Unified Modeling Language..

A model is a simplified representation of reality, simplified because reality is too complex or large and much of the complexity actually is irrelevant to the problem, being described or solved.

The Unified Modeling Language was developed by Booch, Jacobson and Rumbaugh. The UML encompasses the unification of their modeling notations.

The UML Class diagram is the main static structure analysis diagram for the system. It represents the class structure of a system with relationships between Classes and Inheritance Structure. The class diagram is developed through Use Case, Sequence and Collaboration diagrams.

The Use Case diagram captures information on how the system or business works or how you wish it to work. It is a scenario – building approach in which you model the processes of the system. It is an excellent way to lead into Object- Oriented analysis of the system.

In the UML Sequence diagram is for dynamic modeling, where objects are represented by vertical lines and messages passed back and forth between the objects are modeled by horizontal vectors between the objects.

The UML Collaboration diagram is an alternative view of the sequence diagram, showing in a scenario how objects interrelate with one another.

State chart diagrams, another form of dynamic modeling, focus on the events occurring within a single object as it responds to messages; an activity diagram is used to model an entire business process. Thus, an activity model represents several different classes.

Implementation diagrams show the implementation phase of systems development, such as the source code and run time implementation structures. The two types of implementation diagrams, which show the structure of the code itself, and deployment diagrams, which show the structure of the run time system.

Stereotypes represent a built – in extensibility mechanism of the UML. User – Defined extensions of the UML are enabled through the use of stereotypes and constraints.

UML graphical notations can be used not only to describe the system’s components but also to describe a model itself, this is known as a Meta – Model. It is a model of Modeling Elements. The purpose of the UML Meta – Model is to provide a single, common and definitive statement of the syntax and semantics of the elements of the UML.

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Object Oriented Methodologies

At Current trends in Object Oriented Methodologies, sometimes known as Second Generation Object Oriented Methods, which have been toward combining the best aspects of today’s most popular methods.

Each method has its strengths.

Ø Rumbaugh et al. have a strong method for producing object models sometimes it is referred to ad Domain Object Models.

Ø Jacobson et al. have a strong method for producing User – Driven requirement and Object – Oriented Analysis Models.

Ø Booch has a strong method for producing detailed Object – Oriented Design Models.

Each method has a weakness, too. While Rumbaugh et al’s OMT has strong methods for modeling the problem domain; OMT models cannot fully express the requirements. Jacobson et al. deemphasize object modeling and although they cover a fairly wide range of the life cycle, they do not treat object – oriented design to the same level as Booch, who focuses almost entirely on design, not analysis.

Booch and Rumbaugh et al. are object centered in their approaches and focus more on figuring out what are the objects of a system, how are they related, and how do they collaborate with each other. Jacobson et al. are more centered, in that everything in their approach derives from use case or usage scenarios.

The Main idea behind a pattern is the documentation to help categorize, communicate about, and locate solutions to recurring problems. Frameworks are a way of delivering application development patterns to support best practice sharing during application development. A single framework typically encompasses several design patterns. In fact, a framework can be viewed as the implementation of a system of design patterns. Writing good patterns is very difficult, since it should not only provide facts but also tell a story that captures the experience the pattern is trying to convey.

The Unified Approach – UA is an attempt to combine the best practices, processes and guidelines along with UML notations and diagrams for better understanding Object – Oriented concepts and Object – Oriented System Development. The UA consists of the following processes:

Ø Use case Driven Development

Ø Object – Oriented Analysis

Ø Object – Oriented Design

Ø Incremental Development and Prototyping

Ø Continuous Testing

Furthermore, it utilizes the methods and technologies such as Unified Modeling Language, Layered Approach and promotes respository for all phases of Software Development.

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Object Oriented System Development Life Cycle

The essence of the Software Process i.e. Analysis, Design, Implementation, Testing and Refinement is the transformation of users' needs through the application domain into a software solution that is executed in the implementation domain. The concept of the Use Case or a set of scenarios can be valuable tool for understanding the User's need. The emphasis on the analysis and design aspects of the software life cycle is intended to promote building high quality software that is Meeting the specifications and being adaptable for change.

High Quality Software provides users with an application that meets their needs and expectations. Four quality measures have been described:

Ø  Correspondence

          Correspondence measures How well the delivered system corresponds to  

          the needs of the problem.

Ø Correctness

          Correctness determines whether or not the system correctly computes

the results based on the rules created during the system analysis and design, measuring the consistency of product requirements with respect to the design specification.

