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86
NATO SOFTWARE ENGINEERING CONFERENCE 1968
8. Invited Addresses
to find out how to load it. The problems with Sysgen are not to be dispensed with, they are inherent. But why do we need to take atoms down from the shelf? What you want is a description which you can understand, because the time taken to code it into your own system is really very small. In that way you can insert your own nuances. The first step in your direction should be better descriptions.
Endres: Two notes of caution: You discarded the algorithms in the Comm. ACM in part because they are written in high-level language, so I understand that you refer to routines written in a more machine oriented language. I think you oversimplify the problem of transliteration. Or do you assume a de facto machine standard? Second question: You refer to the problems of Sysgen, where you cut out pieces from a large collection. If instead you want to put together systems, I think the problems of Sysgen become a dimension larger. Who will bear this cost, and maintain the system?
McIlroy: The algorithms in the Communications of the ACM effectively use one language, which is suitable for a particular class of applications. This may not be the right one for things like input/output packages. On the second question: I am convinced, with you, that at first it will be harder to build systems by accretion, rather than by excision. The people who build components will have to be skilled systems builders, not run of the mill users.
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Kjeldaas: I strongly favor this idea. I think the examples mentioned are within the state of the art. However, later we will want macros needing parameters having more intricate relations, for instance if you want some functional relationship between the parameters. We will need some language for describing the parameters. Another point: documentation can also be included in this. When you have given the parameters to the program, you can give the same parameters to the documentation, and the documentation for the particular use can be produced automatically. Catering for different machines will raise big problems, needing research.
Kolence: May I stress one point: McIlroy stated that the industrialization is concerned with the design, not the replication process. We are concerned with a mass design problem. In talking about the implementation of software components, the whole concept of how one designs software is ignored. Yet this is a key thing.
Naur: What I like about this is the stress on basic building principles, and on the fact that big systems are made from smaller components. This has a strong bearing on education. What we want in education, particularly at the more elementary level, is to start indoctrinating the knowledge of the components of our systems. A comparison with our hardware colleagues is relevant. Why are they so much more successful than we are? I believe that one strong reason is that there is a well established field of electronic engineering, that the young people start learning about Ohm’s Law at the age of fourteen or thereabouts, and that resistors and the like are known components with characteristics which have been expounded at length at the early level of education. The component principles of our systems must be sorted out in such a form that they can be put into elementary education.
Gill: Two points: first on the catalogue question. I hope we can do better than the Sears-Roebuck catalogue. Surely what we want is a computerized conversational catalogue. Second point: what is it that you actually sell when you sell a piece of software, what exactly does a software contract look like?
Barton: McIlroy’s talk was so well done that it took me about three minutes to realize what is wrong this idea. Another compliment: If I were running Intergalactic Software, I would hire McIlroy for a manager. Now the serious point: Over the last few years I have taught the ACM Course  Information Structures and used the game not to let anyone code or write anything in any programming language at all. We have just thought about data representations. If in this way you get people over the habit of writing code right away, of thinking procedurally, then some very different views on information representations come to view. In McIlroy’s talk about standard components having to do with data structures I have the feeling that this is not a problem to take out of the universities yet. Now a heretical view: I don’t think we have softened up enough things in machines yet. I don’t think we will get anywhere trying to quantify the space-time trade-off unless we discard fixed word sizes, fixed character sizes, fixed numerical representations, altogether in machines. Without these, the thing proposed by McIlroy will prove to be just not quite practical.
Fraser: I wish to take issue with d’Agapeyeff. I think it will be possible to parameterize data representation and file management. From a particular file system experience I learned two lessons: first, there are a large number