The UML notation is a fusion of the notations of Booch, OMT, OOSE and others. UML is designed to be readable on a large variety of media, such as whiteboards, paper, restaurant tablecloths, computer displays, black and white printouts, etc. The designers of the notation have sought simplicity above all — UML is straightforward, homogeneous, and consistent. Awkward, redundant and superfluous symbols have been eliminated, in order to favor a better visual rendering.
UML focuses on the description of software development artifacts, rather than on the formalization of the development process itself, and it can therefore be used to describe software entities obtained through the application of various development processes. UML is not a rigid notation: it is generic, extensible, and can be tailored to the needs of the user. UML does not look for over-specification — there is not a graphical representation for all possible concepts. In the case of particular requirements, details may be added using extension mechanisms and textual comments. Great freedom remains for tools to filter the information displayed. The use of colors, drawings, and particular visual attributes is left up to the user.
This chapter gives an overview of the semantics of UML's model elements, and aims to introduce the main concepts of modeling, articulating them in terms of the UML notation. The visual and modeling elements are introduced together, using the UML notation as a foundation for the presentation of their semantics.
UML defines nine types of diagrams to represent the various modeling viewpoints. The presentation order of the various diagrams does not reflect the order of implementation in a real project, but simply follows a textbook approach that attempts to minimize prerequisites and cross-references.
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