Mieke Massink

Towards a Formal Operational Semantics of UML Statechart Diagrams

Statechart Diagrams are a notation for describing behaviours in the framework of UML, the Unified Modeling Language of object-oriented systems. UML is a semi-formal language, with a precisely defined syntax and static semantics but with an only informally specified dynamic semantics. UML Statechart Diagrams differ from classical statecharts, as defined by Harel, for which formalizations and results are available in the literature. This paper sets the basis for the development of a formal semantics for UML Statechart Diagrams based on Kripke structures. This forms the first step towards model checking of UML Statechart Diagrams. We follow the approach proposed by Mikk and others: we first map Statechart Diagrams to the intermediate format of extended hierarchical automata and then we define an operational semantics for these automata. We prove a number of properties of such semantics which reflect the design choices of UML Statechart Diagrams.

AGILE: Software Architecture for Mobility.

Architecture-based approaches have been promoted as a means of controlling the complexity of system construction and evolution, in particular for providing systems with the agility required to operate in turbulent environments and to adapt very quickly to changes in the enterprise world. Recent technological advances in communication and distribution have made mobility an additional factor of complexity, one for which current architectural concepts and techniques can be hardly used. The AGILE project is developing an architectural approach in which mobility aspects can be modelled explicitly and mapped on the distribution and communication topology made available at physical levels. The whole approach is developed over a uniform mathematical framework based on graph-oriented techniques that support sound methodological principles, formal analysis, and refinement. This paper describes the AGILE project and some of the results gained during the first project year.

Automatic verification of a lip-synchronisation protocol using Uppaal

Abstract. We present the formal specification and verification of a lip-synchronisation protocol using the real-time model checker Uppaal. A number of specifications of this protocol can be found in the literature, but this is the first automatic verification. We take a published specification of the protocol, code it up in the Uppaal timed automata notation and then verify whether the protocol satisfies the key properties of jitter and skew. The verification reveals some aws in the protocol. In particular, it shows that for certain sound and video streams the protocol can time-lock before reaching a prescribed error state. We also discuss our experience with Uppaal, with particular reference to modelling timeouts and to deadlock analysis.

Model checking dependability attributes of wireless group communication

Models used for the analysis of dependability and performance attributes of communication protocols often abstract considerably from the details of the actual protocol. These models often consist of concurrent sub-models and this may make it hard to judge whether their behaviour is faithfully reflecting the protocol. In this paper, we show how model checking of continuous-time Markov chains, generated from high-level specifications, facilitates the analysis of both correctness and dependability attributes. We illustrate this by revisiting a dependability analysis as stated in A. Coccoli et al. (2001)of a variant of the central access protocol of the IEEE 802.11 standard for wireless local area networks. This variant has been developed to support real-time group communication between autonomous mobile stations. Correctness and dependability properties are formally characterised using continuous stochastic logic and are automatically verified by the ETMCC model checker. The models used are specified as stochastic activity nets.

Basic Observables for Probabilistic May Testing

Probabilistic models are widely used to analyze embedded, networked, and more recently biological systems. Existing numerical analysis techniques are limited to finite- state models and suffer from the state explosion problem. As a consequence, the user often has to manually abstract the intended model to get a tractable one. To this end, we propose the predicate abstraction model checker PASS which automates this process. We leverage recent advances in automatic theorem proving to compute tractable finite-state models. Experiments show the feasibility of our approach. To the best of our knowledge, this is the first time that properties of probabilistic infinite-state models have been verified at this level of automation.The definition of behavioural preorders over process terms as the maximal (pre-)congruences induced by basic observables has proven to be a useful technique to define various preorders and equivalences in the non-probabilistic setting. In this paper, we consider probabilistic observables to define an observational semantics for a probabilistic process calculus. The resulting pre-congruence is proven to coincide with a probabilistic may preorder, which, in turn, corresponds to a natural probabilistic extension of the may testing preorder of De Nicola and Hennessy.

Towards model checking stochastic aspects of the thinkteam user interface

Stochastic model checking is a recent extension of traditional model-checking techniques for the integrated analysis of both qualitative and quantitative system properties. In this paper we show how stochastic model checking can be conveniently used to address a number of usability concerns that involve quantitative aspects of a user interface for the industrial groupware system thinkteam. thinkteam is a ready-to-use Product Data Management application developed by think3. It allows enterprises to capture, organise, automate, and share engineering product information and it is an example of an asynchronous and dispersed groupware system. Several aspects of the functional correctness, such as concurrency aspects and awareness aspects, of the groupware protocol underlying thinkteam and of its planned publish/subscribe notification service have been addressed in previous work by means of a traditional model-checking approach. In this paper we investigate the trade-off between two different design options for granting users access to files in the database: a retrial approach and a waiting-list approach and show how stochastic model checking can be used for such analyses.

Analysis of pointing tasks on a white board

We study the variations in two dimensional (2D) pointing tasks on a traditional white board of a group of subjects by means of capturing their movement traces in an automatic way with the Mimio device. Such traces provide detailed insight in the variability of 2D pointing relevant for example for the design of computer vision based gestural interaction. This study provides experimental evidence that for medium large distances Fitts model, and Welfords and Shannons variants, continue to show a linear relationship between movement time (MT) and the index of difficulty (ID) with a high correlation for the ranges considered. The expected increased sensitivity to changes in ID for these larger distances are confirmed. Nearly all movements show three phases: a planning phase, a ballistic phase and an adjustment phase. Finally, we show that the arrival time at the target resembles a log-normal distribution.

Investigating the Behaviour of PREMO Synchronizable Objects

PREMO stands for Presentation Environment for Multimedia Objects and is a major new standard under development within ISO/IEC. It addresses the creation of, presentation of and interaction with all forms of information using single or multiple media. The standard (u. d.) is currently developed using an Object Oriented approach. Such a state based specification, however, does not support conveniently the analysis of the temporal relationships occurring among operations. In this paper we model PREMO synchronizable objects defined in the standard as processes in the standardized process algebra Lotos. The approach we follow is a new way to obtain a specification in a constraint oriented style and is inspired by the Object Oriented approach. We let methods correspond to actions and values of control variables with processes. Each process consists of actions that are enabled for the value of the control variable that is modelled by the process. This style leads to Basic Lotos specifications that are directly suitable for computer assisted analysis such as model checking and simulation.

Modelling and Verification of PREMO Synchronisable Objects

Abstract. The PREMO standard, Presentation Environment for Multimedia Objects, is a major new standard under development within ISO/IEC. It addresses the creation of, presentation of, and interaction with all forms of information using single or multiple media. In this paper we give a formal LOTOS specification, amenable to automatic verification, of the PREMO synchronisable object, which is one of the central parts of the standard. Various design options are investigated by a combination of constraint oriented specification and model checking. This shows the usefulness of formal specification and automatic verification during the design phase of an international standard.