306 research outputs found
Checkpointing Orchestrated Web Services
Web Services are built on service-oriented architecture which is based on the notion of building applications by discovering and orchestrating services available on the web. Complex business processes can be realized by discovering and orchestrating already available services on the web. In order to make these orchestrated web services resilient to faults; we proposed a simple and elegant checkpointing policy called Call based Global Checkpointing of Orchestrated web services which specifies that when a web service calls another web service the calling web service has to save its state. But performance of the web services implementing this policy reduces due to checkpointing overhead. In an effort to improvise this policy, we propose in this paper, a checkpointing policy which uses Predicted Execution Time and Mean Time Between Failures of the called web services to make checkpointing decisions. This policy aims at reducing the required number of Call based Checkpoints but at the same time maintains the resilience of web services to faults
Semantic Web Services Provisioning
Semantic Web Services constitute an important research area, where vari ous underlying frameworks, such as WSMO and OWL-S, define Semantic Web
ontologies to describe Web services, so they can be automatically discovered,
composed, and invoked. Service discovery has been traditionally interpreted
as a functional filter in current Semantic Web Services frameworks, frequently
performed by Description Logics reasoners. However, semantic provisioning
has to be performed taking Quality-of-Service (QOS) into account, defining
user preferences that enable QOS-aware Semantic Web Service selection.
Nowadays, the research focus is actually on QOS-aware processes, so cur rent proposals are developing the field by providing QOS support to semantic
provisioning, especially in selection processes. These processes lead to opti mization problems, where the best service among a set of services has to be
selected, so Description Logics cannot be used in this context. Furthermore,
user preferences has to be semantically defined so they can be used within
selection processes.
There are several proposals that extend Semantic Web Services frameworks
allowing QOS-aware semantic provisioning. However, proposed selection
techniques are very coupled with their proposed extensions, most of them
being implemented ad hoc. Thus, there is a semantic gap between functional
descriptions (usually using WSMO or OWL-S) and user preferences, which are
specific for each proposal, using different ontologies or even non-semantic de scriptions, and depending on its corresponding ad hoc selection technique.
In this report, we give an overview of most important Semantic Web Ser vices frameworks, showing a comparison between them. Then, a thorough
analysis of state-of-the art proposals on QOS-aware semantic provisioning and
user preferences descriptions is presented, discussing about their applicabil ity, advantages, and defects. Results from this analysis motivate our research
work, which has been already materialized in two early contributions.Los servicios web semánticos constituyen un importante campo de inves tigación, en el cual distintos frameworks, como por ejemplo WSMO y OWL-S,
definen ontologías de la web semántica para describir servicios web, de for ma que estos puedan ser descubiertos, compuestos e invocados de manera
automática. El descubrimiento de servicios ha sido interpretado tradicional mente como un filtro funcional en los frameworks actuales de servicios web
semánticos, usando para ello razonadores de lógica descriptiva. Sin embargo,
las tareas de aprovisionamiento semántico deberían tener en cuenta la calidad
del servicio, definiendo para ello preferencias de usuario de manera que sea
posible realizar una selección de servicios web semánticos sensible a la cali dad.
Actualmente, el foco de la investigación está en procesos sensibles a la ca lidad, por lo que las propuestas actuales están trabajando en este campo intro duciendo el soporte adecuado a la calidad del servicio dentro del aprovisio namiento semántico, y principalmente en las tareas de selección. Estas tareas
desembocan en problemas de optimización, donde el mejor servicio de entre
un concjunto debe ser seleccionado, por lo que las lógicas descriptivas no pue den ser usadas en este contexto. Además, las preferencias de usuario deben ser
definidas semánticamente, de forma que puedan ser usadas en las tareas de
selección.
Existen bastantes propuestas que extienden los frameworks de servicios
web semánticos para habilitar el aprovisionamiento sensible a la calidad. Sin
embargo, las técnicas de selección propuestas están altamente acopladas con
dichas extensiones, donde la mayoría de ellas implementan algoritmos ad hoc.
