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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 - Experience vs. Inexperience
(Page 14 of 21 )


The difference between an experienced and an unexperienced analyst can make great differences on the finished work. While an unexperienced analyst will try to fit the business’ points of view into the E-R model, the experienced analyst will start to doubt some points of view, remembering her experiences from two years back, in a similar situation.

This phase in the project is not about making nice models; it is about making models that work, and making models that will work also if the business perspective changes, somewhere in time. It will. It always does. Building flexibility into a model is really quite simple: Follow the rules for the five Normal Forms (do at least 3NF!), and you have already asked a lot of vital questions, securing flexibility. If you want an in-depth study of the five Normal Forms, go to our Lectures section on our website, www.databasedesign-resource.com.

The sooner we can ask, and collect answers, to questions about the business, the faster the analysis progress will be. I must emphasize the importance of delivering results to your customer as fast as you can, without compromising quality; of course, it is the best way of making repetitive business too, as well as marketing.

Analysis trap 1 - Modeling with incompleteness

You may be asked: ‘We need a system for reporting quarterly balances’.  (This example is from a real world situation that eventually went wrong):

entity relationship

This was the first suggestion, which obviously will not pass the test of even the First Normal form. They ended up with this:

entity relationship

Nice enough.


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