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Entity Relationship Modeling


Entity Relationship Modeling (ER modeling) is by far the most common way to express the analytical result of an early stage in the construction of a new database. In this ebook, Alf Pedersen describes the principles for ER modeling, as well as the most important terms used in modeling a new database.

Author Info:
By: Alf A. Pedersen
Rating: 4 stars4 stars4 stars4 stars4 stars / 89
April 05, 2004
TABLE OF CONTENTS:
  1. · Entity Relationship Modeling
  2. · The Entity
  3. · Other Business Contacts
  4. · Attributes in entities
  5. · Business Rules
  6. · Three types of relationships
  7. · Supplier Entity
  8. · A Weak Relation
  9. · A Useful Relation
  10. · Involuted (or recursive) relationships
  11. · Many-to-Many
  12. · The Database Analysis Team - A Teamwork
  13. · Level of Knowledge
  14. · Experience vs. Inexperience
  15. · Complete Model?
  16. · Building Queries
  17. · Other Common Errors in ER Modeling
  18. · Second Normal Violation
  19. · More Specific
  20. · Generic or Specific Models?
  21. · Analysts Experience

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Entity Relationship Modeling - Generic or Specific Models?
(Page 20 of 21 )

We will look into the use of generic or specific database models in this keynote. There are many analysts who advocate for using generic ER models to build a system, while others favor building it costumer-specific. Actually, I slightly disagree with both directions. 

I have studied many generic models. One common denominator is that generic models try to capture everything imaginable in a certain field of business, like financials, production, etc. If you need to cover everything imaginable, you are probably already a customer of Oracle Financials, Peoplesoft, or some other high-end ERP system.

The reason for starting a project involving ER modeling, design, development and deployment of an application, is that the business wants to build something unique; a new way of treating customers, new supply logistics, or anything else that gives it a competitive edge. A generic model will involve many entities, relationships, and probably business rules that are not relevant to the business. It means developing functions that will never be used, an extended database with tables that are never accessed, triggers that fire and execute nothing. Even this code-


begin
  null;
end
;

Will have some impact on performance if it is executed often enough each day. A model specifically designed for the business sounds good. However, you have a chance of narrowing your scope too much, so that you build inflexible limitations into the system. Refer to the keynote on Analysis Trap 2. An experienced analyst brings with him into the project a perspective based on earlier experience. He is able to recognize patterns in different areas of the business domain. 

The customer is an area for which a pattern can be given. There are many common questions regarding customers, which can be reflected in a recognizable pattern. 

How we build a sales order is also a common pattern. At some point there is a customer involved, the order is about one or more products, it should be effectuated and delivered, someone has to pay, etc.


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