Papers by Alberto Lluch Lafuente
We present Architectural Design Rewriting (ADR), a graphbased approach to deal with the design of... more We present Architectural Design Rewriting (ADR), a graphbased approach to deal with the design of reconfigurable software architectures. The key features we promote are: (i) hierarchical design; (ii) soft constraints for modeling QoS attributes; (iii) style-preserving reconfigurations; (iv) rule-based approach; and (v) algebraic presentation. Roughly, actual architectures are modeled by graphs with port and attribute nodes through which component edges are connected. Uniformly, QoS constraints on attributes are also modeled as edges. Architectures are designed hierarchically by a set of edge replacement rules that fix the architectural style. Depending on their reading, productions allow: (i) top-down design by refinement, (ii) bottom-up typing, and (iii) algebraic composition of typed architectures, with terms corresponding to style proofs. Moreover, productions exploit constraint primitives that can be used in the refinement phase, e.g., to reserve a certain amount of resources or to postpone architectural decisions. Similarly, reconfigurations are modeled as graph transformations triggered by constraints primitives to guarantee that certain levels of QoS are mantained. The main contribution is showing that we can take advantage by exploiting styles when specifying reconfigurations: (i) by giving hierarchical specifications that exploit the classes introduced by the style, (ii) by guaranteeing that all reconfigurations are style-preserving, (iii) by expressing reconfigurations as ordinary term rewrite rules on the algebra of style proofs. Overall, this results in a simple and formal mechanism for designing architectures according to a style, for checking that an architecture is an instance of a style and for ensuring style preservation during reconfigurations.
Bulletin of the …, 2008
Architectural Design Rewriting (ADR) is a declarative rule-based approach for the design of dynam... more Architectural Design Rewriting (ADR) is a declarative rule-based approach for the design of dynamic software architectures. The key features that make ADR a suitable and expressive framework are the algebraic presentation of graph-based structures and the use of conditional rewrite rules. These features enable the modelling of, e.g. hierarchical design, inductively defined reconfigurations and ordinary computation. Here, we promote ADR as an Architectural Description Language.
We present an approach for the verification of spatial properties with Spin. We first extend one ... more We present an approach for the verification of spatial properties with Spin. We first extend one of Spin’s main property specification mechanisms, i.e., the linear-time temporal logic LTL, with spatial connectives that allow us to restrict the reasoning of the behaviour of a system to some components of the system, only. For instance, one can express whether the system can reach a certain state from which a subset of processes can evolve alone until some property is fulfilled. We give a model checking algorithm for the logic and propose how Spin can be minimally extended to include the algorithm. We also discuss potential improvements to mitigate the exponential complexity introduced by spatial connectives. Finally, we present some experiments that compare our Spin extension with a spatial model checker for the π-calculus.
Electronic Communication of The European Association of Software Science and Technology, 2011
We present our prototypical tool for the verification of graph transformation systems. The major ... more We present our prototypical tool for the verification of graph transformation systems. The major novelty of our tool is that it provides a model checker for temporal graph properties based on counterpart semantics for quantified µ-calculi. Our tool can be considered as an instantiation of our approach to counterpart semantics which allows for a neat handling of creation, deletion and merging in systems with dynamic structure. Our implementation is based on the object-based machinery of Maude, which provides the basics to deal with attributed graphs. Graph transformation systems are specified with term rewrite rules. The model checker evaluates logical formulae of second-order modal µ-calculus in the automatically generated Counterpart Model (a sort of unfolded graph transition system) of the graph transformation system under study. The result of evaluating a formula is a set of assignments for each state, associating node variables to actual nodes.
