Anatomy of a Pattern Language
Parts and links.
A pattern language consists of a cascade or hierarchy of parts,
linked together by patterns which solve generic recurring
problems associated with the parts.
Each pattern has a title and collectively the titles form a language
"In this network, the links between the patterns are almost as much a
part of the language as the patterns themselves."
Christopher Alexander in
The Timeless Way of Building
In a pattern language individual patterns are not isolated.
The structure of the language is composed of the links from
larger patterns to smaller patterns, together creating a
Thus, for a single pattern to work fully, it must not only
be followed through by implementing the smaller patterns
that complete it, it must if at all possible be connected
to certain larger patterns.
The links from larger (predecessor) patterns to smaller (successor)
patterns in this network define the order in which the patterns should
be applied to a design.
This is called the Pattern Language sequence, but the sequence
is not mechanically linear.
Hierarchy of Parts
Parts can be composed with others to make up larger
parts and decomposed into smaller parts, forming a type of
system model called a structural hierarchy
For an example of a hierarchy of parts see our
A hierarchy of parts is not a formal part of a pattern language,
but constructing such a hierarchy is a good way to begin defining
a pattern language, as suggested by Alexander and others in
some early treatises on the Pattern Language.
Many parts are given, especially those of nature, and cannot be
changed by design.
But the existence of some other parts in a design are themselves
patterns, because they help to resolve problematic forces at the
interface of other parts, or they respond to a basic human need.
A pattern is essentially a morphological law, a relationship among
parts within a particular context.
Specifically, a pattern expresses a relationship among parts
that resolves problems that would exist if the relationship
As patterns express these relationships, they are not formulae
or algorithms, but rather loose rules of thumb or heuristics.
Some authors who have adopted the idea of a Pattern Language,
such as some of those for object-oriented programming in software,
have deviated from the format used in
A Pattern Language.
We also note that patterns are similar to documents
often referred to as
or design factors.
Indeed, these documents may evolve into full-fledged patterns.
But without certain critical elements, a collection of patterns
fall short of being a pattern language.
As noted above, linkage between patterns is critical for a set of
patterns to become a
rather than a collection of isolated standalone ideas for design.
In particular, the predecessor
and successor patterns cited at the beginning and end of
each pattern make the patterns hang together as a network
- as a whole.
And each pattern must have successor patterns directly under it,
and successor patterns under those in turn, so that
together all of the problems that might come up are resolved,
thus making the language functionally and morphologically complete.
Here we will stick very close to the anatomy of patterns as
A Pattern Language
by Alexander et al.
However, we will also include some elements that existed in
early incarnations of the Pattern Language, which we feel are
particularly useful in constructing new pattern languages.
We will also include some elements we find useful for managing
a language under development, and for putting patterns on the
World Wide Web.
A Title which is used to refer to the pattern. Titles
are chosen to fit into the natural discourse of discussions
about the design (per linguist Noam Chomsky), hence, a pattern
On the Web it is advisable to repeat this title within the
HTML <title> tag.
A key Visualization which illustrates the pattern.
This may be a photo, diagram, sketch or anything else that
captures the pattern's essence.
Note that this is optional - not all patterns in
A Pattern Language have a key visualization -
but they help with memory and giving people an image that
exemplifies the "goodness" of the pattern.
Parts/Contexts, i.e., a description of one or more parts
and contexts to which the Pattern applies.
A Pattern Language does not include this element in
patterns, but we note that this work publishes the 253 patterns
that Alexander et al deemed the most generic, the most
universal. Many other patterns exist which apply to specific
parts or social, cultural or ecological contexts. For example, the
Center For Environmental Structure itself published other patterns
for a multi-service center, and for housing in Peru.
It is our opinion that citing the parts and contexts in which
the pattern is relevant is useful for finding those applicable
to one's situation, and on-line can be useful in searches.
Keywords to help determine the application of the
This also is not an element of patterns published in
A Pattern Language, but keywords would assist finding
patterns that apply to a specific project, especially on-line.
For patterns on the Web, we recommend also placing the same
keywords inside a META tag for the benefit of search engines.
describe how patterns that apply to larger parts, hence are
implemented before this pattern if possible, relate to this
This is the section in
A Pattern Language that begins with an ellipsis
(. . .) to indicate continuity from the predecessor patterns
that refer to this pattern.
Note that for a given project you may not have the ability to
directly implement predecessor patterns.
For example, in implementing patterns for a house, one likely
has no control over the surrounding urban design.
But one should review predecessor patterns nontheless to see
how implementing this pattern can help complete them.
On the Web make the predecessor pattern titles hyperlinks if they
are also on the Web.
The Problem Summary, or headline states the essence of
the generic problem.
To get at the underlying forces bearing on the problem, the
Problem Summary is often stated as a loosely dependent clause
using conjunctions like if, because,
while, where, unless or when.
The Analysis section contains
information describing the context or circumstances in
which the problem exists, an explication of the functions and
forces involved, and analysis of experiments or other proofs of
The Solution Summary is an imperative statement that
begins with Therefore that describes design action that
would resolve the forces causing the problem.
Successor Patterns tells what patterns next in the
language sequence apply to smaller parts, and are therefore
implemented after this pattern to complete it.
On the Web
make the pattern titles hyperlinks if possible.
A Pattern Language successor patterns are followed by an
ellipsis (. . .) to indicate continuity.
can be personal observations or experiments as well
as bibliographic entries.
performs an administrative function in a team effort,
and if the date is a revision date, it lets the user know
when it has been updated.
In early versions of the pattern language each pattern included
a list of authors together with the statement:
This pattern is tentative. If you have any evidence to
support or refute its current formulation, please send it to the
Center for Environmental Structure (address); we will add your
comments to the next edition.
We feel that such a statement is extremely useful for a pattern
language that is under development.
Return to Pattern Index.
For patterns on the Web this element provides a link to the
master index or table of contents. This provides a navigational
aid, supplementing the network of hyperlinks for predecessor and
In the spirit of "information should be free", we suggest a
copyright notice that gives permission for non-profit academic
use, for example:
© Your Name, 1996. Permission to copy this pattern for
non-profit academic use is granted so long as this copyright
notice is retained. To copy otherwise requires specific
We note that early working versions of
A Pattern Language encouraged copying in order to promote
both the idea of a pattern language, as well as the individual
patterns to help improve the environment.