PATTERNS OF DATA MODELING- P17: Models provide the means for building quality software in a predictable manner. Models let developers think deeply about software and cope with large size and complexity. Developers can think abstractly before becoming enmeshed in the details of writing code. Although models are beneficial, they can be difficult to construct. That is where patterns come in. Patterns provide building blocks that help developers construct models faster and better. | Chapter Summary 61 Table Summary of the Directed Graph Templates Template name Synopsis UML template Use when Frequency Simple DG Treats all nodes the same. 1 1 11 11 Edges are unimportant nodes have the same kind of data. The DG is acyclic. Occasional Structured DG Differentiates leaf nodes from branch nodes. HzL Edges are unimportant branch nodes and leaf nodes have different data. The DG is acyclic. Occasional Node and edge DG Treats nodes and edges as peers. Nodes and edges can both have data there can be multiple edges between a pair of nodes. Common Connection DG Promotes the connection between a node and an edge to an entity type. 1 1 1 1 1 1 There is data for the connection itself as well as for nodes and edges. Occasional Simple DG changing over time Stores multiple variants of a DG. Extract a particular DG by specifying a time. 1 T rj Illi A DG changes over time edges are unimportant. The DG is acyclic. Seldom Node and edge DG changing over time Stores multiple variants of a DG. Extract a particular DG by specifying a time. A DG changes over time edges are important. Occasional Note This table can help you choose among the directed graph templates. 62 Chapter 3 Directed Graph Template Bibliographic Notes Page 89 of Hay-1996 has an example of projects that involve the node and edge directed graph. References Hay-1996 David C. Hay. Data Model Patterns Conventions of Thought. New York New York Dorsett House 1996. 4 Undirected Graph Template The undirected graph is also a term from graph theory. An undirected graph is a set of nodes and a set of edges. Each edge connects two nodes which may be the same . The nodes of an undirected graph can have any number of edges. Undirected graphs arise for applications with important topology or connectivity. For example the network of members on the LinkedIn Web site is an undirected graph. Figure shows two examples of undirected graphs. Figure Sample undirected graphs. An undirected graph is a set of .
