Distributed Applications and Interoperable Systems

Frontmatter

Mobile Service Oriented Architectures (MOSOA)

Abstract

Mobile services hold a promise of utilizing the phone also for other purposes than purely communication. However, repeated attempts at realizing mobile services in the market place have been met with limited success. This article (1) defines the architectural drivers that drive success or failure of mobile services, (2) analyzes three different architectural styles of realizing such a mobile service using the example of a movie ticket selling service and (3) presents the results of this analysis. The main result of the analysis is that a serious conflict exists between usability and essentially all the other architectural drivers included in our analysis, i.e. portability, deployability and scalability. This is due to the fact that, because of the restricted state of the art technology, only native client applications offer satisfactory usability, but these do not satisfy the other drivers.

Jilles van Gurp, Anssi Karhinen, Jan Bosch

A Spatial Programming Model for Real Global Smart Space Applications

Abstract

Global smart spaces are intended to provide their inhabitants with context-aware access to pervasive services and information relevant to large geographical areas. Transportation is one obvious domain for such global smart spaces since applications can be built to exploit the variety of sensor-rich systems that have been deployed to support urban traffic control and highway management as well as within individual vehicles. This paper presents a spatial programming model designed to provide a standardised way to build context-aware global smart space applications using information that is distributed across independent (legacy, sensor-enabled, and embedded) systems by exploiting the overlapping spatial and temporal attributes of the information maintained by these systems. The spatial programming model is based on a topographical approach to modelling space that enables systems to independently define and use potentially overlapping spatial context in a consistent manner and in contrast to topological approaches, in which geographical relationships between objects are described explicitly. Moreover, this approach facilitates the incremental construction of global smart spaces since the underlying systems to be incorporated are largely decoupled. The programming model has been evaluated by building a context-aware service for multi-modal urban journey planning, as part of the development of an overall architecture for intelligent transportation systems in Dublin.

René Meier, Anthony Harrington, Thomas Termin, Vinny Cahill

Mobile Process Description and Execution

Abstract

Mobile devices are increasingly aware of their respective locations and vicinity and tend to communicate rather loosely with each other; therefore asynchronous communication paradigms are used predominately so far for corresponding mobile applications. However, while such communication mechanisms are suitable for simple activities, they may become insufficient for more complex tasks which consist of longer sequences of related activities tied together in application-oriented processes. This is of particular importance if the resulting operating sequence spans several mobile devices in frequently changing vicinities.

Therefore, the work presented here provides a concept for integrating explicit support for such mobile processes into mobile system infrastructures and for distributing their execution over different nodes in the network. For this purpose, a corresponding middleware platform (extension) for context-aware mobile applications is proposed. It supports such migrating processes and helps to execute them under the restrictions typically imposed by realistic mobile applications. In particular, this paper proposes a corresponding process description language and an execution model for mobile and distributed (business) processes in the context of the project DEMAC (Distributed Environment for Mobility-Aware Computing).

Christian P. Kunze, Sonja Zaplata, Winfried Lamersdorf

An Application Framework for Nomadic, Collaborative Applications

Abstract

To maintain availability and responsiveness, mobile applications sharing data often work on their own copy and transmit local changes to other participants. Existing systems for recording, transmitting and reconciling concurrent changes are usually ad-hoc and specific to particular applications. In contrast, we present Joyce; a general application programming framework for creating highly dynamic mobile, collaborative applications. The framework abstracts application semantics using an action-constraint formal model and provides communication and consistency services based on this model. The framework exposes an interface that allows application programmers to concentrate on core functionality without worrying about these issues. Applications made with the framework can run seamlessly across changing combination of devices, users and synchrony. We discuss the principles behind the framework, its implementation and evaluate its utility by creating a complex, shared application.

James O’Brien, Marc Shapiro

Interfering Effects of Adaptation: Implications on Self-adapting Systems Architecture

Abstract

When people are moving around using handheld networked devices, the environment for the provided services vary influencing service quality properties and user needs. In order to maintain usability and usefulness for mobile users, dynamic service adaptation is needed. Several forms of adaptation may be applied. For example, the application structure may adapt from thin client to self-reliant client, or network handover may be performed. The selection of an adaptation type is however far from obvious. Adaptation usually has impact on system resources or service quality. Also, one adaptation may require other adaptations that again have impact on resources and quality. This paper illustrates the complexity of selecting an adequate adaptation form. We argue that adaptation selection requires advanced reasoning and identify implications on the architecture of self-adapting systems.

Jacqueline Floch, Erlend Stav, Svein Hallsteinsen

Discovery of Stable Peers in a Self-organising Peer-to-Peer Gradient Topology

Abstract

Peer-to-peer (P2P) systems are characterised by a wide disparity in peer resources and capabilities. In particular, a number of measurements on deployed P2P systems show that peer stability (e.g. uptime) varies by several orders of magnitude between peers. In this paper, we introduce a peer utility metric and construct a self-organising P2P topology based on this metric that allows the efficient discovery of stable peers in the system. We propose and evaluate a search algorithm and we show that it achieves significantly better performance than random walking. Our approach can be used by certain classes of applications to improve the availability and performance of system services by placing them on the most stable peers, as well as to reduce the amount of network traffic required to discover and use these services. As a proof-of-concept, we demonstrate the design of a naming service on the gradient topology.

