Specification

Specification Writing (J. Christopher Jones)
Criteria (J. Christopher Jones)
Standards (James G. March & Herbert A. Simon)
Standards (C. West Churchman)
Objectives (J. Christopher Jones)
Objectives tree (Nigel Cross and Robin Roy)
Performance (L. Bruce Archer)
Performance (Nigel Cross and Robin Roy)
Boundaries (J. Christopher Jones)
Checklists (J. Christopher Jones)
Checklists (Nigel Cross and Robin Roy)

Specification Writing

[1982, First published 1970] J. Christopher Jones, Design Methods. Seeds of human future, John Wiley & Sons, New York
"Aim
To describe an acceptable outcome for designing that has yet to be done.”
"Outline
1. Provisionally identify a range of possible outcomes, of varying levels of generality.
2. Select the lowest level of generality that leaves the designers with sufficient design freedom.
3. Define the expected design outcome without reference to the design features that the designers are free to change and with reference to measures of performance that the designers will be able to predict."
(Method 6.4, p. 383)

Criteria

[1982, First published 1970] J. Christopher Jones, Design Methods. Seeds of human future, John Wiley & Sons, New York
"Aim : To decide how an acceptable design is to be recognized.”
"Outline
1. State an objective which has to be satisfied by any acceptable design.
2. Identify the ‘fail-safe’ direction, relative to the objective.
3. Examine the available evidence of the effects of departures from the objective and identify a condition that corresponds to the fail-safe side of the zone between acceptable and unacceptable designs.
4. Specify, as a criterion, the simplest measurement that will reliably indicate whether a design is on the fail-safe side, of this boundary.
5. Repeat steps 1 to 4 for each objective."
Note : "Selecting criteria is one of the most difficult parts of a designer’s task - the translating of aims and ideals into measurable realities. It calls for both scientific precision and artistic flexibility."
(Method 6.2, pp. 371-375)

Standards

[1966, First published 1958] James G. March & Herbert A. Simon, Organizations, Wiley & Sons, New York
“In making choices that meet satisfactory standards, the standards themselves are part of the definition of the situation.”
“The standard-setting process may itself meet standards of rationality: for example, an ‘optimizing’ rule would be to set the standard at the level where the marginal improvement in alternatives obtainable by raising it would be just balanced by the marginal cost of searching for alternatives meeting the higher standard.”
(Chapter 6, p. 141)

[1979, First published 1968] C. West Churchman, The Systems Approach. Dell Publishing, New York
“We need to create guidelines that will enable them [the performers] to do their job well. In other words, for each subsystem we are going to need a measure of the performance of the subsystem and a desired level of performance which we can call a ‘standard’ for the subsystem.” (Chapter 1, p. 7)

Objectives

[1982, First publihed 1970] J. Christopher Jones, Design Methods. Seeds of human future, John Wiley & Sons, New York
"Aim : To identify external conditions with which the design must be compatible.”
"Outline
- 1. Identify the situation within which the design is to operate.
- 2. Identify features of this situation with which the design must be compatible if it is to be accepted by the sponsors. These include:
(a) the sponsor’s expectations and the reasons for them
(b) the resources available
(c) the essential objectives.
Compatibility with these features is the ultimate objective.
- 3. Ensure that statements identifying the objectives are compatible with each other and with information that becomes available while designing." (Method 3.1, p. 194)

Objectives Tree

[1975] Nigel Cross and Robin Roy, Design Methods Manual. The Open University, Milton Keynes
Objectives Tree. “A method of listing the design objectives and sub-objectives in a project, and constructing a diagram of the hierarchical relationships between them.” (p. 49)
Procedure:
(1) List the known objectives for the project (these may initially be vague and at many levels of generality).
(2) Expand the list of objectives into sets of both higher-level and lower level objectives. (Ask: ‘what do we mean by x?’; ‘why do we want x?’ ‘How can we achieve x?’).
(3) Construct a diagrammatic tree of the objectives, showing the interconnecting ‘branches’ between objectives and their hierarchical relationships. (p. 49)
Note: “A clear statement of objectives clarifies for the designer the actions he should be taking and can provide a useful medium of communication when other people are also involved in the designing.” (p. 50)

Performance

[1969] L. Bruce Archer, The structure of the design process, in Geoffrey Broadbent & Anthony Ward editors, Design Methods in Architecture. Architectural Association Paper nº 14, Lund Humphries, London
“The set of criteria against which performance is measured is described here as ‘the performance specification’.” (p. 88)
“The superimposition of the domain of acceptability and the realm of feasibility were described as defining the arena in which an adequate performance must be developed.” (p. 89)

[1975] Nigel Cross and Robin Roy, Design Methods Manual. The Open University, Milton Keynes
Performance Specification. “Writing an accurate description of the performance required in a design solution, so as to allow an appropriate degree of freedom to the designer, and to allow an objective evaluation of any proposed solution.”
Procedure
(1) Identify different levels of generality applicable to the appropriate solution.
(2) Determine the level of generality at which you choose or are constrained to operate (in general choose the highest level that you have the freedom to go for).
(3) Identify the required performance attributes (having compiled a reliable list of attributes, you can write a performance specification for each attribute).
(4) Write succinct and precise statements of performance requirements for each attribute (state what the solution must do, not what it must be ; state limits)." (Performance Specification, p. 123)

Boundaries

[1970] J. Christopher Jones, Design Methods. Seeds of human future, John Wiley & Sons, New York, revised edition 1982
"Aim. To find limits within which acceptable solutions lie.”
"Outline
1. Write a complete set of performance specifications for the critical conditions
    that influence the dimension in question.
2. Define, as accurately as possible, the range of dimensions over which uncertainty exists.
3. Make a simulator in which the critical dimensions for each specification can be
    adjusted over the range of dimensions about which uncertainty exists.
4. Carry out performance tests to discover the limiting dimensions within which
    the specified performance can be achieved."
Note: "The principles of (a) incremental search; (b) simulation; (c) seeking limits instead of optima or single acceptable values, are applicable to many design situations."
(Method 1.5, pp. 134-148)

Checklists

[1982, First published 1970] J. Christopher Jones, Design Methods. Seeds of human future, John Wiley & Sons, New York
"Aim : To enable designers to use knowledge of requirements that have been found to be relevant in similar situations.”
"Outline
1. Prepare a list of questions that were found to be important in a similar
situation, or in several similar situations.
2. Ask some or all of these questions about the design that is to be evaluated."
Note: "Checklists are the simplest and perhaps the most immediately useful aids to design thinking that have appeared so far." (Method 6.1, pp. 362-369)

[1975] Nigel Cross and Robin Roy, Design Methods Manual. The Open University, Milton Keynes
Checklist: “A simple method of evaluating solutions against a set of previously established criteria or requirements.”
"Procedure
(1) Prepare a list of requirements that were found to be important in similar situations (of no use in completely novel situation).
(2) Check whether these requirements are satisfied in the design solution which is being evaluated."
Note: Checklists "can ... be used for other purposes ... such as listing objectives or questions to be answered."
(Checklist, pp. 129-130)

[Home] [Top]

Texts

Resources

Sites