Maude Manouvrier

TQoS: Transactional and QoS-Aware Selection Algorithm for Automatic Web Service Composition

Web Services are the most famous implementation of service-oriented architectures that has brought some challenging research issues. One of these is the composition, i.e., the capability to recursively construct a composite Web service as a workflow of other existing Web services, which are developed by different organizations and offer diverse functionalities (e.g., ticket purchase, payment), transactional properties (e.g., compensatable or not), and Quality of Service (QoS) values (e.g., execution price, success rate). The selection of a Web service, for each activity of the workflow, meeting the users requirements, is still an important challenge. Indeed, the selection of one Web service among a set of them that fulfill some functionalities is a critical task, generally depending on a combined evaluation of QoS. However, the conventional QoS-aware composition approaches do not consider the transactional constraints during the composition process. This paper addresses the issue of selecting and composing Web services not only according to their functional requirements but also to their transactional properties and QoS characteristics. We propose a selection algorithm that satisfies users preferences, expressed as weights over QoS criteria and as risk levels defining semantically the transactional requirements. Proofs and experimental results are presented.

QoS-Driven Selection of Web Services for Transactional Composition

Web services composition has been gaining interest over the last years as it leverages the capabilities to offer complex operations resulting from the aggregation of Web services offered by different organizations. As composite Web services are often long-running, loosely coupled and cross-organizational applications, advanced transactional support is required to ensure reliable execution. In addition, in the presence of multiple Web services with equivalent functionality, users will discriminate the alternatives based on their quality of service (QoS). This paper address the issue of selecting and composing Web services not only according to their functional requirements but also to their transactional properties and QoS characteristics defined using a quality model. In this model, Web services are selected in a way that satisfies user preferences. These preferences are expressed as weights over QoS criterion and as risk level defining semantically the transactional requirements.

Embedding spatial information into image content description for scene retrieval

This article presents @D-TSR, an image content representation describing the spatial layout with triangular relationships of visual entities, which can be symbolic objects or low-level visual features. A semi-local implementation of @D-TSR is also proposed, making the description robust to viewpoint changes. We evaluate @D-TSR for image retrieval under the query-by-example paradigm, on contents represented with interest points in a bag-of-features model: it improves state-of-the-art techniques, in terms of retrieval quality as well as of execution time, and is scalable. Finally, its effectiveness is evaluated on a topical scenario dedicated to scene retrieval in datasets of city landmarks.

CPN-TWS: a coloured petri-net approach for transactional-QoS driven Web Service composition

In this paper, we address the issue of selecting and composing Web Services (WSs) considering functional and Quality of Service (QoS) requirements combined with transactional properties. We formalise the WS functional, QoS and transactional properties as well as the WS Composition problem. We have extended Coloured Petri Net (CPN) formalism to incorporate transactional WSs properties in the composition process. We present and prove our CPN Transactional WS (CPN-TWS) selection algorithm that satisfies the user query functional conditions expressed as input and output attributes, QoS requirements represented by weights over criteria, and transactional properties expressed as a risk level. The result of our algorithm is a CPN corresponding to a Transactional Composite WS whose WS components locally optimise the QoS. We present experimental results to study the performance and the efficiency of our selection algorithm compared with an exhaustive one.

Quadtree representations for storage and manipulation of clusters of images

This article gives an overview of different approaches proposed for the storage and manipulation of clusters of images. Clustering images consists of grouping together images having a defined relationship. In this article, images are represented by quadtrees implemented in a hierarchical or linear way. The discussion, presented at the end of the article, allows selecting a quadtree-based representation well adapted to a specific area of application or to the characteristics of the manipulated images.

Web Service Selection for Transactional Composition

In this work we address the issue of selecting and composing Web Services (WSs) considering functional requirements and transactional properties. We formalize the WS composition problem using the user query, the transactional properties of WSs and the composite WSs definition. We extends Colored Petri Net (CPN) formalism to incorporate transactional WSs properties. We present a CPN-WS selection algorithm that satisfies the user query functional conditions expressed as input and output attributes, and transactional properties expressed as a risk level. The result of our algorithm is a Colored Petri-Net allowing to execute a transactional composite WS.

Web services composition

A web service is a modular and self-described application callable with standard web technologies. A workflow describes how to combine the functionalities of different web services in order to create a new value added functionality resulting in composite web service. QoS-aware web service composition means to select a composite web service that maximizes a QoS objective function while satisfying several QoS constraints (e.g. price or duration). The workflow-based QoS-aware web service composition problem has received a lot of interest, mainly in web service community. This general problem is NP-hard since it is equivalent to the multidimensional multiple choice knapsack problem (MMKP). In this article, the theoretical complexity is analysed more precisely in regard to the property of the workflow structuring the composition. For some classes of workflows and some QoS models, the composition problem can be solved in polynomial time (since the workflow is a series-parallel directed graph). Otherwise, when there exist one or several QoS constraints to verify, the composition problem becomes NP-hard. In this case, we propose a new mixed integer linear program to represent the problem with a polynomial number of variables and constraints. Then, using CPLEX, we present some experimental results showing that our proposed model is able to solve big size instances.

Storage and Management of Similar Images

Numerical images are becoming more and more important and an increasing emphasis on multimedia applications has resulted in large volumes of images. However, images need a large memory space to be stored, so their efficient storage and retrieval generate challenges to the database community. This paper proposes a new algorithm for an efficient storage of sets of images. It is based on a version approach used in databases. It shows how to store and operate on similar images; two images are defined as similar if the quad-trees encoding them have only few different nodes. A data structure called Generic Quad-Tree (GQT) is proposed. It optimizes the memory space required to store similar images and allows an efficient navigation among them. An Image Tree stores the ancestors and descendants of an image, like a version hierarchy. Using the Image Tree, the Generic Quad-Tree allows an image to share common parts with its ancestors and descendants. The GQT approach and some algorithms for reading, modifying or removing images from the Generic Quad-Tree are described. Examples using black and white images and gray scale images are presented.

A Hierarchical Model for TransactionalWeb Service Composition in P2P Networks

The recent approaches for Web services composition tend to integrate heterogeneous business processes executed in Peer-to-Peer networks. In such networks, component Web services are invoked on independent peers and are orchestrated according to the transactional requirements defined by the designers or the users of the composite Web service. Since component Web services can be dynamically invoked and are generally implemented as black boxes, concurrency between them may appear. This paper presents the transactional execution model of composite Web services exploiting the transactional properties of their component Web services. The proposed concurrency control is ensured by a decentralized serialization graph based on an optimistic protocol and on the hierarchical structure of the composition. The globally correct execution of the composite Web service is achieved by communication among dependent subtrans-actions and the peers they have accessed.

Optimal and Automatic Transactional Web Service Composition with Dependency Graph and 0-1 Linear Programming

In this article, we propose a model based on 0-1 linear programming for automatically determining a transactional composite web service (CWS) from a service dependency graph that optimizes a QoS measure. The QoS measure used in this model can be either a classical weighted sum of QoS criteria or a minmax-type criterion (e.g. response time). The transactional properties are a set of rules that ensures a reliable execution of the resulting CWS. The proposed 0-1 linear program is solved using a standard solver (CPLEX). Our experiments show that this new exact model surpasses two main related approaches: an approximate one based on transactional requirements and an exact one, based on 0-1 linear programming (LP), but not dealing with transactional properties. In a large majority of the test sets used for our experiments, our model finds a better solution more rapidly than both related approaches and is able to guarantee its optimality. Moreover, our model is able to find the optimal solutions of big size test sets, as the ones proposed by the Web Service Challenge 2009.