Ø Verification

Verification is the task of determining correctness i.e. “Am I Building the Product Right.?”

Ø Validation

Validation is the task of predicting correctness i.e. “Am I Building the Right Product.?”

Object Oriented Design requires more rigor up front to do things right. You need to spend more time gathering requirements, developing a requirements model and an analysis model, and then turning them into the design model. Now, you can develop code quickly – you have a recipe for doing it. Object Oriented System Development Consists of three Macro processes:

Ø Object Oriented Analysis requires building a use - case model and interaction diagrams to identify User’s needs and the system’s classes and their responsibility, then validating and testing the models, documenting each step along the way.

Ø Object Oriented Design centers on establishing design classes and their protocol; building class diagrams, user interfaces and prototypes; testing satisfaction and usability based on usage and usecases.

The use – case concept can be employed through most of the activities of software development. Furthermore, by following Jacobson’s lifecycle model, one can produce designs that are traceable across requirements, analysis, design, implementation and testing.

Component Based Development – CBD is an industrialized approach to software development. Software components are functional units, or building blocks offering a collection of reusable services. A CBD developers can assemble Components to Construct a complete software components themselves may be constructed from other components and so on down to the level of prebuilt components or old fashioned code written in a language such as C, assembler or COBOL. The Object Oriented Concept addresses analysis, design and programming; whereas component – based development is concerned with the implementation and system integration aspects of software development.

The rapid application development – RAD approach to system development rapidly develops software to quickly and incrementally implement the design by using tools such as CASE.

Reusability is a major benefit of Object Oriented System Development. It is also the most difficult promise to deliver. To develop reusable objects, you must spend time up front to design reusability in the objects.

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Object Basics...

The goal of Object-Oriented Programming is to make development easier, quicker and more natural by raising the level of abstraction to the point where applications can be implemented in the same terms in which they are described by the application domain. The main thrust of object-oriented programming is to provide the user with a set of objects that closely reflects the underlying application. The user who needs to develop a financial application could develop it in a financial language with considerably less difficulty. Object-Oriented programming allows the base concepts of the languages to be entended to include ideas closer to those of its application. You can define a new datatype (object) in terms of an existing data type until it appears that the languages directly supports the primitives of the application. The real advantage of using the object-oriented approach is that you can build on what you already have.

Object-Oriented Software Development is a significant departure from the traditional structured approach. The main advantage of an object-oriented approach is the ability to reuse code and develop more maintainable systems in a shorter amount of time. Additionally, object –oriented systems are better designed, more resilient to change, and more reliable, Since they are built from completely tested and debugged classes.

Rather than treat and procedures separately, object-oriented systems link both closely into objects. Events occur when objects respond to messages. The objects themselves determine the response to the messages, allowing the same message to be sent too many objects.

Each object is an instance of a class. Classes are organized hierarchically in a class tree, and subclasses inherit the behavior of their Superclasses. Good Object-Oriented Programming user encapsulation and polymorphism, which, when used in the definition of classes, result in completely reusable abstract data classes. Objects have a lifetime. They are explicitly created and can exist for a period of time that traditionally, has been the duration of the process for which they were created. A file or a database can provide support for objects have a longer lifeline-longer than the duration of the process for which they were created.

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Intro to Object Oriented Analysis and Design

In an Object - Oriented environment, software is a collection of discrete objects that encapsulate their data and the functionality to model real – world “Objects”. Once objects are defined, you can take it for granted that they will perform their desired functions and so seal them off in your mind like black boxes. Your attention as a programmer shifts to what they do rather than how they do it. The Object Oriented Life Cycle encourages a view of the world as a system of co- operative and collaborating agents.

An Object Orientation produces systems that are easier to evolve, more flexible, more robust and more reusable than a top – down structure approach.

An Object Orientation

Ø  Allows working at a higher level of abstraction

Ø  Provides a seamless transition among different phases of s0ftware development.

Ø  Encourages good development practices.

Ø  Promotes reusability.

The Unified Approach (UA) is the methodology for software development proposed and is based on the Booch, Rumbaugh and Jacobson Methodologies. The UA consists of the following concepts

Ø  Use – Case driven Development

Ø  Utilizing the unified modeling language for modeling.

Ø  Object Oriented Analysis( Utilizing Use Cases and Object Modeling).

Ø  Object Oriented Design

Ø  Respositories of reusable classes and maximum reuse.

Ø  The Layered approach.

Ø  Incremental Development and prototyping

Ø  Continuous testing

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