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L.C.S              organizing data in a computer system

Relating the sets (F.L.P) of a base

I would not teach computer scientists anything, but when we talk about a database, we are talking about sets of data that are defined precisely in terms of the mathematic law we have outlined earlier.

I would like to remind you :

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The elements of a set or if you prefer all the records of a file (FLP) must have the same format, in other words all the records (images of the objects) must be strictly identical (Bijection between the fields of all the records ). What prevents us from putting a priori anything in a file, as a result we will find ourselves in the presence of a large number of files, but how important ! We are no longer in the time when the first problems of the computer scientist was to save time and space in his computer system !, the important thing is to be clear and rigorous in logic.


We now have to worry about establishing the necessary relationships between all these files.
Here is THE MATHEMATICAL LAW that one must imperatively respect in computer science, to put two sets in relation:

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When two sets are connected,
It must be an application
In the mathematical sense of the term!

Explanation: When two sets are connected, each element of the set considered as the starting set corresponds to one and only one element in the arrival set.

Here is our base completed with the relationships between F.L.P's:

We must not forget, while we are there, to note the nature of the application :

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Injective, (0-1)
Surjective, (1-n)
Bijective, (1-1)
Any, (0-n)

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This will help you much later.

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A small example, the relation "command <-> command lines"  is surjective (A command to at least one command line or even more)

At this point, it seems good to make the following (often forgotten) remark. The primary data (FLP and Relations) are images and reflect reality at a moment T, so we must pay attention if It is necessary to date these images. We will have an opportunity to talk about this when we come to the study of secondary data.

Now that we have discovered our data containers,

                                                        let's put some stuff in!

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