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Week 4

Object Oriented Methodology Life Cycle Model  

We live in a world of objects. These objects exist in nature, in man-made entities, in business, and in the products that we use. They can be categorized, described, organized, combined, manipulated and created. Therefore, an object-oriented view has come into picture for creation of computer software. An object-oriented approach to the development of software was proposed in late 1960s.  

Object-Oriented development requires that object-oriented techniques be used during the analysis, and implementation of the system. This methodology asks the analyst to determine what the objects of the system are, how they behave over time or in response to events, and what responsibilities and relationships an object has to other objects. Object-oriented analysis has the analyst look at all the objects in a system, their commonalties, difference, and how the system needs to manipulate the objects.

Object Oriented Process

The Object Oriented Methodology of Building Systems takes the objects as the basis. For this, first the system to be developed is observed and analyzed and the requirements are defined as in any other method of system development. Once this is done, the objects in the required system are identified. For example in case of a Banking System, a customer is an object, a chequebook is an object, and even an account is an object.

In simple terms, Object Modeling is based on identifying the objects in a system and their interrelationships. Once this is done, the coding of the system is done. Object Modeling is somewhat similar to the traditional approach of system designing, in that it also follows a sequential process of system designing but with a different approach. The basic steps of system designing using Object Modeling may be listed as:

·                  System Analysis

·                  System Design

·                  Object Design

·                  Implementation

System Analysis

As in any other system development model, system analysis is the first phase of development in case of Object Modeling too. In this phase, the developer interacts with the user of the system to find out the user requirements and analyses the system to understand the functioning.

Based on this system study, the analyst prepares a model of the desired system. This model is purely based on what the system is required to do. At this stage the implementation details are not taken care of. Only the model of the system is prepared based on the idea that the system is made up of a set of interacting objects. The important elements of the system are emphasized.

System Design

System Design is the next development stage where the overall architecture of the desired system is decided. The system is organized as a set of sub systems interacting with each other. While designing the system as a set of interacting subsystems, the analyst takes care of specifications as observed in system analysis as well as what is required out of the new system by the end user.

As the basic philosophy of Object-Oriented method of system analysis is to perceive the system as a set of interacting objects, a bigger system may also be seen as a set of interacting smaller subsystems that in turn are composed of a set of interacting objects. While designing the system, the stress lies on the objects comprising the system and not on the processes being carried out in the system as in the case of traditional Waterfall Model where the processes form the important part of the system.

Object Design

In this phase, the details of the system analysis and system design are implemented. The Objects identified in the system design phase are designed. Here the implementation of these objects is decided as the data structures get defined and also the interrelationships between the objects are defined.

Let us here deviate slightly from the design process and understand first a few important terms used in the Object-Oriented Modeling.

As already discussed, Object Oriented Philosophy is very much similar to real world and hence is gaining popularity as the systems here are seen as a set of interacting objects as in the real world. To implement this concept, the process-based structural programming is not used; instead objects are created using data structures. Just as every programming language provides various data types and various variables of that type can be created, similarly, in case of objects certain data types are predefined.

For example, we can define a data type called pen and then create and use several objects of this data type. This concept is known as creating a class.

Class: A class is a collection of similar objects. It is a template where certain basic characteristics of a set of objects are defined. The class defines the basic attributes and the operations of the objects of that type. Defining a class does not define any object, but it only creates a template. For objects to be actually created instances of the class are created as per the requirement of the case.

Abstraction: Classes are built on the basis of abstraction, where a set of similar objects are observed and their common characteristics are listed. Of all these, the characteristics of concern to the system under observation are picked up and the class definition is made. The attributes of no concern to the system are left out. This is known as abstraction.

The abstraction of an object varies according to its application. For instance, while defining a pen class for a stationery shop, the attributes of concern might be the pen color, ink color, pen type etc., whereas a pen class for a manufacturing firm would be containing the other dimensions of the pen like its diameter, its shape and size etc.

Inheritance: Inheritance is another important concept in this regard. This concept is used to apply the idea of reusability of the objects. A new type of class can be defined using a similar existing class with a few new features. For instance, a class vehicle can be defined with the basic functionality of any vehicle and a new class called car can be derived out of it with a few modifications. This would save the developers time and effort as the classes already existing are reused without much change.

Coming back to our development process, in the Object Designing phase of the Development process, the designer decides onto the classes in the system based on these concepts. The designer also decides on whether the classes need to be created from scratch or any existing classes can be used as it is or new classes can be inherited from them.

Implementation

During this phase, the class objects and the interrelationships of these classes are translated and actually coded using the programming language decided upon. The databases are made and the complete system is given a functional shape.

The complete OO methodology revolves around the objects identified in the system. When observed closely, every object exhibits some characteristics and behavior. The objects recognize and respond to certain events. For example, considering a Window on the screen as an object, the size of the window gets changed when resize button of the window is clicked.

Here the clicking of the button is an event to which the window responds by changing its state from the old size to the new size. While developing systems based on this approach, the analyst makes use of certain models to analyze and depict these objects. The methodology supports and uses three basic Models:

·                  Object Model - This model describes the objects in a system and their interrelationships. This model observes all the objects as static and does not pay any attention to their dynamic nature.

·                  Dynamic Model - This model depicts the dynamic aspects of the system. It portrays the changes occurring in the states of various objects with the events that might occur in the system.

·                  Functional Model - This model basically describes the data transformations of the system. This describes the flow of data and the changes that occur to the data throughout the system.

While the Object Model is most important of all as it describes the basic element of the system, the objects, all the three models together describe the complete functional system.

