UML

UML is a standard language for specifying, visualizing, constructing, and documenting the artifacts of software systems.

UML was created by Object Management Group (OMG) and UML 1.0 specification draft was proposed to the OMG in January 1997.

UML diagrams are not only made for developers but also for business users, common people and anybody interested to understand the system. The system can be a software or non software. So it must be clear that UML is not a development method rather it accompanies with processes to make a successful system.

At the conclusion, the goal of UML can be defined as a simple modeling mechanism to model all possible practical systems in today’s complex environment.

UML have several types of diagrams that can be used to describe different points of views. Let’s talk about some of these. 

Class Diagrams

The purpose of a class diagram is to depict the classes within a model. In an object oriented application, classes have attributes (member variables), operations (member functions) and relationships with other classes. The UML class diagram can depict all these things quite easily. The fundamental element of the class diagram is an icon the represents a class. According to Martin (2010), class icon is simply a rectangle divided into three compartments. The topmost compartment contains the name of the class. The middle compartment contains a list of attributes (member variables),

and the bottom compartment contains a list of operations (member functions). In many diagrams, the bottom two compartments are omitted. Even when they are present, they typically do not show every attribute and operations. The goal is to show only those attributes and operations that are useful for the particular diagram.

Example of Class Diagram

UML Use Case Diagrams

Use cases are powerful tools for analysts to use when partitioning the functionality of a system. Use case relationships and the corresponding diagrams help analysts to structure use cases such that their textual descriptions contain a minimum of redundant information; thus making the whole text document much easier to maintain. But use cases are not design tools. They do not specify the structure of the eventual software, nor do they imply the existence of any classes or objects. They are purely functional descriptions written in a formalism that is completely separate from software design.

Use cases separate the system into actors and use cases. Actors represent roles that can are played by users of the system. Those users can be humans, other computers, pieces of hardware, or even other software systems. The only criterion is that they must be external to the part of the system being partitioned into use cases. They must supply stimuli to that part of the system, and the must receive outputs from it. 

Use cases (“Engineering Notebook”, 1998) describe the behavior of the system when one of these actors sends one particular stimulus. This behavior is described textually. It describes the nature of the stimulus that triggers the use case; the inputs from and outputs to other actors, and the behaviors that convert the inputs to the outputs. The text of the use case also usually describes everything that can go wrong during the course of the specified behavior, and what remedial action the system will take.

Example: Clerk checks out an item.

Activity Diagram

            Activity diagrams are normally used for business process modeling, for modeling the logic captured by a single use case or usage scenario, or for modeling the detailed logic of a business rule.  Although UML activity diagrams could potentially model the internal logic of a complex operation it would be far better to simply rewrite the operation so that it is simple enough that you don’t require an activity diagram. In many ways UML activity diagrams are the object-oriented equivalent of flow charts and data flow diagrams (DFDs) from structured development.

Booking a Concert Ticket

Reference

http://www.objectmentor.com/resources/articles/umlClassDiagrams.pdf      class diagram

http://www.objectmentor.com/resources/articles/usecases.pdf   use case

http://d0server1.fnal.gov/www/online_computing/meetings/Weekly/M_990507/StateTutorial.pdf   state

http://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep03/f_umlbasics_db.pdf

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