tailieunhanh - PATTERNS OF DATA MODELING- P23

PATTERNS OF DATA MODELING- P23: 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. | 7 Summary of Templates Table through Table summarize the mathematical templates. Table Tree Templates Template Synopsis UML diagram Use when Frequency Hardcoded tree Specifies a type sequence one for each level of the hierarchy. H 1 . The levels in a tree are known and ordered. Seldom Simple tree Treats all nodes the same. 1 1 11 11 A tree concerns only data structure. Common Structured tree Differentiates leaf nodes from branch nodes. i Branch nodes and leaf nodes differ. Common Overlapping tree Permits a node to belong to multiple trees. r i A node can belong to more than one tree. Occasional Tree changing over time Stores variants of a tree over time. iiii There is history to record. Occasional Degenerate node and edge Groups a parent with its children. i i i i r i There is data for the parent-child grouping. Rare 91 92 Chapter 7 Summary of Templates Table Directed Graph Templates Template Synopsis UML diagram 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-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 a node-edge connection to an entity type. 1 1 1 1 1 1 Connections have data. Occasional Simple DG changing over time Stores variants of a DG over time. 1 T rj Illi There is history to record edges are unimportant. The DG is acyclic. Seldom Node-edge DG changing over time Stores variants of a DG over time. There is history to record edges are important. Occasional 93 Table Undirected Graph Templates Template Synopsis UML diagram Use when Frequency Node-edge UDG Treats nodes and edges as peers. No edge connects to the same node. Occasional Connection UDG Promotes a .