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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 - Analysts Experience
(Page 21 of 21 )

Patterns are studies of small, specific domains of a larger ER model, with one (or a few) in- and outgoing links to surrounding domains of the ER model. An experienced analyst will immediately recognize a given domain in the model as something she has studied before, and knows about. She can therefore bring added value into the ER model by discussing the domain with the business, and ask ‘difficult’ questions, based on limitations that are obvious with regards to the patterns of that domain, and which the analyst brings with her, in her experience.

Main point: If you go through a development cycle for a new application, it is because you want something others do not have. You do it in order to gain some competitive edge, or you are realizing a very new business idea. Either way, copying something old is not too smart. However, keeping patterns, that cover separate smaller domains of the model, at work, may build you a system that is not only something unique, but also contains flexibility based on earlier, hard-earned experience. 

Important Analyst Ethics - Reminders
You have done the job, and a complete Entity Relationship model, with Function Hierarchies, Events, and Business Constraints are all in place. And, when conditions change, the customer needs to order a rewrite, is he happy? No. If he knows he can just create a new customer type in the CUSTOMER_TYPE table and then go on, without calling you, will he be happy then? I think so.

This is the responsibility of the system analyst: giving the customer flexibility for future growth and change, without those costly rewrites. As a consultant you may disagree, you may just love those rewrites as an income-generating tool! But I assure you in the long run, you will win by building flexibility and room for change for your customer.

I just read somewhere on the Internet that in the good old days, a dissatisfied customer would tell his frustration to 6 others. In the days of the Internet, he will tell it to 6,000 others.

I would try to avoid that. 

http://www.databasedesign-resource.com

er-modeling@databasedesign-resource.com


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