The design and implementation of software is a complex process that requires the expertise of many different disciplines. System developers, software engineers, designers, architects, and other professionals must communicate and collaborate effectively to create software that is lasting. The Unified Modeling Language (or UML) is an effective tool that allows communication between the different disciplines to ensure there is no misunderstanding and everyone is on the same page.
What is UML?
UML is a graphical language that models the design of software systems. You can use UML diagrams to visualize a software system's different components, relationships, and interactions. This can help understand the system, communicate with other team members about the system, and documenting the system for future reference.
A good UML diagram can effectively and concisely communicate design ideas, especially when you do not want to include all the details. In other words, good UML diagrams provide a high level of abstraction for software systems that facilitates discussions about designs. This is something that textual programming languages don't currently offer.
UML is a language with both syntax and semantics. Syntax refers to the rules of the arrangement of UML elements, and semantics refers to the meaning of those elements. When you model a concept, you need to follow the rules of syntax so that your model is understandable to others. The semantics of UML tells you what the model means, such as the relationships and interactions between the elements.
UML sketches can be used in the early stages of software development to capture ideas about parts of the system when the requirements are not yet fully understood. When the requirements are well understood in the later stages, you can use UML to make a detailed design blueprint of the system. This is called forward engineering, where the UML model is created before the implementation of the system. The UML model is made from an existing software system in reverse engineering.
Here are the main roles of UML in the software development process:
- Identify potential problems with the system early in the development process.
- Provide a standard way to communicate design solutions.
- Create documentation that describes the system and its behavior.
How was UML created?
The UML appeared in response to the proliferation of different object-oriented modeling languages in the early 1990s. These languages had different notations and semantics. It was difficult for the different disciplines involved in the software development process to communicate with each other and share their designs and ideas.
The three main authors of the UML were Grady Booch, James Rumbaugh, and Ivar Jacobson. They were already well-known for their work on object-oriented analysis and design, and they had developed their own object modeling languages.
In 1994, Rumbaugh joined Booch at Rational Software Corporation. They joined forces to create the Booch/Rumbaugh Unified Method. This method combined their two existing methods—Booch's Object-Oriented Analysis and Design (OOAD) and Rumbaugh's Object Modeling Technique (OMT). This was the first step towards the creation of the UML.
In 1995, Rational acquired Objectory—a company founded by Ivar Jacobson. This was how Ivar Jacobson joined Rational Software Corporation, and the scope of the UML project was expanded to incorporate Jacobson's Object-Oriented Software Engineering (OOSE) method. The first version of UML (UML 0.8) came in the same year.
Booch, Rumbaugh, and Jacobson formed a UML consortium in 1996 to create and propose a comprehensive UML specification to the Object Management Group (OMG) for standardization. Numerous organizations and authors specializing in Object-Oriented modeling joined this consortium to aid in developing the full UML specification—UML 1.0. The OMG adopted UML as a standard in 1997.
Components and elements in UML
In UML, a component is a modular part of a system that encapsulates its implementation. A component can consist of other components, classes, or interfaces.
Here are some examples of UML components:
- Class: A class is a blueprint for creating objects. It defines the properties and behaviors of objects.
- Object: An object is an instance of a class. It has the properties and behaviors defined by the class.
- Package: A package is a container for grouping related model elements.
- Use case: A use case describes the interactions between the system and its users.
- Association: An association shows that two model elements are related.
An element is a general term for any UML model element, including components, classes, interfaces, use cases, and so on. Elements are the building blocks of UML models. They represent the different aspects of a system. The main difference between components and elements is that components are units of implementations, while elements are abstract representations of things in the system. You can deploy and reuse components, whereas elements only serve to model the system.
Types of UML diagrams
Structural diagrams show the static aspects of a system, such as its classes, objects, interfaces, and components. They depict the architecture of the system and the relationship between its different parts.
The 7 types of structural diagrams include:
- Class diagram
- Object diagram
- Package diagram
- Components diagram
- Deployment diagram
- Composite structure diagram
- Profile diagram
Behavioral diagrams show the dynamic aspects of a system, such as its interactions, activities, and states. They represent how the system behaves and how its different parts interact with each other.
The 6 types of behavioral diagrams include:
- Activity diagram
- Sequence diagram
- Use case diagram
- State machine diagram
- Communication diagram
- Timing diagram
You can use the different types of UML diagrams together to create a comprehensive and accurate representation of a system. The specific diagrams that are used will depend on the needs of the project.
The class diagram
A class is the basic unit of abstraction in object-oriented programming. It describes a set of objects that share the same attributes, operations, and relationships. This means that all objects of a class have the same properties, can perform the same tasks, and are related to each other in the same way.
The following diagram shows the association between the Student and Course classes:
The classes are represented by rectangular boxes divided into compartments. The first compartment shows the name of the class: Student and Course. The second lists the class attributes—for example, studentID for the Student class. The third describes the class operations—for example, addStudent method in the Course class. There is an optional fourth component that lists the class responsibilities at the bottom of the class diagram.
The activity diagram
Activity diagrams are graphical representations that model workflows consisting of stepwise activities and actions within a system. They support depicting choices, iterations, and concurrency in the process. Activity diagrams model the dynamic aspects of a system, illustrating how activities and actions are organized, sequenced, and interrelated.
Here is an example activity diagram with all its components:
The sequence diagram
A sequence diagram shows the chronological order of interactions between objects in a system. It is a visual representation of how different objects collaborate to achieve specific functionality. Sequence diagrams are excellent at showing which objects communicate with which other objects and what messages trigger those communications. They are not intended to show complex procedural logic, but you can use them to understand the flow of control in a system and identify potential problems.
Here is a sequence diagram that depicts the interactions between the :Client and server:Server objects:
In our example, the :Client initiates the interaction by sending a message to the server to authorize the unnamed user. The server processes the request from the client and messages back to the client with the authorization result: passID. This is a synchronous message because the user cannot continue with its own processing until it has received the response from the server. The server and client also interact asynchronously. In this case, the sender does not wait for a response from the receiver to continue with its own processing.
Conclusion
In summary:
- UML bridges interdisciplinary gaps, aiding effective collaboration in software design.
- UML's graphical language visualizes system components, interactions, and relationships.
- High-level UML diagrams provide clarity without overwhelming details.
- Syntax and semantics ensure standardized communication and interpretation of models.
- UML serves early idea capture, detailed blueprint design, reverse engineering, and code generation.
- UML is used to model both the static and dynamic aspects of a system.
UML remains an indispensable tool for seamless communication, efficient design, and enduring software solutions. Online resources like yEd–Graph Editor, draw.io, creately, and Lucidchart can help you get started with using UML.