Chapter 4

• What is a subclass in the context of entity types?

  A subclass is a meaningful sub-grouping of an entity type.
• How can the EMPLOYEE entity type be further grouped?

  It can be grouped into SECRETARY, ENGINEER, TECHNICIAN, etc., based on job type.
• What are the two bases for grouping EMPLOYEEs?

  Based on job type and method of pay.
• What do EER diagrams extend from?

  EER diagrams extend ER diagrams.
• What is the relationship between subclasses and superclasses?

  Each subclass is a subset of its superclass.
• What is the superclass for the subclasses SECRETARY, TECHNICIAN, and MANAGER?


  EMPLOYEE is the superclass.
• What type of relationship do subclasses and superclasses represent?

  They represent superclass/subclass relationships.
• What does the IS-A relationship signify in subclasses?

  It signifies that a subclass is a specific type of its superclass.
• Can an entity exist in the database solely as a member of a subclass?

  No, it must also be a member of the superclass.
• What happens if an entity is a salaried employee and an engineer?

  It belongs to both subclasses: ENGINEER and SALARIED_EMPLOYEE.
• What is attribute inheritance in superclass/subclass relationships?


  A subclass inherits all attributes and relationships from its superclass.
• What attributes do subclasses like SECRETARY inherit from the EMPLOYEE superclass?


  They inherit Name, SSN, Birthdate, and Address.
• What is specialization in the context of subclasses?


  • Specialization defines a set of subclasses from a superclass.
  • Based on distinguishing characteristics of entities in the superclass.
  • Example: {SECRETARY, ENGINEER, TECHNICIAN} is a specialization of EMPLOYEE based on job type.
• How can specialization be represented in EER diagrams?


  It can be represented diagrammatically with subclasses branching from the superclass.
• What are specific or local attributes in subclasses?


  They are attributes unique to the subclass, such as TypingSpeed for SECRETARY.
• What is generalization in the context of subclasses?


  Generalization is the process of combining several classes with common features into a superclass.
• How can CAR and TRUCK be related in terms of generalization?


  They can be generalized into a superclass called VEHICLE.
• What are the types of specialization/generalization constraints?


  1. Disjointness Constraint

  • Specifies subclasses must be disjoint.

  1. Completeness (Exhaustiveness) Constraint

  • Total: Every entity must belong to a subclass.
  • Partial: An entity may not belong to any subclass.
• What does the disjointness constraint specify?


  It specifies that an entity can be a member of at most one subclass.
• What does the completeness constraint indicate?


  It indicates whether every entity in the superclass must belong to some subclass.
• What are the four types of specialization/generalization?


  1. Disjoint, total
  2. Disjoint, partial
  3. Overlapping, total
  4. Overlapping, partial
• What is a shared subclass?


  A shared subclass is a subclass that can inherit from more than one superclass.
• What is the difference between specialization and generalization processes?


  Specialization is top-down, while generalization is bottom-up.
• What is the EER UNIVERSITY example about?

  • Tracks three types of persons: employees, alumni, and students.
  • Employees can be faculty, staff, or student assistants.
  • Students can be graduate or undergraduate.
• What is a category or UNION TYPE?

  A category is a subclass in more than one distinct superclass/subclass relationship.
• How does a category differ from a shared subclass?

  A category must exist in at least one superclass, while a shared subclass must exist in all superclasses.
• What are alternative diagrammatic notations in EER modeling?

  • ER/EER diagrams are specific notations for displaying concepts.
  • UML class diagrams are a popular alternative notation.
• What are the formal definitions of the EER model?


  • Specialization: A set of subclasses with a common superclass.
  • Generalization: Combining classes into a superclass.
  • Predicate-defined subclass: Membership specified by a condition.
  • User-defined subclass: Membership specified individually.
• What is the significance of the EER model in data modeling?


  • Introduces class/subclass relationships.
  • Explains specialization and generalization.
  • Discusses inheritance and constraints on EER schemas.