1. Data Modeling
Advanced Concepts

2. Common Modeling Situations
Unary relationships
Binary relationships
Ternary relationships
Attributive or Weak Entities
Associative or Intersection Entities
Supertypes and Subtypes

3. Degree of Relationship
Number of entity types that participate in a relationship
Three cases
Unary
A relationship between two instances of one entity type
Binary
A relationship between the instances of two entity types
Ternary
A simultaneous relationship among the instances of three entity types
Not the same as three binary relationships

4. Figure 10-6 Example relationships of different degrees

5. Which type of relationship is this?
Customers
(Parent)
Orders
(Child)
cust_id cust_name
100 Slick Willy, Inc.
200 George_W, Co.
300 Gore, Ltd. …
ord no cust_id ord_date
Sep-2000
Nov-2000
Dec-2000
Dec-2000 …
A binary one to many relationship.
A customer places many orders. An order is placed by only one customer.
“An instance of the entity customer is related to one or many instances of orders. An instance of order is related to only one instance of customer.”

6. Which type of relationship is this?
Are these the same statements?
A CD appears on several orders.
An order may have many CDS on it.
Binary many to many

7. Entity-Relationship (E-R) Modeling Key Terms
Attributive or Weak Entity
An entity than cannot exist without the existence of another entity.
Examples. What would be a weak entity for
A DePaul Course?
An employee?
A product?
Associative entity
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

8. Multivalued Attributes
How do we model the situation where an entity has an attribute describing it, but
The attribute may take on more than one value for each entity instance
The multivalued attribute can be represented on an E-R Diagram in two ways:
double-lined ellipse
weak entity

9. Depicting Multivalued Attributes
See pages
Which way is better?
What should the identifier of DEPENDENT be?

10. Depicting Associative Entities
See pages
Which way is better?
What should the identifier of CERTIFICATE be?

11. Depicting M:M relationships
Create an intersection entity (line item).
Move the “M’s” are adjacent to the intersection entity.
3. The “1” side goes on the original entities.
Binary many to many

12. Supertypes and Subtypes
A supertype is a generic entity type that has a relationship with one or more subtypes.
A subtype is a subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings.
Examples
Customers and Preferred Customers
Students, graduate, PhD, undergraduate, full-time, part-time
Why bother?
Sometimes it is a better representation of reality. It is useful to know if two entities are very similar, i.e. one is a special type of another. There are implications for database design also, e.g. where to store common attributes.

13. Supertype/Subtype Rules Specialization
Does the instance of the supertype have to be a member of a subtype?
If yes, Total Specialization (double line)
If no, Partial Specialization (single line)
It says supertypes are allowed not to belong to a subtype.
Examples—which rule of specialization applies?
Customers and Preferred Customers
Students, graduate, PhD, undergraduate, full-time, part-time

14. Supertype/Subtype Rules Disjoint/Overlap
Can an instance of the supertype be a member of more than one subtype?
If yes, Overlap (letter “o”)
If no, Disjoint (letter “d”)
Examples—which rule of specialization applies?
Friends, countrymen, Romans
Students, graduate, PhD, undergraduate, full-time, part-time

15. Supertype/Subtype Example
Page 326.
Is this diagram correct?
What about the
“Is assigned”
relationship?

16. Another example. Page 327. Does the model allow for:
Student Employees?
Staff members teaching?
Simultaneous Grad/undergrad students?
Student employees: Yes. The overlap below PERSON.
Staff members teaching? No. the d below EMPLOYEE.
Simultaneous grad/u/g? No. the d below STUDENT.
A “non-employee/alumnus/student” PERSON = a PERSON who is neither a STUDENT, nor a EMPLOYEE, nor an ALUMNUS.
A “non-employee/alumnus/student” PERSON?

17. Business Rules Entity integrity Referential integrity Domains
Each entity instance has a unique identifier.
The identifier value cannot be empty.
Referential integrity
The value or existence of an attribute in one relation depends on the value or existence of the same attribute occurring in another relation
More on this in IS422
Domains
Triggering operations

18. Domains
The set of all data types and ranges of values that an attribute can assume
Several advantages
Verify that the values for an attribute are valid
Ensure that various data manipulation operations are logical
Help conserve effort in describing attribute characteristics

19. Triggering Operations
An assertion or rule that governs the validity of data manipulation operations such as insert, update and delete
Includes the following components:
User rule
Statement of the business rule to be enforced by the trigger
Event
Data manipulation operation that initiates the operation
Entity Name
Name of entity being accessed or modified
Condition
Condition that causes the operation to be triggered
Action
Action taken when the operation is triggered
Where would you say the responsibility for data integrity lies—in the application programs or the database management system?
The DBMS. Closer to the eventual source. Else, you must remember to enforce integrity in EVERY application.