# Institution (computer science)

The notion of **institution** was created by Joseph Goguen and Rod Burstall in the late 1970s, in order to deal with the "population explosion among the logical systems used in computer science". The notion tries to capture the essence of the concept of "logical system".[1]

The use of institutions makes it possible to develop concepts of specification languages (like structuring of specifications, parameterization, implementation, refinement, development), proof calculi and even tools in a way completely independent of the underlying logical system. There are also morphisms that allow to relate and translate logical systems. Important applications of this are re-use of logical structure (also called borrowing), heterogeneous specification and combination of logics.

The spread of institutional model theory has generalized various notions and results of model theory, and institutions themselves have impacted the progress of universal logic.[2] [3]

## Definition

The theory of institutions does not assume anything about the nature of the logical system. That is, models and sentences may be arbitrary objects; the only assumption is that there is a **satisfaction relation** between models and sentences, telling whether a sentence holds in a model or not. Satisfaction is inspired by Tarski's truth definition, but can in fact be any binary relation.
A crucial feature of institutions is that models, sentences, and their satisfaction, are always considered to live in some vocabulary or context (called **signature**) that defines the (non-logical) symbols that may be used in sentences and that need to be interpreted in models. Moreover, **signature morphisms** allow to extend signatures, change notation, and so on. Nothing is assumed about signatures and signature morphisms except that signature morphisms can be composed; this amounts to having a
category of signatures and morphisms. Finally, it is assumed that signature morphisms lead to translations of sentences and models in a way that satisfaction is preserved. While sentences are translated along with signature morphisms (think of symbols being replaced along the morphism), models are translated (or better: reduced) **against** signature morphisms: for example, in case of a signature extension, a model of the (larger) target signature may be reduced to a model of the (smaller) source signature by just forgetting some components of the model.

Formally, an institution consists of

- a category
of
**signatures**, - a functor
Set giving, for each signature
, the set of
**sentences**, and for each signature morphism , the**sentence translation map**, where often is written as , - a functor
Cat giving, for each signature
, the category of
**models**, and for each signature morphism , the**reduct functor**, where often is written as , - a satisfaction relation for each ,

such that for each
in
the following **satisfaction condition** holds:

if and only if

for each and .

The satisfaction condition expresses that truth is invariant under change of notation (and also under enlargement or quotienting of context).

Strictly speaking, the model functor ends in the "category" of all large categories.

## Examples of institutions

## Notes

- J. A. Goguen and R. M. Burstall, Institutions: Abstract Model Theory for Specification and Programming, Journal of the Association for Computing Machinery 39, pp. 95–146, 1992.
- Razvan Diaconescu, "Three decades of institution theory" in Universal Logic: An Anthology edited by Jean-Yves Béziau 2012 Springer ISBN 978-3-0346-0144-3 pp 309-322
- T. Mossakowski, J. A. Goguen, R. Diaconescu, A. Tarlecki, "What is a Logic?", '. In Jean-Yves Beziau (Ed.), Logica Universalis: Towards a General Theory of Logic, pp. 113–133. Birkhäuser, Basel, 2005, 2nd Edition 2007.

## References

- J. A. Goguen and R. M. Burstall, Introducing Institutions, Lecture Notes in Computer Science 164, pp. 221–256, 1984.
- J. Meseguer, General Logics, Logic Colloquium 87, pp. 275–329, North Holland, 1989.
- J. A. Goguen and G. Rosu, Institution morphisms, Formal aspects of computing 13, pp. 274–307, 2002.
- D. Sannella and A. Tarlecki, Specifications in an arbitrary institution, Information and Computation 76, pp. 165–210, 1988
- R. Diaconescu, Institution-independent Model Theory Birkhäuser, Basel, 2008,

## External links

- "Institution Theory".
*Internet Encyclopedia of Philosophy*. - Institutions by Joseph Goguen
- Formalism, Logic, Institution - Relating, Translating and Structuring (including large bibliography)
- Razvan Diaconescu's publication list - contains recent work on institutional model theory