Guide to Applying the UML

CHAPTER 6 Structural (Static) Modeling (p.212)
This chapter provides essential rules, principles, and style guidelines for composing UML structural or static models within the context of the roadmap, including class and object diagrams and their elements. Structural modeling is concerned with modeling the structural or static dimension of a system - the elements and their relationships that constitute a system - and is used for system, subsystem, and class speci.cation within the roadmap to capture in a speci.cation model how the construct will satisfy its requirements. Structural modeling is also used to determine which elements and their relationships collaborate to constitute the construct, and how these elements interact to provide functionality to end users. A speci.cation model consists of class, object, sequence, collaboration, state, and activity diagrams and their model elements. Our goal, in this chapter, is to gain more depth in understanding the UML notation and the roadmap concerning the structural or static aspect of speci.cation models.


6.1. Class Diagrams

A class diagram depicts the static structure of an entity using classi.ers and relationships. An entity is a classiffer, for example, a system, subsystem, or class.
6.1.1. CLASSIFIERS
A classiffer is a concept that de.nes structural features and behavioral features, and has various types of relationships. A feature is a property encapsulated within a model element, an atomic constituent of a model. Structural features de.ne the static features of a model element. Behav ioral features de.ne the dynamic features of a model element. A classiffer may contain other classiffers. It owns its contents and de.nes a namespace, a part of a model in which a name may be uniquely de.ned and used. An element may access any contents of its own namespace or a containing namespace. Specific types of classi.ers include classes, actors, use cases, data types, interfaces, components, nodes, subsystems, and artifacts.

A classiffer is depicted as a vertex or node, including an icon or twodimensional symbol that may contain other elements. Other information is depicted as strings or sequences of characters attached to nodes. A classi.er is named using an optional stereotype or list of stereotypes followed by an optional visibility symbol followed by the classiffer name string followed by an optional property. Not all details of a modeling element need to be depicted on a diagram, only those that are relevant to the purpose of the diagram.

A stereotype is used to classify (brand) or mark a model element so that it may be given a speci.c meaning. A stereotype is depicted as a text string keyword enclosed in guillemets («») or double-angle brackets preceding or above the name of the element. Multiple stereotypes may be applied to an elements depicted vertically one below the other or preceding each other. A user-de.ned icon may be used to signify a stereotype. The guillemets and the stereotype icon may be depicted simultaneously; however only one is required. The icon is placed in the upper right corner near the name of the element, or the entire base model element symbol is collapsed into an icon containing the element name or with the name above or below the icon, and other information contained by the base model element symbol is suppressed. When multiple stereotypes are used for an element, the icons are omitted.