Por tanto, existe un salto semántico entre las descripciones funcionales (nor malmente usando WSMO o OWL-S) y las preferencias de usuario, las cuales
son definidas específicamente por cada propuesta, usando ontologías distin tas o incluso descripciones no semánticas que dependen de la correspondiente
técnica de selección ad hoc
An Approach to E-marketplace Automation
E-marketplaces have become an essential part of e-commerce. In our research a decentralised agent-based e-marketplace platform was devised. The goal of our research is to improve overall supply chain service quality by allowing companies\u27 agents to evaluate the service quality of their partners through the history of their transactions. Consequently, since more informed decisions are taking place continuously and autonomously, supply chain service quality is being improved along the whole supply chain. In the article a service quality evaluation model of a supply chain is empirically evaluated
Redundant VoD Streaming Service in a Private Cloud: Availability Modeling and Sensitivity Analysis
For several years cloud computing has been generating
considerable debate and interest within IT corporations.
Since cloud computing environments provide storage and processing
systems that are adaptable, efficient, and straightforward,
thereby enabling rapid infrastructure modifications to be made
according to constantly varying workloads, organizations of
every size and type are migrating to web-based cloud supported
solutions. Due to the advantages of the pay-per-use model and
scalability factors, current video on demand (VoD) streaming
services rely heavily on cloud infrastructures to offer a
large variety of multimedia content. Recent well documented
failure events in commercial VoD services have demonstrated
the fundamental importance of maintaining high availability in
cloud computing infrastructures, and hierarchical modeling has
proved to be a useful tool for evaluating the availability of
complex systems and services. This paper presents an availability
model for a video streaming service deployed in a private
cloud environment which includes redundancy mechanisms in
the infrastructure. Differential sensitivity analysis was applied
to identify and rank the critical components of the system
with respect to service availability. The results demonstrate that
such a modeling strategy combined with differential sensitivity
analysis can be an attractive methodology for identifying which
components should be supported with redundancy in order to
consciously increase system dependability
Advanced service monitoring configurations with SLA decomposition and selection
Service Level Agreements (SLAs) for Software Services aim to clearly identify the service level commitments established between service requesters and providers. The commitments that are agreed however can be expressed in complex notations through a combination of expressions that need to evaluated and monitored efficiently. The dynamic allocation of the responsibility for monitoring SLAs (and often different parts within them) to different monitoring components is necessary as both SLAs and the components available for monitoring them may change dynamically during the operation of a service based system. In this paper we discuss an approach to supporting this dynamic configuration, and in particular, how SLAs expressed in higher-level notations can be efficiently decomposed and appropriate monitoring components dynamically allocated for each part of the agreements. The approach is illustrated with mechanical support in the form of a configuration service which can be incorporated into SLA-based service monitoring infrastructures
Business service composability on the basis of trust
In the real world a service in a business is usually composed of many component services. These component ser-vices join together to form a composite of components. The trustworthiness of component services determines the trustwor-thiness of this composite. This trustworthiness of composite ser-vice has a larger impact on the successful delivery of a service. In this paper we study that how we can determine the trustwor-thiness of this composite. Since the components in the composite form parallel or series and/or combination of parallel/series ar-rangements we use probability theory to determine the trustwor-thiness of composite service. We use a case study to demonstrate the concepts clearly
MACHS: Mitigating the Achilles Heel of the Cloud through High Availability and Performance-aware Solutions
Cloud computing is continuously growing as a business model for hosting information and communication technology applications. However, many concerns arise regarding the quality of service (QoS) offered by the cloud. One major challenge is the high availability (HA) of cloud-based applications. The key to achieving availability requirements is to develop an approach that is immune to cloud failures while minimizing the service level agreement (SLA) violations. To this end, this thesis addresses the HA of cloud-based applications from different perspectives. First, the thesis proposes a component’s HA-ware scheduler (CHASE) to manage the deployments of carrier-grade cloud applications while maximizing their HA and satisfying the QoS requirements. Second, a Stochastic Petri Net (SPN) model is proposed to capture the stochastic characteristics of cloud services and quantify the expected availability offered by an application deployment. The SPN model is then associated with an extensible policy-driven cloud scoring system that integrates other cloud challenges (i.e. green and cost concerns) with HA objectives. The proposed HA-aware solutions are extended to include a live virtual machine migration model that provides a trade-off between the migration time and the downtime while maintaining HA objective. Furthermore, the thesis proposes a generic input template for cloud simulators, GITS, to facilitate the creation of cloud scenarios while ensuring reusability, simplicity, and portability. Finally, an availability-aware CloudSim extension, ACE, is proposed. ACE extends CloudSim simulator with failure injection, computational paths, repair, failover, load balancing, and other availability-based modules
