A personal note on Pattern Language applications in other fields

I have noticed a number of recent adaptations of Christopher Alexander’s ‘Pattern Language’ idea in areas that are quite different from architecture and urban design, [1] were the subject of his first trilogy of Pattern Language books — ‘The Timeless Way of Building’, ‘A Pattern Language’, and ‘The Oregon Experiment’. [2] This is somewhat curious because at the same time, a similar rash of references is occurring about another familiar idea from the same time and place — Horst Rittel’s concept of “Wicked Problems”. [3]

Both Alexander and Rittel were teaching at Berkeley when I was there as a graduate and then postgraduate student, in the late 1960’s and early 1970’s. Both belonged to the ‘design methods’ movement, a group of people who tried to remedy what was widely seen as a lack of research and adaptation of the new ‘space age’ insights in architecture and urban design and planning. They tried to bring ideas and tools from operations research, the emerging computer applications and systems studies to bear on architecture and planning. However, Alexander dramatically disassociated himself from that group, after a first disappointing attempt at devising a computer program to produce architectural designs. [4] He then focused on his ambitious pattern language project. This was seen as a move philosophically opposing the methods and systems efforts — efforts whose early applications in the sociopolitical arena had seen some spectacular failures.

It is interesting to attempt a brief, crude comparison of the reactions by Alexander and Rittel to these experiences.

Rittel’s recognition of the ‘wicked’ nature of not only architectural design problems but especially these large scale social policy problems led him to what he called the ‘second generation’ design methods, facing the significant role of the information needed to deal with these problems — information that is largely ‘distributed’ in the population affected by the problems and proposed solutions, and therefore calls for wide and open participation by the public. He therefore launched the development of ‘issue based information systems’ (IBIS) and ‘argumentative planning information systems’ (APIS) in which that distributed information would be collected and discussed and argued: the “Argumentative Model of Planning”. [5] A model in which resulting decisions are not ‘right’ or ‘wrong’, ‘correct’ or ‘false’, due to the wicked nature of the problems, and the fact that the ‘deontic’ (ought)-questions involved do not admit of true or false answers that can be scientifically determined. Thus, solutions can only be judged (subjectively) as ‘good’ or ‘bad’. The argumentative model and information systems aim at facilitating participants’ efforts to explain to each other their basis of these subjective judgments; at best, to ‘objectify’ the judgments, by showing each other how their ‘good/bad’ judgments relate to objective features of the solution. This is a model whose essential dependency on participation required openness to creativity (new ideas), common language, avoiding discipline jargon as much as possible (or translating jargon into common language), and openness to different frames of references about the matter under discussion.

Alexander’s Pattern Language can be seen as representing a very different view. It was an ambitious, eminently insightful and creative attempt to establish a different ‘way of talking’ — a language — about architecture, construction, and urban design, addressing aspects that contemporary architecture and urban planning as well as the efforts of the systems approach as well as the building systems developers (another area of research and study at Berkeley) had largely been missing, and as such immensely valuable.

But essentially, the Pattern Language is another element in a long line of what may be called ‘rule books’ or recipe books – a somewhat dismissive label that does not do justice to its significance was ‘cookbook’ — for building and urban design. A collection of solution elements that — like a good cookbook — promised, even guaranteed a ‘good’ solution if the solution was put together by properly following the recipe. Potential objections such as that of resulting uniformity were countered by pointing to the large number of different possible combinations of the patterns, and the claim that designers could ‘apply the same patterns a thousand times without doing it the same way twice’ — obviously by virtue of dimensional, that is, parametric variations of the pattern elements. But the patterns had to be applied to solve the problem it claimed to address: Alexander sternly warned that if you are not using the pattern, you aren’t solving the problem…
An added attraction for some minds: since the patterns are so timelessly valid and true, there’s no more need for discussion, argument. Disagreements about pros and cons of solutions can be shut down just like Alexander shut up a young developer at one of his presentations who dared ask a question about the economic implications of the approach: “We are talking about serious things here…”

I was of course working in the ‘other’ (Rittel) camp, trying to make useful contributions to some challenges of the argumentative model, such as developing tools for more systematic and transparent evaluation of planning arguments (the pro and con arguments about planning proposals, that did not receive much attention by the disciplines ‘in charge’ of argumentation because they contain deontic claims that are not ‘true’ of ‘false’ in the same way as the claims about the facts of the world, and because their structure does not meet the formal logic criteria for deductive validity.) And thinking about better ways to link the eventual decisions to the merit of the arguments and other information provided in the participatory planning and policy discourse, as well as better platforms for the planning discourse, especially for global problems — problems for which there are no useful recipe or cook books yet.

