type
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14. Weak Entity Types
IOwner (identifying) entity type
IIdentifying relationship
IA weak entity type always has a total participation constraint.
IA weak entity type normally has Partial key
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15. Summery of Symbols
Figure:
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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
IElmasri, R. and Navathe, S.B.Fundamentals Of Database
Systems. Pearson Education
IChen, P.P.The Entity Relationship Model - Towards a Unied
View of Data. ACM Transactions on Database Systems. 1976
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19. Any Questions/Inputs/Suggestions?
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