Hanêne Ben-Abdallah

Syntactic Detection of Process Divergence and Non-local Choice inMessage Sequence Charts

Message Sequence Charts (MSCs) are increasingly used in software engineering methodologies and tools to capture, for instance, system requirements, test scenarios, and simulation traces. They have been standardized by ITU-T in Recommendation Z.120 [IT96]. However, various aspects of environment behavior remain underspecified in MSCs, e.g., the presence of resources for inter-process communication and the coordination of concurrent processes at points of control branching. Such underspecifications can result in ambiguities in an MSC specification and discrepancies between an MSC specification and its implementation. In this paper we characterize two consequences of harmful underspecifications: process divergence and non-local branching choice. We also present two syntax-based analysis algorithms that detect both problems.

Formally specified monitoring of temporal properties

We describe the Monitoring and Checking (MaC) framework which provides assurance on the correctness of an execution of a real-time system at runtime. Monitoring is performed based on a formal specification of system requirements. MaC bridges the gap between formal specification, which analyzes designs rather than implementations, and testing, which validates implementations but lacks formality. An important aspect of the framework is a clear separation between implementation-dependent description of monitored objects and high-level requirements specification. Another salient feature is automatic instrumentation of executable code. The paper presents an overview of the framework, languages to express monitoring scripts and requirements, and a prototype implementation of MaC targeted at systems implemented in Java.

Timing Constraints in Message Sequence Chart Specifications

When dealing with timing constraints, the Z.120 standard of Message Sequence Charts (MSCs) is still evolving along with several proposals. This paper first reviews proposed extensions of MSCs to describe timing constraints. Secondly, the paper describes an analysis technique for timing consistency in iterating and branching MSC specifications. The analysis extends efficient current techniques for timing analysis of MSCs with no loops nor branchings. Finally, the paper extends our syntactic analysis of process divergence to MSCs with timing constraints.

A Process Algebraic Approach to the Schedulability Analysisof Real-Time Systems

To engineer reliable real-time systems, it is desirable to detect timing anomalies early in the development process. However, there is little work addressing the problem of accurately predicting timing properties of real-time systems before implementations are developed. This paper describes an approach to the specification and schedulability analysis of real-time systems based on the timed process algebra ACSR-VP, which is an extension of ACSR with value-passing communication and dynamic priorities. Combined with the existing features of ACSR for representing time, synchronization and resource requirements, ACSR-VP is capable of specifying a variety of real-time systems with different scheduling disciplines in a modular fashion. Moreover, we can use VERSA, a toolkit we have developed for ACSR, to perform schedulability analysis on real-time systems specified in ACSR-VP automatically by checking for a certain bisimulation relation.

MESA: Support for Scenario-Based Design of Concurrent Systems

The latest ITU-T standard syntax of Message Sequence Charts (MSCs) [16] offers several operators to compose MSCs in a hierarchical, iterating, and nondeterministic way. However, current tools operate on MSCs that describe finite, deterministic behavior. In this paper, we describe the architecture and the partial implementation of MESA, an MSC-based tool that supports early phases of the software development cycle. The main functionalities of MESA are: an environment for the composition of system models through MSCs, syntactic and model-based analysis of an MSC model, and resolution of resource related underspecifications in an MSC model.

Functional Size of Use Case Diagrams: A Fine-Grain Measurement

Software functional size (FS) prediction early in its lifecycle is vital for software project management. Such prediction requires the definition of software measures in terms of the specification and/or design language concepts. Within this context, several researchers have projected COSMIC functional size measures (FSM) onto various UML diagrams. However, these projections treated the diagrams separately despite their syntactic and semantic overlap within a model. In this paper, we present a fine-grain measurement for the UML use case diagram. Being a central diagram for models derived through the Unified Process, the use case diagram is implicitly related to all other diagrams. Thus, the detailed measurement of this diagram provides a reference measurement standard for other UML diagrams, e.g., the sequence and class diagrams.

Specification and analysis of real-time systems with PARAGON

This paper describes a methodology for the specification and analysis of distributed real-time systems using the toolset called PARAGON. PARAGON is based on the Communicating Shared Resources paradigm, which allows a real-time system to be modeled as a set of communicating processes that compete for shared resources. PARAGON supports both visual and textual languages for describing real-time systems. It offers automatic analysis based on state space exploration as well as user-directed simulation. Our experience with using PARAGON in several case studies resulted in a methodology that includes design patterns and abstraction heuristics, as well as an overall process. This paper briefly overviews the communicating shared resource paradigm and its toolset PARAGON, including the textual and visual specification languages. The paper then describes our methodology with special emphasis on heuristics that can be used in PARAGON to reduce the state space. To illustrate the methodology, we use examples from a real-life system case study.

A graphical language with formal semantics for the specification and analysis of real-time systems

Graphical communicating shared resources, GCSR, is a formal language for the specification and analysis of real-time systems including their functional and resource requirements. GCSR allows a modular and hierarchical, and thus, scalable specification of a real-time system. GCSR supports notions of communication through events, interrupt, concurrency, and time to describe a real-time system. In addition, GCSR allows the explicit representation of resources and priorities to arbitrate resource contention in a natural way that produces easy to understand and modify specifications. The semantics of GCSR is the algebra of communicating shared resources, a timed process algebra with operational semantics. The process algebra provides behavioral equivalence relations which can be used to verify the correctness of one GCSR specification with respect to the other.

A novel approach for off-line Arabic writer identification based on stroke feature combination

This paper presents a novel approach for off-line text-independent Arabic writer identification. The approach operates in four steps: 1) handwritten text is segmented into strokes after an image thinning step; 2)length, height/width ratio and curvature stroke features are extracted; 3) five feature vectors are computed: stroke length/ratio probability distribution function (PDF), stroke length/ratio horizontal and vertical cross-correlation, stroke length/curvature PDF, stroke length/curvature horizontal and vertical cross-correlation, and stroke length/curvature and length/ratio cross-correlation; 4) classification is carried out using different metrics and the Borda count ranking algorithm. A first experimental evaluation performed on 40 writers from the IFN/ENIT database produced a promising identification rate of 92.5% for Top1 and 100% for Top5.

On line background modeling for moving object segmentation in dynamic scenes

Fast and accurate moving object segmentation in dynamic scenes is the first step in many computer vision applications. In this paper, we propose a new background modeling method for moving object segmentation based on dynamic matrix and spatio-temporal analyses of scenes. Our method copes with some challenges related to this field. A new algorithm is proposed to detect and remove cast shadow. A comparative study by quantitative evaluations shows that the proposed approach can detect foreground robustly and accurately from videos recorded by a static camera and which include several constraints. A Highway Control and Management System called RoadGuard is proposed to show the robustness of our method. In fact, our system has the ability to control highway by detecting strange events that can happen like vehicles suddenly stopped in roads, parked vehicles in emergency zones or even illegal conduct such as going out from the road. Moreover, RoadGuard is capable of managing highways by saving information about the date and time of overloaded roads.