But I was fascinated by the Pattern Language effort, and tried to develop a different ‘way of talking’ about architecture in response to it, that in my opinion left more room for more room for creativity in addressing changes in people’s expectations of and responses to buildings, avoiding its exclusive ‘timeless’ aspect. [6] I also wanted to reopen the question of evaluation of solutions (in view of solutions and arguments that are not yet in the rule books) that the Pattern Language had subtly circumvented with the (implied) assurance that “if it’s done according to the rules and recipes, it is automatically good.”

Some of the Pattern Language adaptations I see in other areas seem to suffer from a common shortcoming of many ‘ways of talking’ — that of requiring would-be participants in the discourse to first learn yet another ‘language’, a new vocabulary. This is, in my opinion, a problem for the many ‘systems’ approaches and models, and arguably a reason for the lack of wider public acceptance of systems tools some systems thinkers complain about. It is a syndrome that can carry the danger of stifling participation, precisely by those people who have some of the desperately needed ‘distributed’ information. It also seems to — again, after Rittel’s and others’ valiant critique of the ‘expert model of planning’ — favor the role of experts — the ones who master the new vocabulary and therefore control the process and decisions — but who might be missing vital information; experts whose judgment about what makes a good solution may be disastrously different from those who will have to live with the consequences of the plans.

This leads me to the following urgent suggestion: that all proposed ‘Pattern Language’ adaptations in other realms be amended with the routine ‘Wrong question?’ reminder: Are the patterns in the rule collection appropriate and applicable to the respective situation — a situation that may be unique, new and unprecedented? Are there legitimate differences of opinion about the outcomes? And if there are even slight doubts in that respect, to include provisions for opening the discourse to information contributions that are not necessarily framed in the adopted pattern vocabulary, as well as abandoning the assumption that the quality or ‘goodness’ of solutions generated by the pattern language recipes is guaranteed by having followed the recipe.

Notes and references:

[1] Since the Pattern Language is not one of my prime areas of concern, I did not keep careful track of all these projects and thus may have missed many of these efforts. Helene Finidori’s report on a pattern language development on the issue of the Commons – ‘A Pattern Language (re)Generative of Commons’ by The Commons Abundance Network (http://commonsabundance.net/groups/a-pattern-language-regenerative-of-commons/) — triggered closer attention since the Commons issue was one of the major proposed answers to the Ban Ki Moon call for ‘revolutionary thinking and action to ensure an economic model for survival’ at the 2011 World Economic which led to a huge LinkedIn discussion on the STW network, and I studied some of the issues related to the Commons in more detail. Other examples of PL applications to fields outside of architecture and urban design that I ran across are the following (in no particular order, and just to indicate the variety of topics):