Electronic Notes in Theoretical Computer Science, 2009
Under several regards, various of the recently proposed computational paradigms are open-ended, i... more Under several regards, various of the recently proposed computational paradigms are open-ended, i.e. they may comprise components whose behaviour is not or cannot be fully specified. For instance, applications can be distributed across different administration domains that do not fully disclose their internal business processes to each other, or the dynamics of the system may allow reconfigurations and dynamic bindings whose specification is not available at design time. While a large set of mature design and analysis techniques for closed systems have been developed, their lifting to the open case is not always straightforward. Some existing approaches in the process calculi community are based on the need of proving properties for components that may hold in any, or significantly many, execution environments. Dually, frameworks describing the dynamics of systems with unspecified components have also been presented. In this paper we lay some preliminary ideas on how to extend a symbolic semantics model for open systems in order to deal with name-based calculi. Moreover, we also discuss how the use of a simple type system based on name-decoration for unknown components can improve the expressiveness of the framework. The approach is illustrated on a simple, paradigmatic calculus of web crawlers, which can be understood as a term representation of a simple class of graphs.
We propose a novel approach to the semantics of quantified μ-calculi, considering models where st... more We propose a novel approach to the semantics of quantified μ-calculi, considering models where states are algebras; the evolution relation is given by a counterpart relation (a family of partial homomorphisms), allowing for the creation, deletion, and merging of components; and formulas are interpreted over sets of state assignments (families of substitutions, associating formula variables to state components). Our proposal avoids the limitations of existing approaches, usually enforcing restrictions of the evolution relation: the resulting semantics is a streamlined and intuitively appealing one, yet it is general enough to cover most of the alternative proposals we are aware of.
… Approaches to Software …, 2012
In this position paper we present a conceptual vision of adaptation, a key feature of autonomic s... more In this position paper we present a conceptual vision of adaptation, a key feature of autonomic systems. We put some stress on the role of control data and argue how some of the programming paradigms and models used for adaptive systems match with our conceptual framework.
Lecture Notes in Computer Science, 2011
We present our approach to the denotation and representation of hierarchical graphs: a suitable a... more We present our approach to the denotation and representation of hierarchical graphs: a suitable algebra of hierarchical graphs and two domains of interpretations. Each domain of interpretation focuses on a particular perspective of the graph hierarchy: the top view (nested boxes) is based on a notion of embedded graphs while the side view (tree hierarchy) is based on gs-graphs. Our algebra can be understood as a high-level language for describing such graphical models, which are well suited for defining graphical representations of service-oriented systems where nesting (e.g. sessions, transactions, locations) and linking (e.g. shared channels, resources, names) are key aspects.
Rule-based specifications have been very successful as a declarative approach in many domains, du... more Rule-based specifications have been very successful as a declarative approach in many domains, due to the handy yet solid foundations offered by rule-based machineries like term and graph rewriting. Realistic problems, however, call for suitable techniques to guarantee scalability. For instance, many domains exhibit a hierarchical structure that can be exploited conveniently. This is particularly evident for composition associations of models. We propose an explicit representation of such structured models and a methodology that exploits it for the description and analysis of model- and rule-based systems. The approach is presented in the framework of rewriting logic and its efficient implementation in the rewrite engine Maude and is illustrated with a case study.
Lecture Notes in Computer Science, 2011
Architectural Design Rewriting (ADR) is an approach for the design of software architectures deve... more Architectural Design Rewriting (ADR) is an approach for the design of software architectures developed within Sensoria by reconciling graph transformation and process calculi techniques. The key feature that makes ADR a suitable and expressive framework is the algebraic handling of structured graphs, which improves the support for specification, analysis and verification of service-oriented architectures and applications. We show how ADR is used as a formal ground for high-level modelling languages and approaches developed within Sensoria.
We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism... more We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism: two terms are equated exactly when they represent the same graph. Our algebra can be understood as a high-level language for describing graphs with a node-sharing, embedding structure, and it is then well suited for defining graphical representations of software models where nesting and linking are key aspects.
Electronic Notes in Theoretical Computer Science, 2006
The paper introduces a novel approach to the verification of spatial properties for finite π-calc... more The paper introduces a novel approach to the verification of spatial properties for finite π-calculus specifications. The mechanism is based on a recently proposed graphical encoding for mobile calculi: Each process is mapped into a (ranked) graph, such that the denotation is fully abstract with respect to the usual structural congruence (i.e., two processes are equivalent exactly when the corresponding encodings yield the same graph). Spatial properties for reasoning about the behavior and the structure of π-calculus processes are then expressed in a logic introduced by Caires, and they are verified on the graphical encoding of a process, rather than on its textual representation. More precisely, the graphical presentation allows for providing a simple and easy to implement verification algorithm based on the graphical encoding (returning true if and only if a given process verifies a given spatial formula).
