45 research outputs found
Enriched categories as a free cocompletion
This paper has two objectives. The first is to develop the theory of
bicategories enriched in a monoidal bicategory -- categorifying the classical
theory of categories enriched in a monoidal category -- up to a description of
the free cocompletion of an enriched bicategory under a class of weighted
bicolimits. The second objective is to describe a universal property of the
process assigning to a monoidal category V the equipment of V-enriched
categories, functors, transformations, and modules; we do so by considering,
more generally, the assignation sending an equipment C to the equipment of
C-enriched categories, functors, transformations, and modules, and exhibiting
this as the free cocompletion of a certain kind of enriched bicategory under a
certain class of weighted bicolimits.Comment: 80 pages; final journal versio
Dynamic Tracing: a graphical language for rewriting protocols
The category Set* of sets and partial functions is well-known to be traced
monoidal, meaning that a partial function S+U -/-> T+U can be coherently
transformed into a partial function S -/-> T. This transformation is generally
described in terms of an implicit procedure that must be run. We make this
procedure explicit by enriching the traced category in Cat#, the symmetric
monoidal category of categories and cofunctors: each hom-category has such
procedures as objects, and advancement through the procedures as arrows. We
also generalize to traced Kleisli categories beyond Set*, providing a
conjectural trace operator for the Kleisli category of any polynomial monad of
the form t+1. The main motivation for this work is to give a formal and
graphical syntax for performing sophisticated computations powered by graph
rewriting, which is itself a graphical language for data transformation
Monoidal computer III: A coalgebraic view of computability and complexity
Monoidal computer is a categorical model of intensional computation, where
many different programs correspond to the same input-output behavior. The
upshot of yet another model of computation is that a categorical formalism
should provide a much needed high level language for theory of computation,
flexible enough to allow abstracting away the low level implementation details
when they are irrelevant, or taking them into account when they are genuinely
needed. A salient feature of the approach through monoidal categories is the
formal graphical language of string diagrams, which supports visual reasoning
about programs and computations.
In the present paper, we provide a coalgebraic characterization of monoidal
computer. It turns out that the availability of interpreters and specializers,
that make a monoidal category into a monoidal computer, is equivalent with the
existence of a *universal state space*, that carries a weakly final state
machine for any pair of input and output types. Being able to program state
machines in monoidal computers allows us to represent Turing machines, to
capture their execution, count their steps, as well as, e.g., the memory cells
that they use. The coalgebraic view of monoidal computer thus provides a
convenient diagrammatic language for studying computability and complexity.Comment: 34 pages, 24 figures; in this version: added the Appendi
Coalgebra for the working software engineer
Often referred to as ‘the mathematics of dynamical, state-based systems’, Coalgebra claims to provide a compositional and uniform framework to spec ify, analyse and reason about state and behaviour in computing. This paper addresses this claim by discussing why Coalgebra matters for the design of models and logics for computational phenomena. To a great extent, in this domain one is interested in properties that are preserved along the system’s evolution, the so-called ‘business rules’ or system’s invariants, as well as in liveness requirements, stating that e.g. some desirable outcome will be eventually produced. Both classes are examples of modal assertions, i.e. properties that are to be interpreted across a transition system capturing the system’s dynamics. The relevance of modal reasoning in computing is witnessed by the fact that most university syllabi in the area include some incursion into modal logic, in particular in its temporal variants. The novelty is that, as it happens with the notions of transition, behaviour, or observational equivalence, modalities in Coalgebra acquire a shape . That is, they become parametric on whatever type of behaviour, and corresponding coinduction scheme, seems appropriate for addressing the problem at hand. In this context, the paper revisits Coalgebra from a computational perspective, focussing on three topics central to software design: how systems are modelled, how models are composed, and finally, how properties of their behaviours can be expressed and verified.Fuzziness, as a way to express imprecision, or uncertainty, in computation is an important feature in a number of current application scenarios: from hybrid systems interfacing with sensor networks with error boundaries, to knowledge bases collecting data from often non-coincident human experts. Their abstraction in e.g. fuzzy transition systems led to a number of mathematical structures to model this sort of systems and reason about them. This paper adds two more elements to this family: two modal logics, framed as institutions, to reason about fuzzy transition systems and the corresponding processes. This paves the way to the development, in the second part of the paper, of an associated theory of structured specification for fuzzy computational systems
Protocol Choice and Iteration for the Free Cornering
We extend the free cornering of a symmetric monoidal category, a double
categorical model of concurrent interaction, to support branching communication
protocols and iterated communication protocols. We validate our constructions
by showing that they inherit significant categorical structure from the free
cornering, including that they form monoidal double categories. We also
establish some elementary properties of the novel structure they contain.
Further, we give a model of the free cornering in terms of strong functors and
strong natural transformations, inspired by the literature on computational
effects.Comment: Preprint. Article published in JLAMP. A few corrections have been
made to the previous versio
State-based components made generic
Genericity is a topic which is not sufficiently developed in state-based systems modelling, mainly due to a myriad of approaches and behaviour models which lack unification. This paper adopts coalgebra theory to propose a generic notion of a state-based software component, and an associated calculus, by quantifying over behavioural models specified as strong monads. This leads to the pointfree, calculational reasoning style which is typical of the so-called Bird-Meertens school.(undefined
Weighted automata as coalgebras in categories of matrices
The evolution from non-deterministic to weighted automata represents a shift from qual- itative to quantitative methods in computer science. The trend calls for a language able to reconcile quantitative reasoning with formal logic and set theory, which have for so many years supported qualitative reasoning. Such a lingua franca should be typed, poly- morphic, diagrammatic, calculational and easy to blend with conventional notation.
This paper puts forward typed linear algebra as a candidate notation for such a unifying role. This notation, which emerges from regarding matrices as morphisms of suitable categories, is put at work in describing weighted automata as coalgebras in such categories.
Some attention is paid to the interface between the index-free (categorial) language of matrix algebra and the corresponding index-wise, set-theoretic notation.Fundação para a Ciência e a Tecnologia (FCT