UML - Overview
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.
OMG is continuously putting effort to make a truly industry standard.
UML stands for Unified Modeling Language.
UML is different from the other common programming languages like C++, Java, COBOL etc.
UML is a pictorial language used to make software blue prints.
So UML can be described as a general purpose visual modeling language to visualize, specify, construct and document software system. Although UML is generally used to model software systems but it is not limited within this boundary. It is also used to model non software systems as well like process flow in a manufacturing unit etc.
UML is not a programming language but tools can be used to generate code in various languages using UML diagrams. UML has a direct relation with object oriented analysis and design. After some standardization UML is become an OMG (Object Management Group) standard.
Goals of UML:
A picture is worth a thousand words, this absolutely fits while discussing about UML. Object oriented concepts were introduced much earlier than UML. So at that time there were no standard methodologies to organize and consolidate the object oriented development. At that point of time UML came into picture.
There are a number of goals for developing UML but the most important is to define some general purpose modeling language which all modelers can use and also it needs to be made simple to understand and use.
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.
A conceptual model of UML:
To understand conceptual model of UML first we need to clarify What is a conceptual model? and Why a conceptual model is at all required?
A conceptual model can be defined as a model which is made of concepts and their relationships.
A conceptual model is the first step before drawing a UML diagram. It helps to understand the entities in the real world and how they interact with each other.
As UML describes the real time systems it is very important to make a conceptual model and then proceed gradually. Conceptual model of UML can be mastered by learning the following three major elements:
- UML building blocks
- Rules to connect the building blocks
- Common mechanisms of UML
Object oriented concepts:
UML can be described as the successor of object oriented analysis and design.
An object contains both data and methods that control the data. The data represents the state of the object. A class describes an object and they also form hierarchy to model real world system. The hierarchy is represented as inheritance and the classes can also be associated in different manners as per the requirement.
The objects are the real world entities that exist around us and the basic concepts like abstraction, encapsulation, inheritance, polymorphism all can be represented using UML.
So UML is powerful enough to represent all the concepts exists in object oriented analysis and design. UML diagrams are representation of object oriented concepts only. So before learning UML, it becomes important to understand OO concepts in details.
Following are some fundamental concepts of object oriented world:
Objects: Objects represent an entity and the basic building block.
Class: Class is the blue print of an object.
Abstraction: Abstraction represents the behavior of an real world entity.
Encapsulation: Encapsulation is the mechanism of binding the data together and hiding them from outside world.
Inheritance: Inheritance is the mechanism of making new classes from existing one.
Polymorphism: It defines the mechanism to exists in different forms.
OO Analysis and Design
Object Oriented analysis can be defined as investigation and to be more specific it is the investigation of objects. Design means collaboration of identified objects.
So it is important to understand the OO analysis and design concepts. Now the most important purpose of OO analysis is to identify objects of a system to be designed. This analysis is also done for an existing system. Now an efficient analysis is only possible when we are able to start thinking in a way where objects can be identified. After identifying the objects their relationships are identified and finally the design is produced.
So the purpose of OO analysis and design can described as:
Identifying the objects of a system.
Identify their relationships.
Make a design which can be converted to executables using OO languages.
There are three basic steps where the OO concepts are applied and implemented. The steps can be defined as
OO Analysis --> OO Design --> OO implementation using OO languages
Now the above three points can be described in details:
During object oriented analysis the most important purpose is to identify objects and describing them in a proper way. If these objects are identified efficiently then the next job of design is easy. The objects should be identified with responsibilities. Responsibilities are the functions performed by the object. Each and every object has some type of responsibilities to be performed. When these responsibilities are collaborated the purpose of the system is fulfilled.
The second phase is object oriented design. During this phase emphasis is given upon the requirements and their fulfilment. In this stage the objects are collaborated according to their intended association. After the association is complete the design is also complete.
The third phase is object oriented implementation. In this phase the design is implemented using object oriented languages like Java, C++ etc.
Role of UML in OO design:
UML is a modeling language used to model software and non software systems. Although UML is used for non software systems the emphasis is on modeling object oriented software applications. Most of the UML diagrams discussed so far are used to model different aspects like static, dynamic etc. Now what ever be the aspect the artifacts are nothing but objects.
If we look into class diagram, object diagram, collaboration diagram, interaction diagrams all would basically be designed based on the objects.
So the relation between OO design and UML is very important to understand. The OO design is transformed into UML diagrams according to the requirement. Before understanding the UML in details the OO concepts should be learned properly. Once the OO analysis and design is done the next step is very easy. The input from the OO analysis and design is the input to the UML diagrams.