Download for free : STUDY OF UML

Download for free : STUDY OF UML

Aim

General study of UML

Description

The heart of object-oriented problem solving is the construction of a model. The model abstracts the essential details of the underlying problem from its usually complicated real world. Several modeling tools are wrapped under the heading of the UML, which stands for Unified Modeling Language. The purpose of this course is to present important highlights of the UML.

At the center of the UML are its nine kinds of modeling diagrams, which we describe here.

v Use case diagrams

v Class diagrams

v Object diagrams

v Sequence diagrams

v Collaboration diagrams

v State chart diagrams

v Activity diagrams

v Component diagrams

v Deployment diagrams

The UML is applicable to object-oriented problem solving. Anyone interested in learning UML must be familiar with the underlying tenet of object-oriented problem solving -- it all begins with the construction of a model. A model is an abstraction of the underlying problem. The domain is the actual world from which the problem comes. Models consist of objects that interact by sending each other messages. Think of an object as "alive." Objects have things they know (attributes) and things they can do (behaviors or operations). The values of an object's attributes determine its state.

Classes are the "blueprints" for objects. A class wraps attributes (data) and behaviors (methods or functions) into a single distinct entity. Objects are instances of classes.

An Introduction To UML Diagram

The Unified Modeling Language is a language for specifying, constructing, visualizing, and documenting the artifacts of a software-intensive system. Analogous to the use of architectural blueprints in the construction industry, UML provides a common language for describing software models, and it can be used in conjunction with a wide range of software lifecycles and development processes.

1. Use Case Diagram

Use Case diagrams identify the functionality provided by the system (use cases), the users who interact with the system (actors), and the association between the users and the functionality. Use Cases are used in the Analysis phase of software development to articulate the high-level requirements of the system. The primary goals of Use Case diagrams include:

v Providing a high-level view of what the system does

v Identifying the users ("actors") of the system

v Determining areas needing human-computer interfaces.

Graphical Notation

The basic components of Use Case diagrams are the Actor, the Use Case, and the Association.

Actor

An Actor, as mentioned, is a user of the system, and is depicted using a stick figure. The role of the user is written beneath the icon. Actors are not limited to humans. If a system communicates with another application, and expects input or delivers output, then that application can also be considered an actor.

Use Case

A Use Case is functionality provided by the system, typically described as verb + object (e.g. Register Car, Delete User). Use Cases are depicted with an ellipse. The name of the use case is written within the ellipse.

Association

Associations are used to link Actors with Use Cases, and indicate that an Actor participates in the Use Case in some form. Associations are depicted by a line connecting the Actor and the Use Case.

The following image shows how these three basic elements work together to form a use case diagram.

Use case diagrams describe what a system does from the standpoint of an external observer. The emphasis is on what a system does rather than how.

Use case diagrams are helpful in three areas.

Determining features (requirements). New use cases often generate new requirements as the system is analyzed and the design takes shape.
Communicating with clients. Their notational simplicity makes use case diagrams a good way for developers to communicate with clients.
Generating test cases. The collection of scenarios for a use case may suggest a suite of test cases for those scenarios.

2. Sequence Diagram

Sequence diagrams document the interactions between classes to achieve a result, such as a use case. Because UML is designed for object-oriented programming, these communications between classes are known as messages. The Sequence diagram lists objects horizontally, and time vertically, and models these messages over time.

Notation

In a Sequence diagram, classes and actors are listed as columns, with vertical lifelines indicating the lifetime of the object over time.

Object

Objects are instances of classes, and are arranged horizontally. The pictorial representation for an Object is a class (a rectangle) with the name prefixed by the object name (optional) and a semi-colon.