La logique informatique
(selon les travaux de J.D WARNIER)
L.C.P Logic of Programs construction
What has happened since the beginning of programming !
Maybe you will find me a bit old-fashioned, but remember the story, seems to me quite essential if you want to understand the present.
Once upon a time ! It happens in the 60s (the sixties .., a great time !) Computers arrive and with them, the trouble to program them, what an adventure! We had at our disposal the few instructions necessary to "read" data, perform calculations, make conditional connections and finally "write" the data at the output of the program.
It was therefore necessary to ensure that all these instructions were executed in an orderly manner and under certain conditions. It was therefore necessary to be able to represent in time and space the scheduling of these instructions in the form of an organization chart such as this one:
A rectangle was designed to represent a set of instructions to be executed at a specific point in the program.
An arrow connecting two rectangles or diamonds represents a systematic connection.
A diamond represents a test to condition or not a connection to a rectangle or other diamond !.
You will agree with me that this type of representation of a program has a number of drawbacks:
1 °) We do not see very well what a rectangle represents, it can express :
- Let a sequence of instructions be executed under the same conditions,
- A large function of the program requiring a large number of instructions, not necessarily executed under the same conditions,
- Either an instruction to which the programmer wants to give special importance.
- Etc ..
2 °) Treatments and connections make it very difficult to understand the chronological of sequences. This being most often due to the fact that a diamond may express either a simple condition or a complex condition.
3°) In a representation such as that proposed, it is very difficult, if not impossible, to derive a hierarchical view among all sets of instructions, the direct consequence of which is to work at the level of detail, and not at the whole level, consequently a total ignorance of data repository (Or structure) in which a rectangle is situated, and thus of the problem in general.
It was necessary to do something, for besides the fact that this kind of solution could only be concocted by small geniuses, it also became almost impossible to make any modifications except by the computer scientist ( Irreplaceable) who had written it ! (and even) !.