Person:
Gregorio Rodríguez, Carlos

First Name

Carlos

Last Name

Gregorio Rodríguez

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Estudios estadísticos

Department

Sistemas Informáticos y Computación

Area

Lenguajes y Sistemas Informáticos

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Now showing 1 - 10 of 22

On the unification of process semantics: equational semantics
(Elsevier, 2009-08) Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Palomino, Miguel
The complexity of parallel systems has produced a large collection of semantics for processes, a classification of which is provided by Van Glabbeek's linear time-branching time spectrum; however, no suitable unified definitions were available. We have discovered the way to unify them, both in an observational framework and by means of a quite small set of parameterized (in)equations that provide a sound and complete axiomatization of the preorders that define them. In more detail, we have proved that we only need a generic simulation axiom (NS), which defines the family of constrained simulation semantics, thus covering the class of branching time semantics, and a generic axiom (ND) for reducing the non-determinism of processes, by means of which we introduce the additional identifications induced by each of the linear time semantics.
(Bi)simulations up-to characterise process semantics
(Elsevier Science, 2009-02) Frutos Escrig, David de; Gregorio Rodríguez, Carlos
We define (bi)simulations up-to a preorder and show how we can use them to provide a coinductive, (bi)simulation-like, characterisation of semantic (equivalences) preorders for processes. In particular, we can apply our results to all the semantics in the linear time-branching time spectrum that are defined by preorders coarser than the ready simulation preorder. The relation between bisimulations up-to and simulations up-to allows us to find some new relations between the equivalences that define the semantics and the corresponding preorders. In particular, we have shown that the simulation up-to an equivalence relation is a canonical preorder whose kernel is the given equivalence relation. Since all of these canonical preorders are defined in an homogeneous way, we can prove properties for them in a generic way. As an illustrative example of this technique, we generate an axiomatic characterisation of each of these canonical preorders, that is obtained simply by adding a single axiom to the axiomatization of the original equivalence relation. Thus we provide an alternative axiomatization for any axiomatizable preorder in the linear time-branching time spectrum, whose correctness and completeness can be proved once and for all. Although we first prove, by induction, our results for finite processes, then we see, by using continuity arguments, that they are also valid for infinite (finitary) processes.
Coinductive Characterisations Reveal Nice Relations Between Preorders and Equivalences
(Elsevier, 2008-04) Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Palomino, Miguel
There are two ways to define a semantics for process algebras: either directly by means of an equivalence relation or by means of a preorder whose kernel is the desired equivalence. We are interested in the relationship between these two presentations. Using our characterisation of the behaviour preorders by means of simulations up-to we were able to generate the canonical preorders corresponding to each behaviour equivalence. The axiomatizations of these preorders can be obtained by adding to the axioms of the equivalence that of the appropriate simulation. Aceto, Fokkink and Ingólfsdóttir have presented an algorithm that goes in the opposite direction, constructing an axiomatization of the induced equivalence from that of a given preorder. Following a different path we were able to get a correct proof and an enhanced algorithm. In this paper we present an shorter and simpler proof of this result, based on our coinductive characterisations of the behaviour preorders, and in particular in the existence of the canonical preorders. More important, we also present further generalisations of the result, since our coinductive characterisations are not only valid for the semantics coarser than the ready simulation. By means of these new proofs and results we hope to contribute to a better knowledge of the semantics of processes and to better understand the tight relations between preorders and equivalences that define them.
Unifying the linear time-branching time spectrum of strong process semantics
(Tech Univ Braunschweig, Inst Theoretical Computer Sci, 2013) Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Palomino, Miguel; Romero Hernández, David
Van Glabbeek's linear time-branching time spectrum is one of the most relevant work on comparative study on process semantics, in which semantics are partially ordered by their discrimination power. In this paper we bring forward a refinement of this classification and show how the process semantics can be dealt with in a uniform way: based on the very natural concept of constrained simulation we show how we can classify the spectrum in layers; for the families lying in the same layer we show how to obtain in a generic way equational, observational, logical and operational characterizations; relations among layers are also very natural and differences just stem from the constraint imposed on the simulations that rule the layers. Our methodology also shows how to achieve a uniform treatment of semantic preorders and equivalences.
Simulations up-to and canonical preorders
(Elsevier, 2007) Frutos Escrig, David de; Gregorio Rodríguez, Carlos
In this paper we define simulations up-to a preorder and show how we can use them to provide a coinductive, simulation-like, characterization of semantic preorders for processes. The result applies to a wide class of preorders, in particular to all semantic preorders coarser than the ready simulation preorder in the linear time-branching time spectrum. An interesting but unexpected result is that, when built from an equivalence relation, the simulation up-to is a canonical preorder whose kernel is the given equivalence relation. These canonical preorders have several nice properties, the main being that since all of them are defined in a homogeneous way, their properties can be proved in a generic way. In particular, we present an axiomatic characterization of each of these canonical preorders, that is obtained just by adding a single axiom to the axiomatization of the original equivalence relation. This gives us an alternative axiomatization for every axiomatizable preorder in the linear time-branching time spectrum, whose correctness and completeness can be proved once and for all.
