tailieunhanh - PATTERNS OF DATA MODELING- P51

PATTERNS OF DATA MODELING- P51: 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. | 238 Appendix C Glossary multiple inheritance a generalization for which an entity type inherits information from multiple supertypes. Contrast with single inheritance. multiplicity the number of occurrences of one entity type that may connect to an occurrence of a related entity type. Multiplicity is a constraint on the size of a collection. Contrast with cardinality. n-ary relationship a relationship involving three or more relationship ends. non-identifying relationship a relationship that does not contribute to the primary key of an entity type. Contrast with identifying relationship. normal form a guideline for relational database design that increases data consistency. See denormalization. null a special value denoting that an attribute value is unknown or not applicable. Object Constraint Language OCL a language for defining constraints within the UML. You can also use the OCL to navigate data models. Object Management Group OMG a standards forum that is the owner of the UML. OMG acronym Object Management Group. ordered relationship a relationship that has an ordering imposed on a many end. path a sequence of traversals of relationships and generalization levels. pattern a model fragment that is profound and recurring. A pattern is a proven solution to a specified problem that has stood the test of time. primary key a candidate key that is preferentially used for cross-table references. Normally an entity type should have a primary key an entity type can have at most one primary key. See alternate key candidate key and foreign key. qualified relationship a relationship in which one or more attributes called qualifiers disambiguate the entities for a many relationship end. qualifier an attribute that selects among the entities at a many relationship end. referential integrity a database mechanism that ensures that data references really exist and that there are no dangling foreign keys. relational database a database in which the data are perceived as tables.