Ahmed Hadj Kacem

Describing dynamic software architectures using an extended UML model

In this paper, we propose a new UML2.0 profile to describe the change of software architectures. The profile introduces a set of stereotypes for modeling the structural and the dynamic aspect as well as architectural constraints. We adapt the component diagrams metamodel on specific purposes by extending existing metaclasses. The adaptations are defined using stereotypes which are grouped in a profile. The profile offers to the architects an intuitive and complete way to specify the software architecture based on visual notations.

Workflow Scheduling in Cloud Computing: A Survey

Workflow systems have become a major vehiclefor easy and efficient development of scientific applications. This type of systems can benefit from the resource provisioningtechnology offered by the cloud computing. In fact, the latteroffers on-demand virtualized resources to its users. These virtualresources can be added and released dynamically. Also, usersare charged on a pay-per-use basis. How to make appropriatedecisions when allocating resources to the tasks and dispatchingthe computing tasks to resource pool has become the main issuein cloud computing. The amount of allocated resources affects theexecution time of the applications and the cost incurred by the user. In fact, resource under-provisioning will necessarily affectthe performance. In contrast, over-provisioning can result in idleinstances and cause additional costs. Then, efficient scheduling algorithms are required for selection of best suitable resources for task execution. This paper focuses on some of the important workflow scheduling strategies. It brings out an exhaustive survey of such strategies in cloud computing and includes a detailed classification of them. Then, it presents a comparative analysis of the studied approaches. Finally, it stands out a critical challenge for further research.

Towards a unified graph-based framework for dynamic component-based architectures description in Z

This paper proposes a model oriented formal approach for the specification and the verification of dynamic component-based architectures. This approach associates the expressive power of functional and structural approaches. On the one hand, we make use of the specification language Z to formulate the constraints made on the architectural style. These constraints have to be maintained during the system evolution. On the other hand, we describe the dynamic of architecture in terms of graph-rewriting rules. The obtained rules take into account structural and functional constraints of the system under their application conditions ensuring in this way its consistency during its evolution. We express the rules entirely with the Z notation also obtaining, in this way, a unified approach which treats the static as well as the dynamic aspect. To validate our specifications, we use Z-EVES which is an advanced analysis tool supporting the Z-specification language.

Specification and design of multi-agent applications using temporal z

This paper proposes a formal approach, based on stepwise refinements, for specifying and designing multi-agent applications. This approach provides a specification language which integrates temporal logic in the Z notation allowing, in this way, to cover static, behavioural, as well as dynamic aspects of multi-agent systems. Moreover, it proposes a methodology giving a set of hints and principles which help and guide the design process. Indeed, this methodology enables the user to develop step by step, in an incremental way, an implementation starting from an abstract requirements (goal) specification. Finally, we illustrate our approach by developing an agent based solution for the pursuit problem.

Formalization of Cooperation in MAS: Towards a Generic Conceptual Model

This paper proposes a formal definition of a conceptual model for cooperation among multi-agent systems (MAS). This works constitutes a part of a general research project aiming at defining a generic interaction model that covers the different facets of the cooperative activity among MAS. We propose a framework for the specification, design and verification of interaction mechanisms. Doing so, and using the Z notation, we bring closer the concepts describing a cooperative activity while integrating them with the concepts related to the organizational modelling within a MAS. Moreover, we suggest a set of necessary properties needed to maintain the consistency at the individual level (Agent) as well as at the collective level (System). The syntax and the semantic of proposed specifications have been validated with the Z-eves verification tool [1].

BPMN4CPS: A BPMN Extension for Modeling Cyber-Physical Systems

Modeling is one of the most important topics in the domain of Cyber-Physical Systems (CPS). In the field of process modelling, Business Process Modeling and Notation (BPMN) is the most used standard. However, BPMN remains limited to cater for the specific characteristics and properties of CPS such as real world properties. In this paper, we propose BPMN4CPS, which provides a set of extensions for BPMN to properly and accurately model CPS processes. In order to illustrate the applicability of BPMN4CPS, we present a case study of an ambulance drone system.

Prediction of damage in the hole-flanging process using a physically based approach

The aim of this work is to identify the limits of the hole-flanging process experimentally and numerically by a physically based approach of damage for two different aluminium alloy sheets. Two hole-flanging conditions were considered, namely hole-flanging without ironing in which the flange is formed by edge stretching, and hole-flanging with ironing in which the metal is squeezed between the punch and the die. The forming defects were characterized experimentally by scanning electron microscope observations performed in critical zones of the flanged parts. The forming defects were also predicted numerically by a 3D finite element model based on Gurson-Tvergaard-Needleman constitutive equations. To evaluate the accuracy of the developed finite element model, material damage distribution within the workpiece during the process was studied and compared with experimental observations. Furthermore, the effects of the clearance-thickness ratio on the damage behaviour were investigated for different diameter of the initial hole. This study provides relevant and new results in the design of many parts obtained by hole-flanging. Results showed that the model predicts accurately all types of failures (orange peel aspect, necking, microvoids, tear) for different conditions and both materials. Moreover, despite the large deformation induced by ironing, such conditions decrease the damage, due to void closure effects, that is in agreement with experimental results.

An UML-based approach for validation of software architecture descriptions

UML became a standard for modeling distributed architectures. The development process produces models representing architecture according to different views and different abstraction levels. These models must be valid and coherent together, so the architecture description and its evolutions have to be logical and interpretable. This paper, proposes to define intra and inter profile validations rules enabling one to define the basic elements of each profile, to minimize the modeling errors and to ensure the architecture conformity to its meta-model.

A refinement-based approach for building valid SOA design patterns

Although design patterns have become increasingly popular, most of them are presented in an informal way, which can give rise to ambiguity and may lead to their incorrect usage. Patterns proposed by the SOA design pattern community are described with informal visual notations. Modelling SOA design patterns with a standard formal notation contributes to avoid misunderstanding by software architects and helps endowing design methods with refinement approaches for mastering system architectures complexity. In this paper, we present a formal refinement-based approach that aims, first, to model message-oriented SOA design patterns with the SoaML standard language, and second to formally specify these patterns at a high level of abstraction using the Event-B method. These two steps are performed before undertaking the effective coding of a design pattern providing correct by construction pattern-based software architectures. Our approach is experimented through an example we present in this paper. We implemented our approach under the Rodin platform, which we use to prove model consistency.

Elastic Multi-tenant Business Process Based Service Pattern in Cloud Computing

Elasticity is an essential property of cloud computing. It helps service providers to efficiently exploit cloud resources and reduce servicing costs. Therefore, the multitenant business processes are long-running and they are concurrently accessed by dynamic requests from tenants. However, ensuring business process elasticity at the infrastructure and the platform levels may only result in significant resources waste due to the partner services autonomy and variability. For this purpose, we tackle the problem of handling elasticity at the process and services levels to scale-out and scale-in their service instances whenever possible. To do this, we propose an auto-scaling approach to hold the promise of ensuring the elasticity of the multitenant business process. This research is based on service patterns for integrating multi-tenancy architecture and making ecisions on the execution of the elasticity mechanisms. Furthermore, we encapsulate our approach into a middleware layer (Middleware as a Service) between the application layer and the platform layer in the cloud architecture. Provided experimental evaluations show that our approach is efficient for ensuring elasticity under various workloads variation of the business process in cloud computing.