– Perkins, J et al :‘A Cleanroom Pattern Language: A Pattern Language Enters the Cleanroom – A Strategy for Humanizing the Cleanroom’. M+W Group Architecture USA Cleanroom Focus Group/ (http://dev.apptheneum.com.php54-2.ord1-1.websitetestlink.com/cleanroom-pattern-language/)
– Pollard, D.: ‘A Pattern Language for Effective Activism’ (http://www.generationalpha.org/);
– ‘Group Works: A Pattern Language for Bringing Life to Meetings and Other Gatherings’ (http://groupworksdeck.org)
– ‘A Pattern Language for Infosec’ (http://www.doinginfosecright.com/)
– Shuler, D.: ‘A Pattern Language for Living Communication’ / Liberating Voices Pattern Language System; (http://www.publicsphereproject.org/patterns/)
– Shen, L:‘A Pattern Language for Residential Energy Efficiency’ (http://homeenergypros.lbl.gov/
– Kelly, Allan: ‘Business Patterns for Software Developers’ (E-book: John Wiley & Sons, 2012)
– ‘A Proposal for Collaboration on a Pattern Language for Service Systems’ (Science, Management, Engineering and Design) by David Ing (http://coevolving.com/commons/publications);
– ‘A Database Integrity Pattern Language’ by O. P. Rotaru and M. Petrescu, Leonardo Journal of Sciense, Issue 5, July-December 2004 pp 46-62;
– S. Denef, R. Opper,amm, D. Keyson: ‘Designing For Social Configurations: Pattern Languages to Informs the Design of Ubiquitous Computing’, International Journal of Design Vol. 5 No. 3, 2011;
– Kyle Denlinger: ‘Pattern Language for eLearning’ (http://www.slideshare.net/denlinkd07?utm_campaign=profiletracking&utm_medium=sssite&utm_source=ssslideview;
– Robert Waller, Judy Delin et Martin Thomas ‘Towards a Pattern Language Approach to Document Description’ Discours: Revue de linguistique, psycholinguistique et informatique. 10, 2012; (http://discours.revues.org/)
– The 2013 ‘Pattern Languages of Programs Conference, Monticello, IL. hosted a number of papers on Pattern Language Applications, e.g.:
– Brown, K: “Cloud Computing Patterns”
– Goswami, D: “Hierarchical Rules Patterns for Validating System Configurations”
– Overbey, J.: “Immutable Source[Mapped Abstract Syntaxt Tree: A Design Pattern for Refracturing Engine APIs”
– Reza, J: “Mobile Apps Multi-Platforms Design Pattern Featuring Translator for Interactive Animation Components”
– Rubis, R and I. Cardei: “The Common Business Object Pattern”
– Correia, F and A. Aguiar: “Patterns of Flexible Modeling Tools”
– Reza, J: “Supervenience as a Design Pattern: Its Realization in Object-Oriented Languages”
– Villareal, I, Fernadez, E., Larrondo-Petrie, Hashzume, K: “A Pattern for Whitelisting Firewalls”
– Preschern, C, Kaitazovic, Kreiner, C.: “Security Analysis of Safety Patterns”
– Mana, A, Fernandez, E., Ruiz, J., Rudolph, C.: “Towards Computer-Oriented Security Patterns”
– Li, Y., Runde, R., Stole, K.: “Towards a Pattern Langauge for Securoity Risk Analysis of Web Applications”.

[2] Alexander, Christopher (1975). The Oregon Experiment. Center for Environmental Structure. Oxford University Press, USA. ISBN 978-0195018240.
Alexander, Christopher et al.: (1977). A Pattern Language. Center for Environmental Structure. Oxford University Press, USA. ISBN 978-0195018240.
Alexander, Christopher (1979). The Timeless Way of Building. Center for Environmental Structure. Oxford University Press, USA. ISBN 978-0195024029.

[3] While Rittel had been talking about the concept of ‘Wicked Problems’ for some time in his lectures at Berkeley, the first publication was the 1972 Policy Science article by Horst W.J. Rittel and M. Webber: “Dilemmas in a General Theory of Planning”.

Since many references and proposals advertised as tools for ‘solving wicked problems’ as well reviews referring to them as problems that ‘can’t be solved’ are often based on misunderstanding and misrepresentation of these problems, it may be useful to summarize their key features (summarized from the ‘Dilemmas’ paper:

– There is no definitive formulation of a WP. Every statement about their definition is a statement about one of many conceivable solution ideas (so the problem can’t be definitively stated until a ‘solution’ has been adopted);

– A WP can be considered to be a symptom of another problem.

– Every WP is essentially unique.

– There is no well-described set of permissible steps or operations to be brought to bear on WP’s (as in the basic operations of addition, subtraction, multiplication etc. in mathematics): anything goes;

– The discrepancy representing a WP can be explained in numerous ways. The choice of explanation determines the nature of the problem’s resolution.

– WP’s have no stopping rule (such that the procedure tells problem-solvers when they are ‘done’); any ‘solution’ can be refined and improved, or there might still be other alternatives that could be investigated and examined;

– The information needed to solve WP’s is not exclusively found in textbooks or experts’ professional knowledge, but is typically ‘distributed’ in the population of people being affected by the problem or by proposed solutions (so that the affected population changes with every different solution alternative considered…)

– WP’s do not have an enumerable (or exhaustively describable) set of potential solutions. There may be many ‘solutions’ to the problem, or none at all;

– Solutions to WP’s are not ‘correct or ‘false’ — they are judged ‘good’ or ‘bad’ — and people differ in their judgments about this (depending on whether they are getting the benefits of a solution or having to bear its costs…);

– There is no immediate and no ultimate test of a solution to a WP.