Resource-based modeling and simulation of business processes
International audienceThe simulation-based analysis of business processes (BPs) is a key activity at various phases of the BP lifecycle, from the design phase, to predict the process behavior, down to the execution and improvement phases, to recover from possible performance downgrades and/or improve the process performance. The BP analysis is usually carried out taking as input the BP description in a given BP modeling language. This paper specifically addresses BPs described in BPMN (Business Process Model & Notation) and introduces an approach that exploits both model-driven principles and the DEVS (Discrete Event System Specification) formalism to first annotate the BPMN model with the allocation of task resources described in terms of performance and reliability properties and then transform the annotated BPMN model into a DEVS-based model, which can be eventually executed to get the analysis results of interest. The BPMN annotation is carried out by use of PyBPMN, a lightweight BPMN extension that allows business analysts to specify the allocation of task resources and their properties in terms of both time-related attributes and reliability attributes. The paper overviews the proposed approach and gives the details of the DEVS components that are used to model the behavior of the corresponding BPMN primitives
A2THOS: Availability Analysis and Optimisation in SLAs
IT service availability is at the core of customer satisfaction and business success for today’s organisations. Many medium-large size organisations outsource part of their IT services to external providers, with Service Level Agreements describing the agreed availability of outsourced service components. Availability management of partially outsourced IT services is a non trivial task since classic approaches for calculating availability are not applicable, and IT managers can only rely on their expertise to fulfil it. This often leads to the adoption of non optimal solutions. In this paper we present A2THOS, a framework to calculate the availability of partially outsourced IT services in the presence of SLAs and to achieve a cost-optimal choice of availability levels for outsourced IT components while guaranteeing a target availability level for the service
RESTful Service Composition
The Service-Oriented Architecture (SOA) has become one of the most popular approaches to building large-scale network applications. The web service technologies are de facto the default implementation for SOA. Simple Object Access Protocol (SOAP) is the key and fundamental technology of web services. Service composition is a way to deliver complex services based on existing partner services. Service orchestration with the support of Web Services Business Process Execution Language (WSBPEL) is the dominant approach of web service composition. WSBPEL-based service orchestration inherited the issue of interoperability from SOAP, and it was furthermore challenged for performance, scalability, reliability and modifiability.
I present an architectural approach for service composition in this thesis to address these challenges. An architectural solution is so generic that it can be applied to a large spectrum of problems. I name the architectural style RESTful Service Composition (RSC), because many of its elements and constraints are derived from Representational State Transfer (REST). REST is an architectural style developed to describe the architectural style of the Web. The Web has demonstrated outstanding interoperability, performance, scalability, reliability and modifiability.
RSC is designed for service composition on the Internet. The RSC style is composed on specific element types, including RESTful service composition client, RESTful partner proxy, composite resource, resource client, functional computation and relaying service. A service composition is partitioned into stages; each stage is represented as a computation that has a uniform identifier and a set of uniform access methods; and the transitions between stages are driven by computational batons. RSC is supplemented by a programming model that emphasizes on-demand function, map-reduce and continuation passing. An RSC-style composition does not depend on either a central conductor service or a common choreography specification, which makes it different from service orchestration or service choreography.
Four scenarios are used to evaluate the performance, scalability, reliability and modifiability improvement of the RSC approach compared to orchestration. An RSC-style solution and an orchestration solution are compared side by side in every scenario. The first scenario evaluates the performance improvement of the X-Ray Diffraction (XRD) application in ScienceStudio; the second scenario evaluates the scalability improvement of the Process Variable (PV) snapshot application; the third scenario evaluates the reliability improvement of a notification application by simulation; and the fourth scenario evaluates the modifiability improvement of the XRD application in order to fulfil emerging requirements. The results show that the RSC approach outperforms the orchestration approach in every aspect
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