Andrea D'Ambrogio

A model-driven method for describing and predicting the reliability of composite services

Service-oriented computing is the prominent paradigm for viewing business processes as composed of functions provided by modular and standardized services. Web services are the building blocks for the application of service-oriented computing on the Web and provide the necessary support for the consolidation of multiple services into a single composite service corresponding to the overall process. In such a context, service providers are strategically interested in both describing the quality of service (QoS) characteristics of offered services, to better qualify their offer and gain a significant advantage in the global marketplace, and predicting the level of QoS that can be offered to service consumers when building composite web services that make use of services managed by various service providers. This paper illustrates a model-driven method to automatically describe and predict the QoS of composite web services specified by use of business process execution language (BPEL). The paper specifically addresses the reliability characteristic of the QoS. The proposed method is founded on Q-WSDL, a lightweight WSDL extension for the description of the QoS characteristics of a web service, and exploits Q-WSDL to annotate reliability data onto a BPEL-based UML model of the composite service. The UML model is then used to predict and describe the reliability of the composite web service. The proposed method is illustrated by use of an example application that deals with a composite web service for the migration of PSTN telephone numbers.

A software architecture to ease the development of distributed simulation systems

The simulation of modern systems may require an amount of computational resources that might not be available on a single host. Distributed simulation (DS) provides an effective way to scale up for the increased computational requirements. However, using existing DS environments remains the main obstacle to the wide adoption of DS systems, because of their inherent complexity. This complexity can be quantitatively shown by the extra effort that the development of DS systems requires compared to the development of conventional local simulation (LS) systems. In this paper we introduce SimArch, a layered architecture that eases the development of DS systems by enabling simulation developers to effortlessly obtain a DS system or derive a DS system from the equivalent LS one. A reference model is used throughout the paper to illustrate the use of SimArch in the development of DS systems and to prove how the DS development effort is lowered down with respect to the use of a conventional DS environment.

jEQN a java-based language for the distributed simulation of queueing networks

The increasing pervasiveness of large scale networks is bringing distributed simulation (DS) to the reach of academic and business communities besides the traditional military ones. This gives academics and industry the advantage of using larger execution platforms and of reusing locally implemented simulation models as building blocks of much larger models. Developing a distributed simulator however requires learning how to use a given DS standard (such as HLA), that implies a non-negligible amount of effort. This paper addresses the problem of defining a language that can equivalently support the development of local or distributed simulators, making the use of the DS standard transparent. The HLA standard is dealt with, but the method can be extended to any other DS standard. The language (called jEQN) addresses the extended queueing network (EQN) domain, and thus it also includes primitives to facilitate the development of queueing network distributed simulators.

Simulation model building of traffic intersections

Designers of traffic systems might take advantage of the simulation-before-construction approach that allows them to study the behavior of a new or existing system by use of simulation models. Nevertheless, the use of simulation models is often hindered by the fact that the model building activity is a critical, time consuming and error prone activity if performed by use of experience and intuition only. Moreover, traffic designers do not usually have the necessary skills to effectively carry out system simulation. This paper overcomes such problems by introducing a model building method, thus enabling traffic designers to seamlessly introduce simulation-before-construction into their best practices. The method is applied to the building of simulation models of traffic intersections, with an example application to a real-world intersection.

Steps towards the automatic production of performance models of web applications

The automatic production of performance models of software products can encourage software designers to include performance validation in their best practices.The incorporation of methods for automatic production can also be of interest of CASE tool vendors to improve the capabilities of their commercial software development environments.This paper deals with a method that introduces a systematic approach towards the automatic production of performance models of web applications (i.e. software applications run on web platforms).The method takes in input two sets of data, the description of the platform architecture (a general view of the system platform and a detailed view of the packet flow in the platform itself) and a set of data that describes the workload imposed on the platform by the application.The produced model is an extended queueing network ready to be used by conventional evaluation tools to derive predictions on the performance of the software applications.An example is given of the method application, in which predictions of the performance of the application are obtained versus various combinations of the processing powers of the interacting hosts.

A SAAS-based automated framework to build and execute distributed simulations from SysML models

The development of complex systems requires the use of quantitative analysis techniques to allow a designtime evaluation of the system behavior. In this context, distributed simulation (DS) techniques can be effectively introduced to assess whether or not the system satisfies the user requirements. Unfortunately, the development of a DS requires the availability of an IT infrastructure that could not comply with time-to-market requirements and budget constraints. In this respect, this work introduces HLAcloud, a model-driven and cloud-based framework to support both the implementation of a DS system from a SysML specification of the system under study and its execution over a public cloud infrastructure. The proposed approach, which exploits the HLA (High Level Architecture) DS standard, is founded on the use of model transformation techniques to generate both the Java/HLA source code of the DS system and the scripts required to deploy and execute the HLA federation onto the PlanetLab cloud-based infrastructure.

