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

Silverston c04.tex V2 - 11/21/2008 3:02am Page 164

164 Chapter 4 ■ Hierarchies, Aggregations, and Peer-to-Peer Relationships

knowledge (such as specifying one-to-many recursive relationships); how-

ever, the real strength of this pattern is that it maintains a level of flexibility

that allows multiple different ways of creating hierarchies, aggregations or

peer-to-peer relationships. The significance of this pattern is that it explicitly

addresses resolving many-to-many recursive re lationships. The pattern sup-

ports hierarchies, aggregates, and peer-to-peer relationships. In this section we

described why it is important to understand the underlying rules that support

peer-to-peer relationships, such as transitive dependency. Finally, this pattern

is also significant because we show how you can mix both many-to-many and

one-to-many r elationships.

This pattern helps you when you need to support a complex environment

where you need to capture many different ways that an entity is related to

itself. This approach often provides a good basis for implementing databases in

fairly dynamic environments with the exception of not easily accommodating

new types of recursive relationships that may emerge (we will address this in

the next pattern). If you need the flexibility of having multiple many-to-many

recursive relationships and you know all of the different recursive relationships

that you wish to capture, ...