Language, Logic and Modeling

Language is the parrot of thought, and a hard to teach one, nothing more. („Sprache ist der Papagei des Gedankens, und ein schwer gelehriger, nichts weiter.“) ― Friedrich Hebbel

Here's a short note about a perspective on logic for informatics, and decidedly not mathematics.

Formal logic has its roots in formalizing mathematics. Expressing the steps of reasoning in a formal system would assure us that there are no "gaps". I wrote a brief account on the beginnings of formal logic elsewhere.

The 20th century brought with it the advent of machines for information processing. This has gone way beyond mathematics already. In informatics (a better word for "computer science") one deals with information processing, and its practical kin, software engineering, deals with systems of all kinds where information gets in contact with reality.

There is a view that holds that we can only understand reality through models (see constructivist epistemology). Now, whether one subscribes to this or not, it is obvious that informatics relies on models of reality; information itself is always part of some model of reality. If you worked with customers or product managers, you know it is shaky and always incomplete series of models of reality, always adapting to new circumstances.

All I am saying is: formal logic can and should help us as a tool for formulate precisely these models. Like in mathematics, we do not want to have "gaps" in our reasoning. This is a somewhat ambitious direction, as software systems are not always built according to specification, and specifications are usually prose. And it is not only about modeling the domain.

"Functional programming" has gathered a large following in recent years, and I think this is because less because "software should be mathematics", but programmers benefit from constructing their code according to models that leaves no "gaps". The tool at hand, a (statically typed) functional programming languages, forces one to think thoroughly about data and the operations that are going to be carried out.

One does not need to resort to philosophy for challenging this. Large software systems are distributed over many machines, and gives rise to challenges that require methods different from those that are mathematics (and different from programs that run on a single machine). While functional requirements lead us to modeling domain concepts, designing a system that meets those is constrainted by non-functional requirements. We need to consider of performance and machine capacity, and evaluate which underlying technologies to build on, what guarantees they provide. It is here that engineering can be meaningfully distinguished from programming, and work is influenced less by theorems, more by best practices and experience.

Engineering and domain modeling are full of abstract models (the favorite tool being: diagrams of boxes with their meaning provided by handwaving). Formal logic and actual, manifest models where people could experiment are not encountered very often, yet expressing these models, reasoning with them and testing/verifying them would be critical since mistakes are costly. Moreover, a large number of people have to understand and act in accordance to these models. Often, the only time where this becomes obvious are the APIs between subsystems, a point where much modeling has already happened and cannot be changed.

I will go further and claim that Conway's Law is a consequence of each team forming their own "unit of modeling". It would be a lot better when we learnt to communicate explicitly and precisely what our models are, explain our needs to model things differently and how we can translate between our different models instead of insisting on some "right" way of seeing something. I place my hopes in logic as a language and tool to do just that. Mathematics is a discipline where the practice of modeling a mathematical "universe" has advanced very far, and it is no wonder that people seeking to use precise methods turn to it. It is a mistake to interpret this field of application of formal logic as some sort of mathematical monopoly. Language is a tool to communicate, a logic is a style of language.

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