Model-Driven Performability Analysis of Composite Web Services

Web services are the building blocks of the emerging computing paradigm based on service-oriented architectures (SOAs). A web service is a self-describing, open component that supports rapid composition of distributed applications. In a SOA context, service providers are strategically interested both to predict and describe the QoS of the offered services. This paper introduces a model-driven approach to automatically predict and describe the QoS of composite web services specified by use of the Business Process Execution Language for Web Services. The paper is founded on a lightweight QoS-oriented extension of the WSDL and specifically addresses the QoS in terms of the performability attribute, which defines a combined measure of performance and reliability. The proposed approach is illustrated by use of an example application that shows how the performability analysis may lead to predictions that do not correspond to those obtained by approaches that only consider the performance attribute.

A layered architecture for the model-driven development of distributed simulators

The development of a distributed simulator requires knowledge and skills that might be unavailable or difficult to acquire. Bringing model-driven approaches to the development of distributed simulators contributes to reduce both the need for specific skills and the development effort. To support this innovative development methodology, we introduce a layered simulation architecture named SimArch that allows to define simulation models that can be transparently transformed into simulation programs ready to be executed in a distributed (or local) mode. SimArch defines layers of services at increasing levels of abstraction on top of the execution environment, thus allowing developers to build distributed simulators without explicit knowledge about the execution environment (local/distributed) and the specific distributed simulation infrastructure (e.g., HLA). In order to show the effectiveness of the proposed approach, SimArch has been provided with an Extended Queueing Network (EQN) simulation language, which has been applied to the development of an example distributed simulator in the computer network domain.

A language for enabling model-driven analysis of business processes

The use of simulation-based approaches for the analysis of business processes enables the design-time prediction of the process behavior and/or the operation-time process reconfiguration. However, the effectiveness of BP simulation is still limited for several reasons (e.g., lack of simulation know-how of BP analysts, simulation model parameters that can be hard to gather, large semantic gap between the business process model and the simulation model). To overcome such limitations, this paper introduces a model-driven method to automatically build the executable simulation code of a business process from its abstract definition in BPMN, the standard language for specifying business processes. The simulation code is specified in eBPMN, a novel domain-specific language that has been designed and implemented according to the BPMN execution semantics.

A model-driven method for enacting the design-time QoS analysis of business processes

Business Process Management (BPM) is a holistic approach for describing, analyzing, executing, managing, and improving large enterprise business processes. A business process can be seen as a flow of tasks that are orchestrated to accomplish well-defined goals such as goods production or services delivery. From an IT perspective, BPM is closely related to a business process automation approach carried out by use of IT standards and technologies, such as service-oriented architectures (SOAs) and Web Services. This paper specifically focuses on fully automated business processes that are defined and executed as orchestrations of software services. In a BPM context, the ability to predict at design time the business process behavior assumes a strategic relevance, both to early assess whether or not the business goals are achieved and to gain a competitive advantage. A business process is typically specified by use of Business Process Modeling Notation (BPMN), the standard language for the high-level description of business processes. Unfortunately, BPMN does not support the characterization of the business process in terms of nonfunctional or QoS properties, such as performance and reliability. To overcome such a limitation, this paper introduces Performability-enabled BPMN (PyBPMN), a lightweight BPMN extension for the specification of performance and reliability properties. PyBPMN enables the design time prediction of the business processes behavior, in terms of performance and reliability properties. Such prediction activity requires the use of models that are to be first built and then evaluated. In this respect, this work introduces a model-driven method that exploits PyBPMN to predict, at design time, the performance and the reliability of a business process, either to select the process configuration that provides the best behavior or to check if a given configuration satisfies the overall requirements. The proposed model-driven method that enacts the automated analysis of a business process behavior embraces the complete business process development cycle, from the specification phase down to the implementation phase. The paper also describes how the proposed model-driven method is implemented. The several model transformations at the core of the method have been implemented by use of QVT, and the standard language for specifying model transformations provided by OMG’s MDA. The availability of such automated model transformations allows business analysts to predict the process behavior with no extra effort and without being required to own specific skills of performance or reliability theory, as shown by use of an example application.