Process equivalences as global bisimulations
(Graz Univ. Technolgoy, Inst. Information Systems Computer Med., 2006) Frutos Escrig, David de; Gregorio Rodríguez, Carlos
Bisimulation can be defined in a simple way using coinductive methods, and has rather pleasant properties. Ready similarity was proposed by Meyer et al. as a way to weakening the bisimulation equivalence thus getting a semantics defined in a similar way, but supported for more reasonable (weaker) observational properties. Global bisimulations were introduced by Frutos et al. in order to study different variants of non-determinism getting, in particular, a semantics under which the internal choice operator becomes associative. Global bisimulations are defined as plain bisimulations but allowing the use of new moves, called global transitions, that can change the processes not only locally in its head, but anywhere. Now we are continuing the study of global bisimulation but focusing on the way different semantics can be characterised as global bisimulation semantics. In particular, we have studied ready similarity, on the one hand because it was proposed as the strongest reasonable semantics weaker than bisimulation; on the other hand, because ready similarity was not directly defined as an equivalence relation but as the nucleus of an order relation, and this open the question whether it is also possible to define it as a symmetric bisimulation-like semantics. We have got a simple and elegant characterisation of ready similarity as a global bisimulation semantics, that provides a direct symmetric characterisation of it as an equivalence relation, without using any order as intermediate concept. Besides, we have found that it is not necessary to start from a simulation based semantics to get an equivalent global bisimulation. What has proved to be very useful is the axiomatic characterization of the semantics. Following these ideas we have got also global bisimulation for several semantics, including refusals and traces. That provides a general framework that allows to relate both intensional and extensional semantics.
Axiomatizing weak simulation semantics over BCCSP
(Elsevier, 2014-06-05) Aceto, Luca; Frutos Escrig, David de; Gregorio Rodríguez, Carlos
This paper is devoted to the study of the (in)equational theory of the largest (pre)congruences over the language BCCSP induced by variations on the classic simulation preorder and equivalence that abstract from internal steps in process behaviours. In particular, the article focuses on the (pre)congruences associated with the weak simulation, the weak complete simulation and the weak ready simulation preorders. We present results on the (non)existence of finite (ground-)complete (in)equational axiomatizations for each of these behavioural semantics. The axiomatization of those semantics using conditional equations is also discussed in some detail.
Ready to preorder: an algebraic and general proof
(Elsevier, 2009) Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Palomino, Miguel
There have been quite a few proposals for behavioural equivalences for concurrent processes, and many of them are presented in Van Glabbeek’s linear time-branching time spectrum. Since their original definitions are based on rather different ideas, proving general properties of them all would seem to require a case-by-case study. However, the use of their axiomatizations allows a uniform treatment that might produce general proofs of those properties. Recently Aceto, Fokkink and Ingólfsdóttir have presented a very interesting result: for any process preorder coarser than the ready simulation in the linear time-branching time spectrum they show how to get an axiomatization of the induced equivalence. Unfortunately, their proof is not uniform and requires a case-by-case analysis. Following the algebraic approach suggested above, in this paper we present a much simpler proof of that result which, in addition, is more general and totally uniform, so that it does not need to consider one by one the different semantics in the spectrum.
On the unification of process semantics: observational semantics
(Springer, 2009) Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Palomino, Miguel; Nielsen, Mogens; Kucera, Antonin; Miltersen, Peter Bro; Palamidessi, Castuscia; Tuma, Petr; Valencia, Frank
The complexity of parallel systems has produced a large collection of semantics for processes. Van Glabbeek’s linear time-branching time spectrum provides a classification of most of these semantics; however, no suitable unified definitions were available. We have discovered how to unify them, both in an observational framework and in an equational framework. In this first part of our study we present the observational semantics, that stresses the differences between the simulation (branching) semantics and the extentional (linear) semantics. As a result we rediscover the classification in van Glabbeek’s spectrum and shed light on it, obtaining a framework where we can consider all the semantics in the spectrum at the same time. Also, we have discovered some “lost links” that correspond to semantics, possibly not too interesting (at the moment), that provide a clearer picture of the spectrum.
Axiomatizing Weak Ready Simulation Semantics over BCCSP
(Springer, 2011) Aceto, Luca; Frutos Escrig, David de; Gregorio Rodríguez, Carlos; Ingolfsdottir, Anna; Cerone, Antonio; Pihlajasaari, Pekka
Ready simulation has proven to be one of the most significant semantics in process theory. It is at the heart of a number of general results that pave the way to a comprehensive understanding of the spectrum of process semantics. Since its original definition by Bloom, Istrail and Meyer in 1995, several authors have proposed generalizations of ready simulation to deal with internal actions. However, a thorough study of the (non-)existence of finite (in)equational bases for weak ready simulation semantics is still missing in the literature. This paper presents a complete account of positive and negative results on the axiomatizability of weak ready simulation semantics over the language BCCSP. In addition, this study offers a thorough analysis of the axiomatizability properties of weak simulation semantics.