The Data Model Resource Book, Volume 3: Universal Patterns for Data Modeling

Silverston c01.tex V2 - 11/21/2008 2:57am Page 28

28 Chapter 1 ■ Introduction

entity occurrence. The exclusive arc is represented by a curved line going

through two or more relationship lines and an ‘‘XOR’’ symbol on the line

that connects the relationships. Figure 1-8 shows an example of an exclusive

arc. The relationships are read as ‘‘Each INVENTORY ITEM must be either

located at one and only FACILITY or must be located within one and only

one CONTAINER, but not both.’’ This communicates that inventory items are

stored at one of two types of levels: They are either located at facilities such as

a warehouse or stored within containers such as a bin that is located within a

facility.

INVENTORY ITEM

INVENTORY ITEM ID ID (PK)

FACILITY ID ID (FK)

CONTAINER ID ID (FK)

CONTAINER

CONTAINER ID ID (PK)

FACILITY

FACILITY ID ID (PK)

the storage container for

located withinlocated at

located at

the location for the location of

XOR

Figure 1-8 Exclusive Arcs

Example Data in Illustration Tables

Many parts of the data models are illustrated via tables that contain possible

values for attributes. Each illustration table is normally defined to show

specific worked examples, or in other words, we illustrate the pattern by

showing instances of the entities and attributes to provide examples of how a

pattern may look when populated. Often one illustration table is not enough

and the pattern needs to be explained by two or ...