Pattern Page

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A pattern is a judgement, partially abstracted from its context. It may be positive or negative, and may apply across multiple domains.

Purpose. A popular misunderstanding about patterns is that they are merely abstract components – prefabricated chunks of analysis or design that can be instantly assembled into a solution – the engineering equivalent of convenience foods.

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Form. Patterns are often described as solutions in context. But within the software engineering world there has been a strong emphasis on reuse. In order to reuse something, it has to be taken away from its original context – at least to some extent – and generalized so that it can be plugged into a range of contexts.

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Process. A pattern language represents a shared repository of knowledge. This implies a process of disseminating and using this
knowledge. It also implies a process of maintaining and refreshing the knowledge.

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Material. Patterns come out of lived experience.

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Articles, presentations and white papers on patterns

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Purpose of Patterns

veryard projects > patterns > purpose

A popular misunderstanding about patterns is that they are merely abstract components – prefabricated chunks of analysis or design that can be instantly assembled into a solution – the engineering equivalent of convenience foods. Anyone who reads Christopher Alexander’s original work on patterns cannot fail to sense an entirely different passion and purpose for patterns – the need for quality in the finished product – a quality that Alexander calls The Quality Without a Name.

On this view, patterns are not intended to make the engineering process faster or more efficient – or even more reliable. The purpose of patterns is to impart character to an artefact. Pattern languages are intended to help engineers communicate an awareness of the character and quality of design – with one another and with their clients.

Form of Patterns

veryard projects > patterns > form

Patterns are often described as solutions in context. This description can be traced back to Christopher Alexander, sometimes seen as the father of patterns, who is very keen to emphasize the grounded, context-dependent nature of true patterns.

Within the software engineering world, in contrast, there has been a strong emphasis on reuse. In order to reuse something, it has to be taken away from its original context – at least to some extent – and generalized so that it can be plugged into a range of contexts. This means that a pattern has to be partially abstracted from its context.

Good pattern work has always maintained tension between two opposite positions – the immanent and the transcendental – between solutions that are grounded in the specifics of a given situation, and solutions that are timeless and universal. Alexander expresses this tension by insisting that you can use a pattern a million times over, without ever doing it the same way twice. In a manner of speaking, this is repetition without repetition.

A pattern has the structure of a judgement – it involves an appreciation of a situation, leading to an intelligent response or action. This leads me to define a pattern as a judgement partially abstracted from its context.

The business problems addressed in many patterns are sketched rather than fully defined. This makes it quicker to read the pattern and recognize whether it might be relevant to the problem facing you. But it means that the onus remains on you to investigate the problem in detail and work out how to use the pattern in this specific context.

Process of Patterns

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A pattern language represents a shared repository of knowledge. This implies a process of disseminating and using this
knowledge – deploying the pattern language. It also implies a process of maintaining and refreshing the knowledge –
testing the implicit hypotheses and assumptions, polishing the structures, formulating alternatives and improvements, and
perhaps abandoning certain patterns that have outlived their usefulness.

Publishing patterns, either individually or packaged into languages and catalogs, only makes sense if it fits into a cycle of knowledge generation and critical evaluation and evolution. There is an obligation on the author and publisher to release updates and revisions. There is also an obligation on the reader and user of the pattern language, to participate in the improvement cycle, by contributing critical comment and experience – and we hope that the Internet will facilitate such participation.

Material of Patterns

veryard projects > patterns > material

Patterns should come out of lived experience. They communicate something that has worked – and worked repeatedly.

A useful source of business patterns seems to be the management journals. Sloan Management Review and Harvard Business Review publish lots of ideas of business strategy and organizational design that could be expressed as patterns. The best articles show how the same basic idea is applied in different ways to a variety of practical situations, with an evaluation of the various outcomes.

There are some interesting relationships between patterns in different domains - for example between business patterns, and technical distribution patterns. Some of the patterns (such as Federation) are the same in both, albeit with different interpretations and implementations. However, the patterns of managed change often conflict with the principles of distribution. For example, Concentration of Power.

This encourages some pattern authors to create patterns based on metaphor - where something that works in one domain is assumed to work in another domain, without detailed justification.

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