We are in Public Review!

Welcome to the BTABoK 3.0 (formerly known as the ITABoK), the next release of the BTABoK focused equally on business and technology for architects. We are taking feedback for the full release and are now entering the review cycle so we welcome your comments. The previous published version can always be accessed at ITABoK version 2.0

Patterns

“All well-structured object-oriented architectures are full of patterns. Indeed, one of the ways that I measure the quality of an object-oriented system is to judge whether or not its developers have paid careful attention to the common collaborations among its objects.”

Grady Booch, Design Patterns: Elements of Reusable Object-Oriented Software

Design Patterns

Developers must design clean, clearly designed code to avoid bug creep into the system, and avoid complexity. Designing a system is not easy.

However, it is not required to solve all problems “from scratch”. It is preferable to learn from and deploy the lessons from the captured experiences of other designers.

Design Patterns are reusable solutions to common problems in software system design.

History of Design Patterns

Christopher Alexander and his colleagues were the first to discuss patterns in the context of building and construction (The Timeless Way of Building, 1979; A Pattern Language—Towns, Buildings, Construction, 1977). They had 253 patterns.

Over time, it has been observed that there are many similarities between software design and architectural design (as in the context of building construction).

This observation was used by different software design experts. The most well-known technical” work on this has been by Erich Gamma, John Vlissides, Ralph Johnson, and Richard Helm in “Design Patterns: Elements of Reusable Object-Oriented Software”, published in 1994. The four authors (famously known as the Gang of Four) applied the concepts of patterns to software design.

Over time, the library of patterns has grown. There are patterns spanning a range of topics in the software domain, like Cloud patterns, Microservice patterns, Enterprise systems patterns and general software design patterns. 

How can Design Patterns Help?

Design patterns help to speed up the development process through the usage of proven and tested building blocks for the context under consideration. They provide a means to address common problems that frequent occur in the design of software development, irrespective of the category.

Reusability

The fundamental principle here is to avoid reinventing the wheel.

For example, consider the MVC (Model-View-Controller) pattern that was traditionally used in the design of desktop user interfaces. It was observed that web-based UIs had similar or related requirements and design principles; it led to the adoption of the MVC pattern in Web-based UI systems as well.

Common Vocabulary

Design patterns provide a common vocabulary for software engineers to communicate, through the usage of well-known and well-understood names for specific software interactions.

For example, when a designer refers to the usage of a singleton in a specific software design, it is immediately obvious to other designers and developers what is required.

Reducing the amount of variability and increasing Cohesion

Once the problem has been studied, designing with patterns will result in a cohesive solution with minimal coupling, built with “pre-fabricated” blocks. There will be fewer parts in the design that cannot be achieved with patterns.

Specifying Design Patterns

The specification of a Design Pattern is usually subjective. However, most specifications usually conform to the basic template below.

TermDescription
NameA short descriptive appellation for the pattern, usually indicative of its purpose.
Functional descriptionA description of what the pattern does.
SynonymsOther names for the pattern
MotivationA description of the problem for which this pattern could be the solution
Usage scenarioWhere this pattern would be applicable
Structure How to construct an implementation based on this pattern
StakeholdersOther entities with whom the construct in question would interact, and how the interaction would take place. The individual responsibilities of all the actors in the given scenario.
Expected BehaviourThe consequences of the usage of the pattern in a given situation

Pattern Types and Catalog

Pattern TypeArchitectural RelevancePatterns
CloudInfrastructure, Software, SolutionCloud Patterns Library
MicroservicesInfrastructure, Software, SolutionMicroservices Patterns Library
Software DesignSoftware, SolutionSoftware Patterns Library (example: Gang of Four