Software design is the important phase of system design. This part shows how the system will work and describes the structure of software. Software structure determines how the system will provide the design function to the user. Software design can be visualized through Visual Modeling using UML.

Visual modeling is the process of taking the information from the model and displaying it graphically using some sort of standard set of graphical elements. A standard is vital to realizing one of the benefits of visual modeling i.e. communication. Communication between users, developers, analysts, testers, managers and anyone else involved with a project is the primary purpose of visual modeling. UML is a standard that has been adopted by majority of the industry as well as the standards governing boards such as ANSI and the Object Management Group (OMG). UML allows people to develop several different types of visual diagrams that represent various aspects of the system.

Use Case diagrams show the interaction between use cases, which represent system functionality, and actors, which represent the people or systems that provide or receive information from the system. Use cases represent the requirements of the system from the user’s perspective. So, use cases are the functionality that the system provides. Actors are the Administrator and User of a system.

The use case description defines what happens in the system when the use cases performed. It corresponds to a sequence of transactions performed by the system, which yields a measurable result of value to a particular actor. Use case is a narrative documentation that describes the sequence of events of an actor. Sequence diagrams in UML, indicate how events cause transitions from object to object. They are used to show the flow of functionality through a use case. Actors and objects are shown at the top of the diagram. Each arrow represents a message passed between actor and object or object and object to perform the needed functionality. It depicts the objects and classes involved in the scenario and the sequence of messages exchanged between the objects needed to carry out functionality of scenario.

Collaboration diagrams show object interactions organized around the objects and their links to each other. Quality assurance engineer and system architects look at these to see the distribution of processing between objects.