Constraints for behavioural specifications

Behavioural specifications with constraints for the incremental development of algebraic specifications are presented. The behavioural constraints correspond to the completely defined subparts of a given incomplete behavioural specification. Moreover, the local observability criteria used within a behavioural constraint could not coincide with the global criteria used in the behavioural specification. This is absolutely needed because, otherwise, some constraints could involve only non observable sorts and therefore have trivial semantics. Finally, the extension operations and completion operations for refining specifications are defined. The extension operations correspond to horizontal refinements and build larger specifications on top of existing ones in a conservative way. The completion operations correspond to vertical refinements, they add detail to an incomplete behavioural specification and they do restrict the class of models.Postprint (published version

Interestingness of traces in declarative process mining: The janus LTLPf Approach

Declarative process mining is the set of techniques aimed at extracting behavioural constraints from event logs. These constraints are inherently of a reactive nature, in that their activation restricts the occurrence of other activities. In this way, they are prone to the principle of ex falso quod libet: they can be satisfied even when not activated. As a consequence, constraints can be mined that are hardly interesting to users or even potentially misleading. In this paper, we build on the observation that users typically read and write temporal constraints as if-statements with an explicit indication of the activation condition. Our approach is called Janus, because it permits the specification and verification of reactive constraints that, upon activation, look forward into the future and backwards into the past of a trace. Reactive constraints are expressed using Linear-time Temporal Logic with Past on Finite Traces (LTLp f). To mine them out of event logs, we devise a time bi-directional valuation technique based on triplets of automata operating in an on-line fashion. Our solution proves efficient, being at most quadratic w.r.t. trace length, and effective in recognising interestingness of discovered constraints

Visual Specification Patterns

Visual modelling notations such as constraint diagrams can be used for the behavioural specifications of software components. This includes specifying invariants on classes or types and preconditions and postconditions of operations. However, one current problem in specifying components comes from the fact that editing constraints manually is time consuming and error prone and so we may adopt a pattern-based approach to alleviate this problem. One way to simplify the definition of constraints is to identify and capture those recurring constraints in the form of visual specification patterns. Such patterns would facilitate the automatic generation of diagrammatic constraints. This paper identifies some specification patterns that frequently occur when specifying software components and provides a diagrammatic representation of these patterns. This will form the basis of a library of specification patterns that could be used in the context of tools. We also show how such patterns can be combined in order to specify more complex constraints

Macroeconomic Adjustment and Foreign Trade of Centrally Planned Economies

This empirical study stresses the underlying macroeconomic forces which determine foreign trade flows in CPEs. The general specification includes a planners' demand equation for the volume of imports, a planners' supply equation for the volume of exports, and a rest-of-world demand equation for the export price level. The planners' behavioural equations include variables for activity levels, trade balance constraints, prices, and domestic excess demand. The import price is exogenous. This simultaneous equation model is estimated on annual data from the mid-1950s to the mid-1970s, for Czechoslovakia, the GDR, Hungary, and Poland. Maximum likelihood estimation in a nested hypothesis testing framework allows selection of restricted versions of the general model for each country. Estimated price elasticities accord with the underlying theory, and the excess demand variables perform well.

A monitoring approach for runtime service discovery

Effective runtime service discovery requires identification of services based on different service characteristics such as structural, behavioural, quality, and contextual characteristics. However, current service registries guarantee services described in terms of structural and sometimes quality characteristics and, therefore, it is not always possible to assume that services in them will have all the characteristics required for effective service discovery. In this paper, we describe a monitor-based runtime service discovery framework called MoRSeD. The framework supports service discovery in both push and pull modes of query execution. The push mode of query execution is performed in parallel to the execution of a service-based system, in a proactive way. Both types of queries are specified in a query language called SerDiQueL that allows the representation of structural, behavioral, quality, and contextual conditions of services to be identified. The framework uses a monitor component to verify if behavioral and contextual conditions in the queries can be satisfied by services, based on translations of these conditions into properties represented in event calculus, and verification of the satisfiability of these properties against services. The monitor is also used to support identification that services participating in a service-based system are unavailable, and identification of changes in the behavioral and contextual characteristics of the services. A prototype implementation of the framework has been developed. The framework has been evaluated in terms of comparison of its performance when using and when not using the monitor component

Ontology-based modelling of architectural styles

The conceptual modelling of software architectures is of central importance for the quality of a software system. A rich modelling language is required to integrate the different aspects of architecture modelling, such as architectural styles, structural and behavioural modelling, into a coherent framework. Architectural styles are often neglected in software architectures. We propose an ontological approach for architectural style modelling based on description logic as an abstract, meta-level modelling instrument. We introduce a framework for style definition and style combination. The application of the ontological framework in the form of an integration into existing architectural description notations is illustrated

Clafer: Lightweight Modeling of Structure, Behaviour, and Variability

Embedded software is growing fast in size and complexity, leading to intimate mixture of complex architectures and complex control. Consequently, software specification requires modeling both structures and behaviour of systems. Unfortunately, existing languages do not integrate these aspects well, usually prioritizing one of them. It is common to develop a separate language for each of these facets. In this paper, we contribute Clafer: a small language that attempts to tackle this challenge. It combines rich structural modeling with state of the art behavioural formalisms. We are not aware of any other modeling language that seamlessly combines these facets common to system and software modeling. We show how Clafer, in a single unified syntax and semantics, allows capturing feature models (variability), component models, discrete control models (automata) and variability encompassing all these aspects. The language is built on top of first order logic with quantifiers over basic entities (for modeling structures) combined with linear temporal logic (for modeling behaviour). On top of this semantic foundation we build a simple but expressive syntax, enriched with carefully selected syntactic expansions that cover hierarchical modeling, associations, automata, scenarios, and Dwyer's property patterns. We evaluate Clafer using a power window case study, and comparing it against other notations that substantially overlap with its scope (SysML, AADL, Temporal OCL and Live Sequence Charts), discussing benefits and perils of using a single notation for the purpose

Supporting process reuse in PROMENADE

Process reuse (the ability to construct new processes by assembling already built ones) and process harvesting (the ability to build generic processes that may be further reused, from existing ones) are two crucial issues in process technology. Both activities involve defining a set of mechanisms, like abstraction, adaptation, composition, etc. which are appropriate to achieve their goals. In this report, we define a general framework to process reuse and harvesting that proposes a complete set of mechanisms to deal with both activities. This general framework is particularized to the context of a process modelling language to model software processes, called PROMENADE. A definition of the identified reuse and harvesting mecha-nisms is proposed in the context of PROMENADE. Finally, two process reuse case studies which composes various reuse mechanisms are presented.Postprint (published version