1. Enhanced/Extended Relationship-Diagram
Indra Budi

2. Enhanced-ER (EER) Model Concepts
Includes all modeling concepts of basic ER
Additional concepts: subclasses/superclasses, specialization/generalization, categories, attribute inheritance
The resulting model is called the enhanced-ER or Extended ER (E2R or EER) model
It is used to model applications more completely and accurately if needed
It includes some object-oriented concepts, such as inheritance 2

3. Subclass Entity type describes: Example: ‘EMPLOYEE’
Type of entity
The entity set
Example: ‘EMPLOYEE’
Employee can be sub-grouped into:
Secretary
Engineer
Technician
Manager
These are called the subclass of EMPLOYEE entity type. 3

4. Super-class
EMPLOYEE entity type is the super class of engineer, secretary & technician class.
Subclass represent the same mini-world entity of the superclass, but in a distinct specific role.
These are also called IS-A relationships (SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, …).
Entity in a subclass must be a member of a superclass, but not vice-versa! Example…? 4

5. Type inheritance
An entity that is member of a subclass inherits all attributes of the entity as a member of the superclass
It also inherits all relationships 5

6. Specialization
Is a process of defining a set of subclasses of an entity type (the superclass)
Secretary, engineers, & technician are specialization of EMPLOYEE based on job type attribute 6

7. Cont’d
May have several specialization based on different characteristics
Example, EMPLOYEE can be subclass-ed into Salaried_Employee and Hourly_Employee 7

8. Fig 4.1 8

9. Notations from the EER diagram
Subset symbol ⊂
Specific attributes, or local attributes
Specific relationships
Superclass/subclass EMPLOYEE/Secretary resembles 1:1 relationship at the instance level, of one entity. 9

10. Fig 4.2 10

11. Benefit of Specialization
Define a set of subclasses of an entity type
Establish additional specific attributes with each subclass
Establish additional specific relationship types between each subclass and other entity types or other subclasses
Refer to the EER diagram…! 11

12. Generalization
Identify common features (attributes), and generalize into a superclass
Example: truck & car can be generalized into VEHICLE
Inverse of the specialization process 12

13. 13

14. Constraints Constraints in Specialization Hierarchies & Lattices
Specialization in conceptual data modeling 14

15. Predicate defined subclasses
Also called condition-defined subclasses
Conditioned by a defining predicate at the superclass
Example, JobType = ‘Secretary’
Place attribute name on the arc 15

16. 16

17. User defined subclass
Membership is specified individually for each entity by the user
Not by any condition that may be evaluated automatically
Example: Manager subclass 17

18. Disjointness constraints
Subclasses of a specialization must be disjoint
An entity can only be at most one of the subclass
Look at the EER diagram
Use (d) 18

19. Overlap
The same entity may be a member of more than one subclass of the specialization
Use the (o)
Example, a person can be:
A student
A faculty member
An alumni 19

20. 20

21. Completeness constraints
Total specialization:
Every entity in the superclass must be a member of some subclass
Example, the Salaried_Employee and Hourly_Employee
Shown using double line 21

22. Partial specialization:
Allows an entity not to belong to any subclass
Example:
Manager
Job type
Use single line 22

23. Rules
Deleting entity from a superclass  deletes it also from the subclasses
Inserting in a superclass, when attribute defined is filled  must insert to the proper subclass as well
Inserting in superclass of total specialization  must insert into at least one subclass 23

24. Hierarchy & Lattice
Hierarchy: a subclass only participates in one class/subclass relationship
Example: Vehicle with Car and Trucks
Lattice: a subclass can participate in more than one class/subclass relationship
Example: an Engineering Manager, must be an Engineer, and also a Manager!
The concept of multiple inheritance 24

25. 25

26. Figure 4.7 26

27. More Explanation of the EER Diagram
Leaf node: class that has no subclasses
An entity may exist in several leaves
Example, a student as Graduate_Student and a Teaching_Assistant
Multiple inheritance:
Student_assistant
But the ‘Person’ attribute is only inherited once 27

28. UNION Types Using Categories
Engineering_Manager has 3 distinct relation, each relation has 1 superclass
In our new case, a subclass has a single relationship with 3 distinct superclass.
The subclass represent collection of objects, which we call union type or category 28

