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1.1.3 Types of Hierarchies > 1.1.3 Types of Hierarchies - Pg. 20

1 . 1 D e f i n i n g Tr e e a n d H i e ra rc h i e s 5 1.1.3 Types of Hierarchies Getting away from looking at the world from the viewpoint of a casual mathematician, let's look at it from the viewpoint of a casual database sys- tems designer. What kinds of data situations will I want to model? Looking at the world from a very high level, I can see four kinds of modeling problems. 1. Static nodes and static edges. For example, a chart of accounts in an accounting system will probably not change much over time. This is probably best done with a hierarchical encoding scheme rather than a table. We will talk about such encoding schemes later. Static nodes and dynamic edges, for example, an Internet Newsgroup message board. Obviously, you cannot add a node to a tree without adding an edge, but the content of the messages (nodes) never changes once they are posted, but new replies can be posted as subordinates to any existing message (edge). Dynamic nodes and static edges. This is the classic organizational 2. 3.