Alejandro Sanchez

A language for behavioural modelling of architectural patterns

The complexity of interactions governing the coordination of loosely-coupled services, which forms the core of current software, brought behavioural issues up to the front of architectural concerns. This paper takes such a challenge seriously by lifting typical behaviour modelling techniques to the specification of both types and instances of architectural patterns in which the later ones are connected by ports that behave according to a water flow metaphor. A specific language is introduced for this purpose as well as a translator to mCRL2 so that the simulation and analysis techniques available in the corresponding toolset can be used to reason about (the behavioural layer of) software architectures. The approach is illustrated in a few examples.

A perspective on architectural re-engineering

Continuous evolution towards very large, heterogeneous, highly dynamic computing systems entails the need for sound and flexible approaches to deal with system modification and re-engineering. The approach proposed in this paper combines an analysis stage, to identify concrete patterns of interaction in legacy code, with an iterative re-engineering process at a higher level of abstraction. Both stages are supported by the tools CoordPat and Archery, respectively. Bi-directional model transformations connecting code level and design level architectural models are defined. The approach is demonstrated in a (fragment of a) case study.

Analysing Tactics in Architectural Patterns

This paper presents an approach to analyse the application of tactics in architectural patterns. We define and illustrate the approach using ARCHERY, a language for specifying, analysing and verifying architectural patterns. The approach consists of characterising the design principles of an architectural pattern as constraints, expressed in the language, and then, establishing a refinement relation based on their satisfaction. The application of tactics preserving refinement ensures that the original design principles, expressed themselves as constraints, still hold in the resulting architectural pattern. The paper focuses on fault-tolerance tactics, and identifies a set of requirements for a semantic framework characterising them. The application of tactics represented as model transformations is then discussed and illustrated using two case studies.

Specifying structural constraints of architectural patterns in the ARCHERY language

ARCHERY is an architectural description language for modelling and reasoning about distributed, heterogeneous and dynamically reconfigurable systems in terms of architectural patterns. The language supports the specification of architectures and their reconfiguration. This paper introduces a language extension for precisely describing the structural design decisions that pattern instances must respect in their (re)configurations. The extension is a propositional modal logic with recursion and nominals referencing components, i.e., a hybrid µ-calculus. Its expressiveness allows specifying safety and liveness constraints, as well as paths and cycles over structures. Refinements of classic architectural patterns are specified.

On the verification of architectural reconfigurations

In a reconfigurable system, the response to contextual or internal change may trigger reconfiguration events which, on their turn, activate scripts that change the systems architecture at runtime. To be safe, however, such reconfigurations are expected to obey the fundamental principles originally specified by its architect. This paper introduces an approach to ensure that such principles are observed along reconfigurations by verifying them against concrete specifications in a suitable logic. Architectures, reconfiguration scripts, and principles are specified in Archery, an architectural description language with formal semantics. Principles are encoded as constraints, which become formulas of a two-layer graded hybrid logic, where the upper layer restricts reconfigurations, and the lower layer constrains the resulting configurations. Constraints are verified by translating them into logic formulas, which are interpreted over models derived from Archery specifications of architectures and reconfigurations. Suitable notions of bisimulation and refinement, to which the architect may resort to compare configurations, are given, and their relationship with modal validity is discussed. HighlightsDescribes approach to ensure fundamental principles of a system in reconfigurations.Specifies principles as constraints in an architectural description language.Translates constraints into a two-layer graded hybrid logic.Derives interpretation models from specifications of architectures and reconfigurations.Provides equivalence and refinement notions to compare reconfigurations.

Modelling and Verifying Smell-Free Architectures with the Archery Language

Architectural (bad) smells are design decisions found in software architectures that degrade the ability of systems to evolve. This paper presents an approach to verify that a software architecture is smell-free using the Archery architectural description language. The language provides a core for modelling software architectures and an extension for specifying constraints. The approach consists in precisely specifying architectural smells as constraints, and then verifying that software architectures do not satisfy any of them. The constraint language is based on a propositional modal logic with recursion that includes: a converse operator for relations among architectural concepts, graded modalities for describing the cardinality in such relations, and nominals referencing architectural elements. Four architectural smells illustrate the approach.

Verifying Bigraphical Models of Architectural Reconfigurations

ARCHERY is an architectural description language for modelling and reasoning about distributed, heterogeneous and dynamically reconfigurable systems. This paper proposes a structural semantics for ARCHERY, and a method for deriving labelled transition systems (LTS) in which states and transitions represent configurations and reconfiguration operations, respectively. Architectures are modelled by bigraphs and their dynamics by parametric reaction rules. The resulting LTSs can be regarded as Kripke frames, appropriate for verifying reconfiguration constraints over architectural patterns expressed in a modal logic. The derivation method proposed here applies the approach in [1] twice, and combines the results of each application to obtain a label representing a reconfiguration operation and its actual parameters. Labels obtained in this way are minimal and yield LTSs in which bisimulation is a congruence.