29. Figure 4.8 29

30. Explanation
A category OWNER is a union subclass of COMPANY, BANK and PERSON
Use the (U) symbol
Registered_Vehicle is a union subclass of Car & Truck 30

31. The difference?
Engineering_Manager must exist in all three superclass: Manager, Engineer, Salaried_Employee
Owner, must exist in only one superclasses
Engineering_Manager: inherited all superclasses attributes
Owner, selective attribute inheritance, depending on the superclass 31

32. Partial Category
Partial category, may or may not participate in the relation 32

33. Total Category Must be one of the superclasses
Example: A building and a lot must be a member of PROPERTY
May be represented as a generalization (d), especially when the similarity is numerous 33

34. Fig 4.10 34

35. Formal Definitions of EER Model (1)
Class C: A set of entities; could be entity type, subclass, superclass, category.
Subclass S: A class whose entities must always be subset of the entities in another class, called the superclass C of the superclass/subclass (or IS-A) relationship S/C:
S ⊆ C
Specialization Z: Z = {S1, S2,…, Sn} a set of subclasses with same superclass G; hence, G/Si a superclass relationship for i = 1, …., n.
G is called a generalization of the subclasses {S1, S2,…, Sn}
Z is total if we always have:
S1 ∪ S2 ∪ … ∪ Sn = G; Otherwise, Z is partial.
Z is disjoint if we always have:
Si ∩ S2 empty-set for i ≠ j;
Otherwise, Z is overlapping. 35

36. Formal Definitions of EER Model (2)
Subclass S of C is predicate defined if predicate p on attributes of C is used to specify membership in S; that is, S = C[p], where C[p] is the set of entities in C that satisfy p
A subclass not defined by a predicate is called user-defined
Attribute-defined specialization: if a predicate A = ci (where A is an attribute of G and ci is a constant value from the domain of A) is used to specify membership in each subclass Si in Z
Note: If ci ≠ cj for i ≠ j, and A is single-valued, then the attribute-defined specialization will be disjoint.
Category or UNION type T
A class that is a subset of the union of n defining superclasses D1, D2,…Dn, n>1:
T ⊆ (D1 ∪ D2 ∪ … ∪ Dn) A predicate pi on the attributes of T.
If a predicate pi on the attributes of Di can specify entities of Di that are members of T.
If a predicate is specified on every Di: T = (D1[p1] ∪ D2[p2] ∪…∪ Dn[pn]
Note: The definition of relationship type should have 'entity type' replaced with 'class'. 36

37. Alternative Diagrammatic Notations
Symbols for entity type / class, attribute and relationship
Displaying attributes
Notations for displaying specialization / generalization
Various (min, max) notations
Displaying cardinality ratios 37

38. Exercise Domain Entity Relationship Entity set
a property or description of an entity
a set of possible values for an attribute.
an object in the real world that is distinguishable from other objects such as the green dragon toy.
an association among two or more entities.
a collection of similar entities such as all of the toys in the toy department.
a collection of similar relationships
a key constraint that indicates that one entity can be associated with many of another entity.
a key constraint that indicates that many of one entity can be associated with many of another entity.
an entity that cannot be identi.ed uniquely without considering some primary key attributes of another identifying owner entity.
maximum number of instances of an entity that can participate in an instance of a relationship
is the least number of instances of an entity that can participate in an instance of a relationship
Domain
Entity
Relationship
Entity set
One-to-many relationship
Relationship set
Attribute
Minimum cardinality
Weak entity
Maximum cardinality
Many-to-many relationship 38

39. Exercise (cont.) 39

40. Exercise (cont.) Develop ER-Diagram based on following facts !
Manufacturers have a name, which we may assume is unique, an address, and a phone number
Product have a model number and a type (e.g., television set). Each product is made by one manufacturer, and different manufacturers may have different products with the same model number. However, you may assume that no manufacturer would have two products with the same model number.
Customers are identified by their unique social security number. They have addresses, and physical addresses. Several customers may live at the same (physical) address, but we assume that no two customers have the same address.
An order has a unique order number, and a date. An order is placed by one customer. For each order, there are one or more products ordered, and there is a quantity for each product on the order. 40

41. Exercise (cont.)
A company database needs to store information about employees (identifed by ssn, with salary and phone as attributes), departments (identifed 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 identi.ed 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.
Draw an ER diagram that captures that information. 41