– Unlike ‘tame problems’ where you one try again if a first solution attempt has not worked out, WP solutions are typically ‘one-shot’ operations: any intervention effort consumes resources and creates new conditions that make it a different problem. There is no opportunity to learn by trial and error: every attempt counts significantly.

– Unlike ‘tame problems’ in science, where ‘failed’ attempts to confirm a hypothesis do have merit (contributing to our knowledge about what ‘works and what doesn’t, WP-solvers have no ‘right to be wrong’ and are liable for the consequences of solutions or for the failure to provide a solution.

With WP’s understood in this way, consultants’ claims that their approaches will help clients ‘solve’ Wicked Problems should be regarded with suspicion.

[4] The split, as I remember, was pronounced in an 1970 interview in the ‘Design Methods Newsletter” (later Design Methods and Theories Journal).

[5] Key publications of these proposals were:
– Kunz, W. and H. Rittel: (1970) “Issues as Elements of Information Systems”, Working Paper No. 131, Institute of Urban and Regional Development, University of California, Berkeley, 1970.
– Rittel, H. W.J: APIS: A Concept for an Argumentative Planning Information System. Working Paper No. 324. Berkeley: Institute of Urban and Regional Development, University of California, 1980.
A number of experimental applications of the underlying concepts were studies done at the ‘Studiengruppe für Systemforschung ‘(‘Systems Research Group’, Heidelberg), e.g. a proposal for an issue based information system for the West German Parliament, using demonstration material on proposed legislation on urban renewal for the West German Parliament; a study on improved utilization of higher education resources in the Federal Republic of Germany, and a proposal for an international Environmental Planning Information System (‘UMPLIS’).

[6] In a first 1980 paper in the Design Methods and Theories Journal, ‘Places and Occasions’, I suggested the aim of architecture to be to provide places inviting and facilitating the occasions our lives consist of, and that the design of the places should evoke imagery supporting the users’ own image concepts of who they are (or ought to be) and what kind of activity is involved in the occasion. Later papers addressed the development of techniques for measuring the image appropriateness of designs, testing the theory by using it for the interpretation of historical buildings, and suggesting its use to develop measures of value of built environments. Key differences between this perspective and the Pattern Language are that the core concepts or elements are not the physical design patterns but the activities they accommodate, and the images they evoke to support and inspire those experiences. The role of past information is acknowledged, but I suggest that this view better explains the changes in built environment design over time, not just focusing on ‘timeless’ patterns), accounting for the desire of each new generation to ‘make a difference’ by creating its own way of life while building on the past; different groups developing their own occasions and corresponding image expressions in the details of their building and cities.


6 Comments on “A personal note on Pattern Language applications in other fields”

  1. Samuel A. Horton says:

    I am currently working toward my MBA and have been exposed to various forms of systems thinking and economics that I was not formally exposed to in Architecture school. While systems thinking is useful for the expert as a way of viewing a problem its application to find widely accepted and valued architectural solutions is in my view limited. Economics makes a basic assumption that people are rational. However, we know from numerous studies that people act in many irrational ways. This does not mean that economics is not useful, it only means that it can not explain the market completely or at micro scales.
    I would suggest that there may be some value in how architecture may relate to marketing theory. Marketers have found ways to utilize aspects of pattern language to reach potential consumers and influence them in many ways. The roots of many of these techniques are rooted in psychology that span generations and cultures. It seems that there may be some common ground between methods of generating and evaluating marketing ideas. Architecture markets to the user on a daily basis.

  2. abbeboulah says:

    thanks for your comment; though I’m not sure I get your point. Of course sets of recommendations or rules are useful, even necessary, in most areas of life — whether you call them rules, regulations, laws, tips or patterns. So this would apply to marketing as well — though I don’t know enough about marketing to be a good judge about that.

    In general, however, it seems that you can describe any two things or circumstances in terms of what they have in common, — or you can focus on their differences. Both are equally legitimate and meaningful. Depending on whether the commonalities or the differences are considered more significant, however, the lessons or guidelines you draw from them will be different: from the former you can derive rules or patterns; from the latter, you get may be able to draw insights on what to do to deal with the different circumstances, get the information, evaluate possible approaches, arrive at decisions. And you will draw different levels of confidence about those decisions. The rules and patterns aim at making you certain that the solution is ‘correct’, or ‘good’, based on having followed the rules. The decisions we make in dealing with problems we acknowledge as ‘wicked’ offer much less in terms of certainty, suggesting more humility. The military is very good at developing and insisting on following rules, as far as I know, and it depends very much on keeping the troops confident about what they are doing. Yet — leaving the percentage of wars settled as ‘undecided’ aside — half of all armies lose their wars… I suspect, largely because the rules their generals drew from the centuries of experience with warfare and so rationally followed just didn’t apply to the new conflict.

