Use Case Diagrams

Graphic Element	Description
Text description of the illustration uml001.gif	Primary Use Cases and a Model Diagram In each use case diagram, the primary use case is instigated, used, or called by an actor (stickman), which can be a human user, an application, or a subprogram. The actor is connected to the primary use case by a solid line. The primary use case is depicted as an oval (bubble) enclosing the use case action, which in this example, is "DELETE the row". All primary use cases are described in a use case "model" diagram.
Text description of the illustration adl049_o.gif	Secondary Use Cases Primary use cases may require other operations to complete them. In this diagram fragment: SELECT a LOB is one of the suboperations, or secondary use cases, needed to complete INSERT a row, when using the INSERT AS SELECT statement. The downward line from the secondary use case leads to the other required operations (not shown).
Text description of the illustration adl052_o.gif	Drop Shadows A 'secondary' use case with a drop shadow expands into its own use case diagram, thus making it easier to: Understand the logic of the operation Continue a complex operation across multiple pages The use case model diagrams use drop shadows fopr each primary use case. For example, see Figure 10-1. When There's More Than One Way... In other diagrams, where there may be a number of ways, say, to INSERT values into a LOB, the diagrams use (a), (b), (c) (in note format), where (a) is one primary (separate) use case diagram, (b) another, and so on. In the online versions of these diagrams, these are clickable areas that link to the related use case.
Text description of the illustration uml005.gif	Here is a form of the a, b, c convention. There are three ways to create a table containing LOBs.
Text description of the illustration uml006.gif	Using Notes in the Use Case Diagrams This use case fragment shows one of the uses of a note. The note is in a box that has one corner turned down. Here, the note is used to present one of the three ways to create a table containing LOBs. Note boxes can also present an alternative name. Note boxes can qualify or add more detail to requirements for the use case action..

Graphic Element	Description
Text description of the illustration uml008.gif	Dashed Lines (Black) Black dashed arrows in the use case diagram indicate dependency. In this example: free a temporary LOB, requires that you first create a temporary LOB In other words, do not execute the free operation on a LOB that is not temporary. The target of the arrow shows the operation that must be performed first.

Graphic Element Text description of the illustration uml011.gif

Description - Black and Gray Dashed Lines The black dashed line and arrow indicate that the targeted operation is required. The gray dashed line and arrow indicate that the targeted operation is optional. In this example, executing write append, on a LOB requires that you first SELECT a LOB You may optionally choose to OPEN a LOB or get chunk size Note that if you do OPEN a LOB, you must CLOSE it.

Graphic Element Text description of the illustration uml007.gif

Branched Lines Mean OR Conditions In this case the branching paths of an OR condition are shown. In invoking the view, you can choose to list all the attributes or view one or more attributes. The grayed arrow indicates that you can stipulate which attributes you want to view.

Graphic Element	Description
Text description of the illustration uml013.gif	Use Case Model Diagrams Use case model diagrams summarize all the use cases in a particular domain, such as Internal Temporary LOBs. When diagrams are too complex to fit on one page, they are divided into two parts, as shown here. No sequence is implied in this division.
Text description of the illustration uml014.gif	This marker indicates that the diagram is continued.