1. Chapter 4: Enhanced Entity-Relationship (EER) Modeling
Data Modeling and Database Design
Chapter 4: Enhanced Entity-Relationship (EER) Modeling

2. Remember! Presentation Layer ER Diagram  Contains hashes and oval
Design-specific ER Diagram (Coarse-granularity)  Uses (min, max) notation  Maps deletion rules
Design-specific ER Diagram (Fine-granularity)  Maps attribute characteristics into ER diagram  Decomposes multi-valued attributes  Decomposes m:n relationships
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

3. Enhanced Entity-Relationship (EER) Model
Enhanced Entity-Relationship (EER) modeling is an extension to the ER modeling that incorporates additional constructs
Central construct Superclass/subclass (SC/sc) relationship
More specifically:
Specialization/generalization
Categorization
Aggregation
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

4. Superclass/Subclass Relationship (SC/sc)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

5. An Instance Diagram
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

6. Think About It…
Theoretically, one has three choices of modeling furniture/chair/table/sofa
Model three separate entity types for chair, table, and sofa, and create three separate relationship types with the entity type store
Model furniture as an entity type with an attribute called furniture_type; then chair, table, and sofa would be values of that attribute
Model furniture as a superclass/subclass
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

7. SC/sc Relationships There are two basic kinds of Sc/sc relationships
Specialization/Generalization: One superclass (SC) is related to one or more subclasses (sc)
Categorization: One subclass (sc) is related to one or more superclasses (SC)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

8. Vignette 1
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

9. Modeling Vignette 1: Alternative 1
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

10. Modeling Vignette 1: Alternative 2
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

11. Modeling Vignette 1: Alternative 3
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

12. Properties of SC/sc Relationships
An entity that exists in a subclass can be associated with only one superclass entity
An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of an associated superclass
An entity that is a member of a superclass can be optionally included as a member of any number of its subclasses
It is not required that every member of a superclass be a member of a subclass
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

13. Properties of SC/sc Relationships (continued)
Type Inheritance Property: A subclass inherits all the attributes of the superclass to which it is related
In addition, it will also inherit all the relationship types in which the superclass participates
A subclass may also have its own specific attributes in addition to the attributes inherited
Likewise, a subclass may have its own specific relationship(s) with other entity types (i.e., inter-entity class relationships)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

14. Note That…
The cardinality ratio of any SC/sc relationship is always 1:1
The participation of the subclass in a SC/sc relationship is always total
A subclass inherits all attributes as well as all relationship types that a superclass possesses (type inheritance property)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

15. Specialization and Generalization
Specialization is the process of generating subgroups (‘sc’s) of a generic entity class (SC) by specifying the distinguishing properties (attributes) of the subgroups (= top-down approach)
Generalization, on the other hand, crystallizes the common properties (attributes) shared by a set of entity types (‘sc’s) into a generic entity type (SC) (= bottom-up approach)
Notation: circle + fork (indicating subset)
Read: “is-a”
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

16. Specialization and Generalization (continued)
Completeness Constraint The participation of the superclass in a specialization/ generalization is referred to as the completeness constraint and can assume one of two values: total or partial
Total specialization means that every entity of the superclass must participate in this specialization/ generalization relationship (indicated by a solid line from the superclass to the specialization/generalization symbol (i.e., the circle))
Partial specialization means that there may be entities present in the superclass that do not participate in this specialization/generalization (indicated by a dotted line)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

17. Specialization and Generalization (continued)
Disjointness Constraint Used to specify that the subclasses of a specialization must be:
Disjointed (indicated by ‘D’), i.e., an entity of the superclass cannot be a member of more than one subclass
Overlapped across subclasses (indicated by ‘O’)
Please note that you have to specify both: completeness and disjointness constraints!
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

18. Notation
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

19. An EER Model of Vignette 1
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

20. Sample Data Sets For EER Model of Vignette 1
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

21. An Extension of Vignette 1: Multiple Specializations
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

22. Sample Data Sets For Vignette 1 Extension
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

23. An EER Model of Vignette 2
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

24. Specialization/Generalization Hierarchy
Example of a Hierarchy: [STUDENT -> STUDENT_ATHLETE -> FOOTBALL_PLAYER -> {DEFENSIVE_PLAYER, OFFENSIVE_PLAYER}] shows a 3-level hierarchy
Inheritance A subclass inherits the attributes and relationship types of not just the immediate parent, but also of the predecessor superclasses in the hierarchy all the way up to the root of the specialization hierarchy
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

25. An EER Model of Vignette 3
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

26. Specialization/Generalization Lattice
In a specialization lattice, an entity type can participate as a subclass in more than one specialization (i.e., a child can have more than one parent)
Inheritance The subclass will inherit all the attributes and relationship types from the superclasses of all the specializations participating in the lattice and the predecessor hierarchy of all these superclasses
This is called multiple type inheritance, and the subclass in the lattice is referred to as a shared subclass
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

27. The Categorization Construct
A categorization occurs when a subclass is associated with more than one superclass of different entity types
The subclass is called category
An entity that is a member of the category (subclass) must exist in ONLY ONE of the superclasses in the categorization relationship
Example: A financial donor can be an individual, a company, or a foundation  no “is-a” relationship!
Notation: ‘U’ (= union, the subclass is a subset of the union of the superclasses)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

28. Categorization Example
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

29. Characteristics of a Categorization
There is only one subclass in each categorization
The cardinality ratio is 1:1 within and across the SC/sc relationship
The participation of the subclass in the categorization is always total
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

30. Characteristics of a Categorization (continued)
Each superclass may exhibit either total or partial participation
A category can either be:
A total category (i.e., the category is the union of all the superclass entities)
A partial category (i.e., the category is a true subset of the union of all the superclass entities)
A category possesses the property of selective type inheritance (i.e., it inherits attributes of one entity type only)
Often a unique identifier for a category must be manufactured (which is called a surrogate key)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

31. Sample Data Sets For Categorization Example
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

32. Choosing the Appropriate EER Construct
Exercise:
Part1: Consider an automobile dealership in the state of Texas; the dealership typically stocks cars, trucks, vans, and sport utility vehicles (SUVs)
Part 2: Not all vehicles in the dealership are registered vehicles though
How would we model REGISTERED_VEHICLE?
One exception exists in which a categorization and a generalization/specialization are mutually substitutable constructs: in the case of a total category!
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

33. Choosing the Appropriate EER Construct (continued)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

34. Choosing the Appropriate EER Construct (continued)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

35. Choosing the Appropriate EER Construct (continued)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

36. Choosing the Appropriate EER Construct (continued)
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

37. The Aggregation Construct
An aggregation allows us to model a “whole/part” relationship as an “is-a-part-of” relationship between a subclass and a superclass
An entity in the aggregate contains superclass entities from ALL SC/sc relationships in which it participates
Inheritance: Selective type inheritance connotes the inheritance of attributes and relationships from ALL superclass entities contained in the specific aggregation
Notation: ‘A’
Read: “is-part-of”
Note that an aggregate can never be partial
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

38. An Example of Aggregation
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

39. An Aggregation Hierarchy
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

40. Aggregation Versus Categorization
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

41. A Fine-granular Design-Specific EER Diagram for Vignette 3
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

42. A Presentation Layer EER Diagram For Bearcat, Inc.
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling

43. A Fine-granular Design-Specific EER Diagram For Bearcat, Inc.
Chapter 4 – Enhanced Entity-Relationship (EER) Modeling