    I’d be interested in some examples of the aspects of pattern language used by marketing.

    About economics and architecture, you might be interested in some of my more recent writings about the value of the built environment based on occasions and image (issues I did mention my classes), that standard economics as applied to building has not been able to address well. (I noted that already in my attempt to introduce some economic thinking into architectural education with my old 1992 textbook of Building economics for Architects).

  3. daviding says:

    Thank you for the historical context on the alternative approaches (and changes) in the Berkeley microcosm of Christopher Alexander and Horst Rittel. This writing confirms a history related to me by my friend David Hawk, about how the pattern language and argumentative approaches are in opposition with each other.

    I have recently been researching pattern language — towards a potential “Service Systems Thinking” direction”, to the point of attending PLoP and AsianPLoP conferences. At my core, however, I’m a systems thinking advocate, coming down through the West Churchman lineage.

    The IBIS/APIS approach brings a perspective that I appreciate. There would a great value if there was a new synthesis of the pattern language and argumentative approaches. This might not be easy … but is worth thinking about.

    • abbeboulah says:

      David, thank you for your comment. The ‘opposition’ you mention between the Pattern Language and the argumentative approaches, to my mind is less a substantial one than one arising out of Alexander’s dramatic split from the design methods/systems approach movement, based perhaps on his disappointment with his own earlier efforts in the systems camp, and his desire for providing something more immediately practical and applicable to the but environment design folks. The projects we were working on with Rittel were not architecture or building projects at all — I I was involved in an IBIS project (the first one as far as I know) trying to map some proposed urban planning legislation as the demo project for a proposed IBIS component for the German parliament, and a larger one dealing with approaches to improve the utilization of higher education resources. There were proposals for an Environmental Protection / Planning IBIS at the UN level. Only one (Dehlinger) worked on an actual Building IBIS, that I don’t now much about.

      But Rittel was much less concerned about that split; as part of his argument that the basic question-answer format of the IBIS would be able to accommodate any other conceptual input of other perspectives. I perceived the patterns as examples of the IBIS items Rittel called ‘model issues’ — which he understood as more or less standard or widely accepted general models that were applicable across a wide spectrum of domains, e.g. the centralization / decentralization, but also could include such things as standard accepted technical or procedural rules. As I indicated in the post, architecture is a domain in which both expectations (‘I want a two-bedroom house with garage…)’ and technology — available building materials, regulations norms, etc. already is full of patterns — rule-like elements.

      Where there were significant and fundamental differences was Alexander’s insistence of ‘value’ as an objective phenomenon, embedded in patterns — which guaranteed a valid result when applied properly, and therefore did not require evaluation or argumentation processes as part of the design and planning process. I don’t think that this problem has been adequately resolved yet.

      From a systems perspective, we can of course argue that anything can be perceived and described as a system, and the patterns with their ‘part-of’ and other relationships fit the bill perfectly. So I have been much more concerned about the mutual accommodation problems of the argumentative model and (most) systems tools around — see my last and some other recent posts: the fact that the complexity of systems models is not easily represented in the kinds of arguments we use in planning discourse, while the typical systems models don’t even acknowledge questions and arguments about their model assumptions.

      • daviding says:

        Thorbjoern, thanks for the response. Your first-hand accounts of the history of science at Berkeley are helpful.

        (1) In the blog post, footnote [6] mentions the “Places and Occasions” in Design Methods and Theory Journal 1980. Some university library searches suggest that electronic versions of the journal don’t go back that far. I have found an 1989 EDRA 20 paper on “The Need for Intermediate Level Paradigms” at http://www.edra.org/sites/default/files/publications/EDRA20-Mann-76-81.pdf . Does this cover substantially the same content? Alternatively, could you post a libre version of the 1980 article?

        (2) I’m interested in the idea of “model issues” that you’ve surfaced, as a perspective on patterns. Could you clarify that? (A search on rittel “model issues” seems to find instances where model is a verb, but I think that in your context it’s either a noun or an adjective). In the PLoP community, there’s a distinction between a pattern language and a pattern catalog, in that a pattern language should be generative, whereas a pattern language could be only descriptive. Are “model issues” a set of recurring issues that would be equivalent to a pattern catalog?

