Creating UML Class Diagrams: Understanding Classes, Attributes, Methods, and Relationships, Study notes of Digital Signal Processing

Download Creating UML Class Diagrams: Understanding Classes, Attributes, Methods, and Relationships and more Study notes Digital Signal Processing in PDF only on Docsity! A Brief Guide to the UML Class Diagrams Introduction The Unified Modeling Language (UML) is a graphical language for creating diagrams that are useful in the software development process. The UML provides a set of standard graphical symbols and the rules for combining them. The UML is process and implementation language independent. The UML provides symbols to support various views of the system. In all, there are nine diagram types included in the UML:  Class diagrams,  Object diagrams,  Use case diagrams,  Sequence diagrams,  Collaboration diagrams,  State-chart diagrams,  Activity diagrams,  Component diagrams, and  Deployment diagrams. In this guide, we will be concerned with class diagrams, which provide a structural view of the system. Class Diagrams Class diagrams are perhaps the most common type of diagram used in modeling object-oriented systems. A class diagram shows a set of classes, interfaces, collaborations, and dependencies. In addition, notes and constraints can appear on a class diagram. You use class diagrams to show the static structure of your system. A class is represented by a box that is divided horizontally into three sections. The top section contains the class name, the middle section contains the class attributes and the bottom section contains the class methods. An example of a class diagram for a Time class is shown below. hour minute second setTime() displayMilitaryTime() displayStandardTime() Time Class Name The class name appears in the top section of the class box and consists of text. The class name is a noun or noun phrase. Typically, the first letter of each word in the phrase is capitalized. - 1 - Class Attributes The middle section of the class box contains the class attributes. An attribute represents some property of the class. The attribute name consists of text and is a noun or noun phrase. Typically, the first letter of each word in the phrase is capitalized, except the first. You can, optionally, specify the type of the attribute and possibly a default value. For example, to specify that the attribute hour is of type integer and has an initial value of 12, replace hour in the above diagram with hour : Integer = 12 . Collections (or arrays) of attributes are indicated by giving the multiplicity. Refer to the discussion of multiplicity in the Association section below. Nota Bene: By specifying the type and default values, you are increasing the information content of the diagram at the possible expense of cluttering the diagram. This same comment is applicable to other optional information. Class Methods The bottom section of the class box contains the class methods. A method is an abstraction of something that an object can do, or have done to it. The method name consists of text and is a verb or verb phrase, followed by left and right parenthesis. Typically, you capitalize the first letter of each word in the name, except the first. You can, optionally, specify the names, types and default of all method arguments as well as the return type of functions. For example, a full specification of the setTime() method might look like setTime( newHour : Integer = 12, newMinute : Integer = 0, newSecond : Integer = 0 ) Visibility The UML provides symbols to indicate the visibility of attributes and methods. The following symbols, when place immediately before either an attribute name or method name, define the visibility of the attribute or name: + public - private # protected For example, to give the attribute minute protected visibility, you would write # minute. Scope You can specify the scope of an attribute using the UML. By default, an attribute has instance scope. That is, each object created from the class has its own value for the attribute. You can give an attribute class scope, by underlining the attribute name (and type and default value if present). The most common use for class scope is to share a private variable among all instances of the class. You might do this, for example, if you needed to give each instance a unique identifier. Relationships The UML provides graphic symbols to represent the following relationships:  Dependency  Association  Generalization between classes. - 2 -