As compared to the conventional system development techniques, OO modeling provides many benefits. Among other benefits, there are all the benefits of using the Object Orientation. Some of these are:

·                  Reusability - The classes once defined can easily be used by other applications. This is achieved by defining classes and putting them into a library of classes where all the classes are maintained for future use. Whenever a new class is needed the programmer looks into the library of classes and if it is available, it can be picked up directly from there.

·                  Inheritance - The concept of inheritance helps the programmer use the existing code in another way, where making small additions to the existing classes can quickly create new classes.

·                  Programmer has to spend less time and effort and can concentrate on other aspects of the system due to the reusability feature of the methodology.

·                  Data Hiding - Encapsulation is a technique that allows the programmer to hide the internal functioning of the objects from the users of the objects. Encapsulation separates the internal functioning of the object from the external functioning thus providing the user flexibility to change the external behaviour of the object making the programmer code safe against the changes made by the user.

·                  The systems designed using this approach are closer to the real world as the real world functioning of the system is directly mapped into the system designed using this approach.

Advantages of Object Oriented Methodology 

·                  Object Oriented Methodology closely represents the problem domain. Because of this, it is easier to produce and understand designs.

·                  The objects in the system are immune to requirement changes. Therefore, allows changes more easily.

·                  Object Oriented Methodology designs encourage more re-use. New applications can use the existing modules, thereby reduces the development cost and cycle time.

·                  Object Oriented Methodology approach is more natural. It provides nice structures for thinking and abstracting and leads to modular design.

Dynamic System Development Method (DSDM) 

Dynamic System Development Method is another approach to system development, which, as the name suggests, develops the system dynamically. This methodology is independent of tools, in that it can be used with both structured analysis and design approach or object-oriented approach.  

The Dynamic System Development Method (DSDM) is dynamic as it is a Rapid Application Development method that uses incremental prototyping. This method is particularly useful for the systems to be developed in short time span and where the requirements cannot be frozen at the start of the application building. Whatever requirements are known at a time, design for them is prepared and design is developed and incorporated into system. In Dynamic System Development Method (DSDM), analysis, design and development phase can overlap. Like at one time some people will be working on some new requirements while some will be developing something for the system. In Dynamic System Development Method (DSDM), requirements evolve with time.

Dynamic System Development Method (DSDM) has a five-phase life cycle as given the following figure

Feasibility study

In this phase the problem is defined and the technical feasibility of the desired application is verified. Apart from these routine tasks, it is also checked whether the application is suitable for Rapid Application Development (RAD) approach or not. Only if the RAD is found as a justified approach for the desired system, the development continues.

Business study 

In this phase the overall business study of the desired system is done. The business requirements are specified at a high level and the information requirements out of the system are identified. Once this is done, the basic architectural framework of the desired system is prepared.

The systems designed using Rapid Application Development (RAD) should be highly maintainable, as they are based on the incremental development process. The maintainability level of the system is also identified here so as to set the standards for quality control activities throughout the development process.

Functional Model Iteration 

This is one of the two iterative phases of the life cycle. The main focus in this phase is on building the prototype iteratively and getting it reviewed from the users to bring out the requirements of the desired system. The prototype is improved through demonstration to the user, taking the feedback and incorporating the changes. This cycle is repeated generally twice or thrice until a part of functional model is agreed upon. The end product of this phase is a functional model consisting of analysis model and some software components containing the major functionality

Design and Build Iteration 

This phase stresses upon ensuring that the prototypes are satisfactorily and properly engineered to suit their operational environment. The software components designed during the functional modeling are further refined till they achieve a satisfactory standard. The product of this phase is a tested system ready for implementation.

There is no clear line between these two phases and there may be cases where while some component has flown from the functional modeling to the design and build modeling while the other component has not yet been started. The two phases, as a result, may simultaneously continue.

Implementation 

Implementation is the last and final development stage in this methodology. In this phase the users are trained and the system is actually put into the operational environment. At the end of this phase, there are four possibilities, as depicted by figure :

·                  Everything was delivered as per the user demand, so no further development required.

·                  A new functional area was discovered, so return to business study phase and repeat the whole process

·                  A less essential part of the project was missed out due to time constraint and so development returns to the functional model iteration.

·                  Some non-functional requirement was not satisfied, so development returns to the design and build iterations phase.

Dynamic System Development Method (DSDM) assumes that all previous steps may be revisited as part of its iterative approach. Therefore, the current step need be completed only enough to move to the next step, since it can be finished in a later iteration. This premise is that the business requirements will probably change anyway as understanding increases, so any further work would have been wasted.

According to this approach, the time is taken as a constraint i.e. the time is fixed, resources are fixed while the requirements are allowed to change. This does not follow the fundamental assumption of making a perfect system the first time, but provides a usable and useful 80% of the desired system in 20% of the total development time. This approach has proved to be very useful under time constraints and varying requirements.

DSDM Model Limitations 

·        It is a relatively new model. It is not very common. So it is difficult to understand.

DSDM Model Advantages

·                  Active user participation throughout the life of the project and iterative nature of development improves quality of the product.

·                  DSDM ensures rapid deliveries.

·                  Both of the above factors result in reduced project costs

Preliminary Analysis 

The main objectives of preliminary analysis is to identify the customer's needs, evaluate system concept for feasibility, perform economic and technical analysis, perform cost benefit analysis and create system definition that forms the foundation for all subsequent engineering works. There should be enough expertise available for hardware and software for doing analysis.

While performing analysis, the following questions arise.

·                  How much time should be spent on it?
As such, there are no rules or formulas available to decide on this. However, size, complexity, application field, end-use, contractual obligation are few parameters on which it should be decided.

·                  Other major question that arises is who should do it.
Well an experienced well-trained analyst should do it. For large project, there can be an analysis team.

After the preliminary analysis, the analyst should report the findings to management, with recommendations outlining the acceptance or rejection of the proposal.