We propose a sound and complete axiomatisation of a class of graphs with nesting and either local... more We propose a sound and complete axiomatisation of a class of graphs with nesting and either locally or globally restricted nodes. Such graphs allow to represent explicitly and at the right level of abstraction some relevant topological and logical features of models and systems, including nesting, hierarchies, sharing of resources, and pointers or links. We also provide an encoding of the proposed algebra into terms of a gs-monoidal theory, and through these into a suitable class of ”wellscoped” term graphs, showing that this encoding is sound and complete with respect to the axioms of the algebra.
We present a UML Profile for the description of service oriented applications. The profile focuse... more We present a UML Profile for the description of service oriented applications. The profile focuses on style-based design and reconfiguration aspects at the architectural level. Moreover, it has formal support in terms of an approach called Architectural Design Rewriting, which enables formal analysis of the UML specifications. We show how our prototypical implementation can be used to analyse and verify properties of a service oriented application.
Graphs are suitable modeling formalisms for software and hardware systems involving aspects such ... more Graphs are suitable modeling formalisms for software and hardware systems involving aspects such as communication, object orientation, concurrency, mobility and distribution. State spaces of such systems can be represented by graph transition systems, which are basically transition systems whose states and transitions represent graphs and graph morphisms. In this paper, we propose the modeling of graph transition systems in PDDL and the application of heuristic search planning for their analysis. We consider different heuristics and present experimental results.
This paper extends our graph-based approach to the verification of spatial properties of π-calcul... more This paper extends our graph-based approach to the verification of spatial properties of π-calculus specifications. The mechanism is based on an encoding for mobile calculi where each process is mapped into a graph (with interfaces) such that the denotation is fully abstract with respect to the usual structural congruence, i.e., two processes are equivalent exactly when the corresponding encodings yield isomorphic graphs. Behavioral and structural properties of π-calculus processes expressed in a spatial logic can then be verified on the graphical encoding of a process rather than on its textual representation. In this paper we introduce a modal logic for graphs and define a translation of spatial formulae such that a process verifies a spatial formula exactly when its graphical representation verifies the translated modal graph formula.
Graphs are suitable modeling formalisms for software and hardware systems involving aspects such ... more Graphs are suitable modeling formalisms for software and hardware systems involving aspects such as communication, object orientation, concurrency, mobility and distribution. State spaces of such systems can be represented by graph transition systems, which are basically transition systems whose states and transitions represent graphs and graph morphisms. Heuristic search is a successful Artificial Intelligence technique for solving exploration problems implicitly present in games, planning, and formal verification. Heuristic search exploits information about the problem being solved to guide the exploration process. The main benefits are significant reductions in the search effort and the size of solutions. We propose the application of heuristic search for the analysis of graph transition systems. We define algorithms and heuristics and present experimental results.
We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism... more We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism: two terms are equated exactly when they represent the same graph. Our algebra can be understood as a high-level language for describing graphs with a node-sharing, embedding structure, and it is then well suited for defining graphical representations of software models where nesting and linking are key aspects. In particular, we propose the use of our graph formalism as a convenient way to describe configurations in process calculi equipped with inherently hierarchical features such as sessions, locations, transactions, membranes or ambients. The graph syntax can be seen as an intermediate representation language, that facilitates the encodings of algebraic specifications, since it provides primitives for nesting, name restriction and parallel composition. In addition, proving soundness and correctness of an encoding (i.e. proving that structurally equivalent processes are mapped to isomorphic graphs) becomes easier as it can be done by induction over the graph syntax.
Abstract: This paper extends the invited talk by the first author about the virtues of structured... more Abstract: This paper extends the invited talk by the first author about the virtues of structured graphs. The motivation behind the talk and this paper relies on our experience on the development of ADR, a formal approach for the design of style-conformant, reconfigurable software ...
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Papers by Alberto Lluch Lafuente