1. Review of Week 1 Database DBMS File systems vs. database systems
Evolution of data models
Basic data modeling components
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2. Module 2 Database Design Concepts

3. Chapter 4 Entity Relationship (ER) Modeling
Module 2: Database Design Concepts

4. Introduction to the E-R Model
Data modeling is about documenting rules and policies that govern data.
Entity relationship data model is a detailed logical representation of the entities, associations and data elements for an organization or business arena.
Entity-relationship diagram is a graphical representation of an E-R model.
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5. Business Rules
Statements that define or constrain some aspect of the business
Assert business structure
Control/influence business behavior
Expressed in terms familiar to end users
Automated through DBMS software
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6. Entity Relationship (ER) Model
ERD represents the conceptual database as viewed by end user
ERDs depict the ER model’s three main components:
Entities
Attributes
Relationships
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7. Entity (Entity Type)
Refers to the entity set and not to a single entity occurrence
Is a collection of entities that share common properties or characteristics
Corresponds to a table and not to a row in the relational environment
Entity name, a noun, is usually written in capital letters
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8. What Should an Entity Be?
Should be:
An object that will have many instances in the database
An object that will be composed of multiple attributes
An object that we are trying to model
Should not be:
A user of the database system
An output of the database system (e.g. A report)
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9. Attributes Characteristics of entities Classifications of attributes:
Simple versus composite attribute
Single-valued versus multi-valued attribute
Stored versus derived attributes
Identifier attributes
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10. The Attributes of the STUDENT Entity
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11. Domains Attributes have a domain: Attributes may share a domain
The attribute’s set of possible values
Attributes may share a domain
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12. Primary Keys (Identifiers)
Identifier (key) - an attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Candidate key – an attribute that could be a key…satisfies the requirements for being a key
Underlined in the ER diagram
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13. Characteristics of Identifiers
Will not change in value
Will not be null
No intelligent identifiers (e.g. containing locations or people that might change)
Substitute new, simple keys for long, composite keys
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14. The CLASS Table (Entity) Components and Contents
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15. A Multivalued Attribute in an Entity
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16. Resolving Multivalued Attribute Problems
Although the conceptual model can handle multivalued attributes, you should not implement them in the relational DBMS
Within original entity, create several new attributes, one for each of the original multivalued attribute’s components
Create a new entity composed of original multivalued attribute’s components
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17. Splitting the Multivalued Attribute into New Attributes
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18. A New Entity for a Multivalued Attribute’s Components
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19. Derived Attributes
Attribute whose value may be calculated (derived) from other attributes
Need not be physically stored within the database
Can be derived by using an algorithm
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20. Depiction of a Derived Attribute
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21. Relationships Association between entities Participants:
Entities that participate in a relationship
Relationships between entities always operate in both directions
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22. Connectivity or Cardinality
One – to – One: Each entity instance will have exactly one related entity instance
One – to – Many: An entity instance on one side can have many related entity instances, but an entity instance on the other side will have a maximum of one related entity instance
Many – to – Many: Entity instances on both sides can have many related entity instances on the other side
Established by very concise statements known as business rules
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23. Cardinality in an ERD
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24. Relationship Participation
Optional: One entity occurrence does not require a corresponding entity occurrence in a particular relationship
Mandatory: One entity occurrence requires a corresponding entity occurrence in a particular relationship
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25. Mandatory Participation
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26. Optional Participation
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27. Cardinality in an ERD
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28. Strong vs. Weak Entities
Strong entities
exist independently of other types of entities
has its own unique identifier
Weak entity
dependent on a strong entity…cannot exist on its own
Has primary key that is partially or totally derived from the parent entity in the relationship
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29. A Weak Entity in an ERD
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30. Weak Entity Data Sample
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31. Relationship Degree
Indicates number of associated entities or participants
Unary relationship – Association is maintained within a single entity
Binary relationship - Two entities are associated
Ternary relationship - Three entities are associated
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32. Three Types of Relationships
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33. The Implementation of a Ternary Relationship
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34. Recursive Relationships
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35. 1:1 Recursive Example
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36. M:N Recursive Example
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37. 1:M Recursive Example
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38. Composite Entities Also known as bridge entities, associative entities
Composed of the primary keys of each of the entities to be connected
May also contain additional attributes of the relationship
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39. M:N Relationship
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40. Converting M:N Relationship with Composite Entity
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41. Composite Entity Data Sample
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42. Developing an ER Diagram
Database design is an iterative rather than a linear or sequential process
Iterative process
Determine all of the entities
Determine the attributes for each entity
Determine the central or key entity and start the diagram with it
Determine the relationship between each of the entities
Complete the diagram with cardinality, etc.
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43. Completed Tiny College ERD
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44. Activity of ER Modeling
View “diagramming a database”
Class discussion of ERD
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45. Wrap Up Assignment 2-1 Look ahead of assignment 3-1
Problem 5 on Page 172
Look ahead of assignment 3-1
Search for a business problem
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