        (3) Alexander’s insistence on wholeness / living / quality without a name as an objective phenomenon is a challenge. In his later work, I think that the unfolding wholeness is not in the patterns, but in the combinations related to systems of centers. There is some systems thinking related to containing wholes (i.e. hierarchy) in laying out (i) the system of centers in the buildings with (ii) the system of centers in the land, described in The Battle for Life and Beauty on the Earth (2012). I haven’t fully written out my understanding (not necessarily agreement) of Alexander’s approach, but recently presented some slides on this at http://coevolving.com/commons/20150228-unfolding-values-in-places-spaces-and-paces.

        In addition, when we move out of the domain of built environments into service systems, the roles or positions of multiple parties becomes more overt. Requiring an appreciation of the variety of stakeholders such as beneficiaries, sponsors, funders, etc. would suggest either subjectivities or multiple objectivities.

        (3) I’ve also been looking at the way systems diagrams have been constructed. After some time spent with SysML at INCOSE, I’m seeing more promise in Object Process Methodology, encouraged by Dov Dori at http://esml.iem.technion.ac.il/ . While there are sophisticated tools associated with OPM, the idea of representing objects (structures) as boxes and processes as ovals is simple yet extensible. I’ve suggested some preliminary directions on Service Systems Thinking at http://coevolving.com/blogs/index.php/archive/incubating-service-systems-thinking/ … with much work to be done in years to come. This has favoured the pattern language approach so far, and our exchange has me thinking about how IBIS/APIS orientations might complement

  4. abbeboulah says:

    David, thanks for the comments and your interest. Let me try to answer your questions one by one.
    1) The first article on my ‘occasions / image view of architecture in the Design Methods Journal was written in the per-personal computer age. I could try to dig out the article from the archives, scan it and send it to you. If it’s the content you are interested in, i have some more recent draft chapters in a book I’m trying to get done, and a more recent article (‘The Value of Built Environment as a Function of Occasion and Image’ — also on Academia.edu) that I could sent you as email attachments to your personal email address.
    2) I remember Rittel’s ‘model issues from personal discussions and the first IBIS projects we did long ago, but can’t point to a publication. As I mentioned, one example of his take on model issues was the centralization question — an issue for public services of any kind, but also pertinent for larger companies, as to whether and how much the management and distribution provisions should be done by a central entity, or decentralized into many smaller, local branches. The arguments for and against are fairly standardized across many application domains — that is, you can have a set of pro and con arguments in a ‘model bank’ section of the IBIS, that can be drawn upon for any new case where centralization/decentralization decisions must be made. I personally consider many issues for which there are well-known standard solutions, such as the road intersection question, to be model issues. The cloverleaf pattern for freeway interchanges Alexander mentions in his PatternLanguage book, is such a kind of ‘model issue’ answer — adapted to local conditions such as expected traffic volume and landscape context as necessary; other ‘model answer’ is the roundabout, and the straight intersection with traffic lights. Not sure if that matches Rittel’s view.
    3) The ‘wholeness’ discussion is one I try to stay away from, since it often seems to be little more than a vague rhetorical tool attacking some perspective and promoting another. You can’t argue with it, but it does not help creating better solutions and making decisions. Staying with the patterns as example: any pattern is part of a larger pattern, — the larger ‘whole’ — but contains a number of smaller patterns for which IT is the whole. The debate can take silly forms known as the ‘doorknobbing’ syndrome.
    In your sentence “, there’s a distinction between a pattern language and a pattern catalog, in that a pattern language should be generative, whereas a pattern language could be only descriptive.” you probably intend the second ‘language’ to be ‘catalog’, and I agree that a catalog of model answers is more descriptive that generative, but the whole package is entirely ‘normative’, wouldn’t you say? With instructions for how one can ‘generate’ solutions by picking items from the catalog and connecting them according to the rules given in each pattern?
    4) Systems diagrams are too varied for me to keep track of. The simple understanding of ‘system’ as a structure of elements or components connected by relationships permits untold varieties of applications as well as choices of symbols for the elements and relationships. Seen from this perspective, the Pattern Language is of course a system — the elements are the patterns, the relationships are the part-whole connections.
    These are some first comments — I haven’t had time to look at your links yet.

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