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