The Agile Modeling (AM) Method

UML Component Diagram: Diagramming Guidelines

Component-based development (CBD) and object-oriented development go hand-in-hand, and it is generally recognized that object technology is the preferred foundation from which to build components. The Unified Modeling Language (UML) includes a component diagram that shows the dependencies among software components, including the classifiers that specify them (for example implementation classes) and the artifacts that implement them; such as source code files, binary code files, executable files, scripts and tables.Component diagrams, along with UML Activity diagrams, are arguably one of the “forgotten” UML diagrams. Few books invest much time discussing them, I suspect the primary reason for this is because most methodologists appear to relegate them to low-level design diagrams for specifying the configuration of your software. UML Deployment diagrams are preferred by most modelers for this task, not only can you define what you intend to deploy you can also indicate where you intend to deploy it with deployment diagrams, and most programmers prefer to use their configuration management system to define configurations. UML Component diagrams become much more useful when used as architectural-level artifacts, perhaps used to model the logical architecture of your technical or business/domain infrastructures.There are guidelines for:

  1. Components
  2. Interfaces
  3. Dependencies and Inheritance

1. Components

As you can see in Figure 1 UML 2.X components are modeled as rectangles with either a visual stereotype in the top left corner or the textual stereotype of <>. Components realize one or more interfaces, modeled using the lollipop notation in Figure 1, and may have dependencies on other components – as you can see the Persistence component has a dependency on the Corporate DB component.

Figure 1. A UML Component 2.x diagram representing the logical architecture of a simple e-commerce system.


  1. Use Descriptive Names for Architectural Components
  2. Use Environment-Specific Naming Conventions for Detailed Design Components
  3. Apply Textual Stereotypes to Components Consistently
  4. Avoid Modeling Data and User Interface Components


2. Interfaces

  1. Prefer Lollipop Notation To Indicate Realization of Interfaces By Components
  2. Prefer the Left-Hand Side of A Component for Interface Lollipops
  3. Show Only Relevant Interfaces


3. Dependencies and Inheritance

Components will have dependencies either on other components or better yet on the interfaces of other components. As you can see in Figure 1 and Figure 2 dependencies are modeled using a dashed line with an open arrowhead.

  1. Model Dependencies From Left To Right
  2. Place Child Components Below Parent Components
  3. Components Should Only Depend on Interfaces
  4. Avoid Modeling Compilation Dependencies

Recommended Reading

Modeling style: Elements of UML 2.0 Style The Elements of UML 2.0 Style describes a collection of standards, conventions, and guidelines for creating effective UML diagrams. They are sound, proven strategies that lead to diagrams that are easier to understand and work with. These conventions exist as a collection of simple, concise guidelines that if applied consistently, represent an important first step in increasing your productivity as a modeler. This book is oriented towards intermediate to advanced UML modelers. Although there are numerous examples throughout the book it would not be a good way to learn the UML (instead, consider The Object Primer). The book is 188 pages long and is conveniently pocket-sized so it’s easy to carry around.
Choose Your WoW! 2nd Edition This book, Choose Your WoW! A Disciplined Agile Approach to Optimizing Your Way of Working (WoW) – Second Edition, is an indispensable guide for agile coaches and practitioners. It overviews key aspects of the Disciplined Agile® (DA™) tool kit. Hundreds of organizations around the world have already benefited from DA, which is the only comprehensive tool kit available for guidance on building high-performance agile teams and optimizing your WoW. As a hybrid of the leading agile, lean, and traditional approaches, DA provides hundreds of strategies to help you make better decisions within your agile teams, balancing self-organization with the realities and constraints of your unique enterprise context.
The Object Primer 3rd Edition: Agile Model Driven Development (AMDD) with UML 2 The Object Primer 3rd Edition: Agile Model Driven Development with UML 2 is an important reference book for agile modelers, describing how to develop 35 types of agile models including all 13 UML 2 diagrams. Furthermore, this book describes the fundamental programming and testing techniques for successful agile solution delivery. The book also shows how to move from your agile models to source code, how to succeed at implementation techniques such as refactoring and test-driven development(TDD). The Object Primer also includes a chapter overviewing the critical database development techniques (database refactoringobject/relational mappinglegacy analysis, and database access coding) from my award-winning Agile Database Techniques book.