PATTERNS OF DATA MODELING- P45: 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. | 208 Chapter 16 Relational Database Design UML model IDEF1X model ListedCourse ListedLesson listedCourselD listedLessonlD listedCourseName listedLessonName scheduledDuration listedCourselD FK sequenceNumber Figure Ordered relationship Mapping. Use the same mapping as without ordering. The source entity type plus a sequence number is unique. would have been correct to bury the relationships but from an architectural point of view I wanted to isolate dependencies between subject areas. Mapping Qualified Relationships There are four possible situations for qualified relationships. One-to-optional after qualification. This is the most common situation Figure . The underlying relationship is one-to-many without the qualifier and you should bury the source entity type key and the qualifier in the many table. The combination of the source entity type plus the qualifier is unique. UML model Airline PublishedFlight airlinelD IDEF1X model airlineCode airlineName publishedFlightID frequency effectiveDate expirationDate airlinelD FK flightNumber Figure Qualified relationship one-to-optional Mapping. Bury fields in the many table. The source entity type plus the qualifier is unique. Mapping Qualified Relationships 209 Optional-to-optional after qualification. This situation is also common Figure . Bury the source entity type key and the qualifier in the table that is many without qualification. In the example one record the root of the tree has a null parentID keeps the source entity type plus the qualifier from being unique. As an alternative you can promote the relationship to a table and then the qualified relationship has a unique key. UML model Tree Node IDEF1X model treeID rootID FK nodeID parentID FK nodeName Figure Qualified relationship optional-to-optional Mapping. Bury fields in the many table. The source entity type plus the qualifier is not unique. Many-to-optional after qualification. These .
