ERwin
Methods Guide
© 1997 by Logic Works, Inc.
ERwin Version 3.0
Methods Guide
Logic Works, Inc.
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Princeton, NJ 08540
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ERwin Methods Guide
Contents
Preface |
iii |
Intended Audience ................................................................................................ |
iv |
About this Guide ................................................................................................... |
iv |
Typographical Conventions................................................................................... |
v |
Related Documentation.......................................................................................... |
v |
Information Systems, Databases, and Models |
9 |
What’s In This Chapter?......................................................................................... |
9 |
What is Data Modeling?....................................................................................... |
10 |
Data Modeling Sessions ....................................................................................... |
12 |
Sample IDEF1X Modeling Methodology............................................................ |
14 |
Logical Models...................................................................................................... |
16 |
Physical Models .................................................................................................... |
17 |
Benefits of Modeling in ERwin............................................................................ |
18 |
Constructing a Logical Model |
19 |
What’s In This Chapter?....................................................................................... |
19 |
The Entity-Relationship Diagram........................................................................ |
20 |
Validating the Design of the Logical Model....................................................... |
24 |
Data Model Example............................................................................................ |
25 |
The Key-Based Model |
27 |
What’s In This Chapter?....................................................................................... |
27 |
Understanding Keys............................................................................................. |
28 |
Relationships and Foreign Key Attributes.......................................................... |
32 |
Rolenames ............................................................................................................. |
36 |
Naming and Defining Entities and Attributes |
37 |
What’s In This Chapter?....................................................................................... |
37 |
Naming Entities and Attributes .......................................................................... |
38 |
Entity Definitions.................................................................................................. |
40 |
Attribute Definitions ............................................................................................ |
43 |
Rolenames ............................................................................................................. |
44 |
Contents ∙ i
ERwin Methods Guide |
|
Definitions and Business Rules ............................................................................ |
46 |
Refining Model Relationships |
47 |
What’s In This Chapter? ....................................................................................... |
47 |
Relationship Cardinality ....................................................................................... |
48 |
Referential Integrity............................................................................................... |
51 |
Additional Relationship Types............................................................................. |
56 |
Many-to-Many Relationships ............................................................................... |
57 |
N-ary Relationships............................................................................................... |
60 |
Recursive Relationships ........................................................................................ |
62 |
Subtype Relationships........................................................................................... |
64 |
Normalization |
71 |
Introduction ........................................................................................................... |
71 |
Overview of the Normal Forms ........................................................................... |
72 |
Common Design Problems................................................................................... |
73 |
Unification.............................................................................................................. |
84 |
How Much Normalization Is Enough?................................................................ |
86 |
ERwin Support for Normalization....................................................................... |
88 |
Creating a Physical Model |
91 |
What’s In This Chapter? ....................................................................................... |
91 |
Creating a Physical Model.................................................................................... |
92 |
Denormalization .................................................................................................... |
93 |
Dependent Entity Types |
95 |
Classification of Dependent Entities.................................................................... |
95 |
Glossary of Terms |
97 |
Index |
101 |
ii ∙ Contents