Tuesday, September 25, 2012

Part 4.1 Conceptual Data Modeling

4. Data Modeling

4.1 Conceptual Data Modeling
      4.1.1 Introduction to Conceptual Data Model
      4.1.2 Stages in Conceptual Modeling
      4.1.3 Components of a Conceptual Data Model
      4.1.4 ER Modeling Basic Concepts
      4.1.5 Enhanced ER Modeling
      4.1.6 Guidelines for ER Modeling
4: 4.1 Conceptual Data Model
Conceptual Data Model
A conceptual schema or conceptual data model is a map of concepts and their relationships. This describes the semantics of an organization and represents a series of assertions about its nature. Specifically, it describes the things of significance to an organization (entity classes), about which it is inclined to collect information, and characteristics of (attributes) and associations between pairs of those things of significance (relationships).
A conceptual data model identifies the highest-level relationships between the different entities.
Features of conceptual data model include:
Includes the important entities and the relationships among them.
No attribute is specified.
No primary key is specified.
4.1.2 Stages in Conceptual Modeling

Main stages in conceptual modeling are as follows:

--  Identification of requirements (done in previous lesson)
--  Designing of solutions
--  Evaluation of solutions
4.1.3 Components of a Conceptual Data Model
  
4.1.4 ER Modeling Basic Concepts
ER Model

The ER model is a conceptual model
Describes data as entities, relationships and attributes
No standard notation for displaying ER diagrams
(We will choose one among several alternatives for this presentation)
Entity
An entity is a “thing” in the real world with an independent existence
An entity may be an object with a physical existence
For example, person, car, house
An entity may be an object with a conceptual existence
For example, company, job, university-course

 
4.1.5 Enhanced ER Modeling
  
Enhanced ER Model, Includes all the modeling concepts of the ER model

In addition, it includes the following concepts:

  • Subclass & super-class
  • Specialization & generalization
  • Category
  • Attribute & relationship inheritance
Subclass & Super-class


  • In many cases an entity type has numerous sub-groupings of its entities that are meaningful and need to be represented explicitly because of their significance to the database application. Each of these sub-groupings are called subclass.
  • The entity type on which these subclasses are formed is called super-class
  • The relationship between a super-class and any one of its subclasses is called a super-class/subclass, a class/subclass or an IS-A (or IS-AN) relationship, e.g., a SECRETARY IS-AN EMPLOYEE
  • A member entity of a subclass represents the same real-world entity as some member of the super-class, but in a distinct specific role
Specialization (Top to Bottom Approach)


Specialization is the process of defining a set of subclasses of an entity type


In addition, it allows us to do the following:
  •  Establish additional specific attributes with each subclasses
  •  Establish additional specific relationship types between each subclass and other entity types or other subclasses
Generalization (Bottom to Top Approach)


Generalization refers to the process of defining a generalized entity type from the given entity types


Generalization process can be viewed as being functionally the inverse of the specialization process   
 


  A specialization lattice with multiple inheritance for a UNIVERSITY database.