Agile Software Development
Автор: Alistair Cockburn /
APPENDIX B: Naur, Ehn, Musashi Peter Naur, Programming as Theory Building
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Часть 2
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In the years following these events the compiler developed by group B was taken over by other programmers of the same organization, without guidance from group A. Information obtained by a member of group A about the compiler resulting from the further modification of it after about 10 years made it clear that at that later stage the original powerful structure was still visible, but made entirely ineffective by amorphous additions of many different kinds. Thus, again, the program text and its documentation has proved insufficient as a carrier of some of the most important design ideas.
Case 2 concerns the installation and fault diagnosis of a large real-time system for monitoring industrial production activities. The system is marketed by its producer, each delivery of the system being adapted individually to its specific environment of sensors and display devices. The size of the program delivered in each installation is of the order of 200, 000 lines. The relevant experience from the way this kind of system is handled concerns the role and manner of work of the group of installation and fault finding programmers. The facts are, first that these programmers have been closely concerned with the system as a full time occupation over a period of several years, from the time the system was under design. Second, when diagnosing a fault these programmers rely almost exclusively on their ready knowledge of the system and the annotated program text, and are unable to conceive of any kind of additional documentation that would be useful to them. Third, other programmers' groups who are responsible for the operation of particular installations of the system, and thus receive documentation of the system and full guidance on its use from the producer's staff, regularly encounter difficulties that upon consultation with the producer's installation and fault finding programmer are traced to inadequate understanding of the existing documentation, but which can be cleared up easily by the installation and fault finding programmers.
The conclusion seems inescapable that at least with certain kinds of large programs, the continued adaption, modification, and correction of errors in them, is essentially dependent on a certain kind of knowledge possessed by a group of programmers who are closely and continuously connected with them.
Ryle's Notion of Theory
If it is granted that programming must involve, as the essential part, a building up of the programmers' knowledge, the next issue is to characterize that knowledge more closely. What will be considered here is the suggestion that the programmers' knowledge properly should be regarded as a theory, in the sense of Ryle [1949]. Very briefly, a person who has or possesses a theory in this sense knows how to do certain things and in addition can support the actual doing with explanations, justifications, and answers to queries, about the activity of concern. It may be noted that Ryle's notion of theory appears as an example of what K. Popper [Popper, and Eccles, 1977] calls unembodied World 3 objects and thus has a defensible philosophical standing. In the present section we shall describe Ryle's notion of theory in more detail.
Ryle [1949] develops his notion of theory as part of his analysis of the nature of intellectual activity, particularly the manner in which intellectual activity differs from, and goes beyond, activity that is merely intelligent. In intelligent behaviour the person displays, not any particular knowledge of facts, but the ability to do certain things, such as to make and appreciate jokes, to talk grammatically, or to fish. More particularly, the intelligent performance is characterized in part by the person's doing them well, according to certain criteria, but further displays the person's ability to apply the criteria so as to detect and correct lapses, to learn from the examples o others, and so forth. It may be noted that this notion of intelligence does not rely on any notion that the intelligent behaviour depends on the person's following or adhering to rules, prescriptions, or methods. On the contrary, the very act of adhering to rules can be done more or less intelligently; if the exercise of intelligence depended on following rules there would have to be rules about how to follow rules, and about how to follow the rules about following rules, etc. in an infinite regress, which is absurd.
What characterizes intellectual activity, over and beyond activity that is merely intelligent, is the person's building and having a theory, where theory is understood as the knowledge a person must have in order not only to do certain things intelligently but also to explain them, to answer queries about them, to argue about them, and so forth. A person who has a theory in prepared to enter into such activities; while building the theory the person is trying to get it.
The notion of theory in the sense used here applies not only to the elaborate constructions of specialized fields of enquiry, but equally to activities that any person who has received education will participate in on certain occasions. Even quite unambitious activities of everyday life may give rise to people's theorizing, for example in planning how to place furniture or how to get to some place by means of certain means of transportation.
The notion of theory employed here is explicitly not confined to what may be called the most general or abstract part of the insight. For example, to have Newton's theory of mechanics as understood here it is not enough to understand the central laws, such as that force equals mass times acceleration. In addition, as described in more detail by Kuhn [1970, p. 187ff], the person having the theory must have an understanding of the manner in which the central laws apply to certain aspects of reality, so as to be able to recognize and apply the theory to other similar aspects. A person having Newton's theory of mechanics must thus understand how it applies to the motions of pendulums and the planets, and must be able to recognize similar phenomena in the world, so as to be able to employ the mathematically expressed rules of the theory properly.
The dependence of a theory on a grasp of certain kinds of similarity between situations and events of the real world gives the reason why the knowledge held by someone who has the theory could not, in principle, be expressed in terms of rules. In fact, the similarities in question are not, and cannot be, expressed in terms of criteria, no more than the similarities of many other kinds of objects, such as human faces, tunes, or tastes of wine, can be thus expressed.
The Theory to be Built by the Programmer
In terms of Ryle's notion of theory, what has to be built by the programmer is a theory of how certain affairs of the world will be handled by, or supported by, a computer program. On the Theory Building view of programming the theory built by the programmers has primacy over such other products as program texts, user documentation, and additional documentation such as specifications.
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