Jan Sacha, Jim Dowling, Raymond Cunningham, René Meier

On the Value of Random Opinions in Decentralized Recommendation

Abstract

As the amount of information available to users continues to grow, filtering wanted items from unwanted ones becomes a dominant task. To this end, various collaborative-filtering techniques have been developed in which the ratings of items by other users form the basis for recommending items that could be of interest for a specific person. These techniques are based on the assumption that having ratings from similar users improves the quality of recommendation. For decentralized systems, such as peer-to-peer networks, it is generally impossible to get ratings from all users. For this reason, research has focused on finding the best set of peers for recommending items for a specific person. In this paper, we analyze to what extent the selection of such a set influences the quality of recommendation. Our findings are based on an extensive experimental evaluation of the MovieLens data set applied to recommending movies. We find that, in general, a random selection of peers gives surprisingly good recommendations in comparison to very similar peers that must be discovered using expensive search techniques. Our study suggests that simple decentralized recommendation techniques can do sufficiently well in comparison to these expensive solutions.

Elth Ogston, Arno Bakker, Maarten van Steen

Information Agents That Learn to Understand Each Other Via Semantic Negotiation

Abstract

A key issue in Distributed Applications, that widely use Information Agents for implementing several typologies of services, is that of making reciprocally understandable the meaning of terms contained in the exchanged messages, in those cases where agents use different, heterogeneous ontologies. A possible way for facing this issue is offered by the semantic negotiation, a framework in which agents try to understand each other by negotiating the semantic of the terms. Several models and protocols of semantic negotiation have been proposed in the last years. However, most of these approaches are not able to support semantic negotiation without requiring agents either to share knowledge or to use a global common ontology, and none of them provides a semantic negotiation protocol that allows the whole agent community to contribute to the semantic understanding process between each agent pair. In this work, we propose the HIerarchical SEmantic NEgotiation (HISENE) protocol, based on the idea that an agent a should be able to partition the set of the other agents on the basis both of their personal expertise of the application domain, as well as on the particular capability that each of them shows in understanding a. We also give an implementation of the proposed protocol in the standard Java Agent DEvelopment Framework (JADE).

Salvatore Garruzzo, Domenico Rosaci

Discovering Semantic Web Services with Process Specifications

Abstract

Service discovery is one of the crucial issues for service-oriented architectural model. Recently the trend is towards semantic discovery by which semantic descriptions are the basis for service matchmaking instead of simple search based on service attributes. OWL-S is a widely adopted semantic specification for Web Services which comprises three profiles. Among those, process model is the profile that describes dynamic behaviour of Web Services in terms of functional aspects and process flows, and is generally aimed for service enactment, composition, and monitoring. This paper presents a new approach to use OWL-S process model for service discovery purpose. A Web Service can have its internal process described as an OWL-S process model specification, and a service consumer can query for a Web Service with a particular process detail. Matchmaking will be based on flexible ontological matching and evaluation of constraints on the functional behaviour and process flow of the Web Service. The architecture for process-based discovery is also presented.

Piya Suwannopas, Twittie Senivongse

Towards Building a Semantic Grid for E-Learning

Abstract

In an E-learning scenario, educational resources, such as course documents, videos, test-bases, courseware, and teacher information etc., are shared across different schools. DartGrid is built upon several techniques from both Semantic Web and Grid research areas, and is intended to offer a semantic grid toolkit for data integration. In this paper, a Semantic Grid for E-leaning based on DartGrid is introduced, and it provides a Semantic-based distributed infrastructure for E-learning resource sharing. We explore the essential and fundamental roles played by RDF semantics for e-learning, and implement a set of semantically enabled tools and grid services for E-learning such as semantic browser, ontology service, semantic query service, and semantic registration service.

Wenya Tian, Huajun Chen

A Code Migration Framework for AJAX Applications

Abstract

AJAX (Asynchronous JavaScript and XML) defines a new paradigm for writing highly interactive web applications. Prominent web sites such as Google Maps have made AJAX popular. Writing AJAX applications requires intimate knowledge of JavaScript since it is difficult to write cross-browser portable JavaScript applications. In this paper we first discuss the benefits of AJAX compared to other technologies such as Java applets. Then we propose a code migration framework that allows the programmer to write AJAX applications in Java. The Java application is automatically translated to JavaScript and migrated to the browser for execution. Our approach requires no knowledge of JavaScript. As web applications are written in Java, the developer benefits from powerful debugging tools that are not available for JavaScript. We have implemented a prototype that demonstrates the feasibility of our ideas. The prototype is available under an Open Source license.

Arno Puder

High Performance SOAP Processing Driven by Data Mapping Template

Abstract

Web Services, with loosely-coupled, high-interoperable and platform-independent characteristics, is gaining popularity in distributed computing. However, web services suffers performance penalty because its protocol stack is based on XML. SOAP is used to specify wire message format in web services, and SOAP processing largely affects the performance of web services. In this paper, we firstly analyze the performance of web services on Java platform, and identify that data model mapping between XML data and Java data is the main impact factor on performance. Therefore, we propose a new scheme of data model mapping – “Dynamic Early Binding” which enables to improve SOAP processing by avoiding Java reflection operations and proactively generating processing codes. This dynamic early binding is realized by Data Mapping Template (DMT), which is specified by extended context free grammar and implemented by pushdown automaton with output. We introduce the technique into our developed SOAP engine – SOAPExpress. The effectiveness is illustrated by yielding over 100% speedups compared to Apache Axis 1.2 in our benchmark.

Wei Jun, Hua Lei, Niu Chunlei, Zheng Haoran

An Approach for Fine-Grained Web Service Performance Monitoring

Abstract

Especially for the creation of Service-Oriented Architectures (SOA), Web service technologies are often the technology of choice. In this context, solutions for the management of Web services are becoming more and more important. This paper describes an approach to performance monitoring of Web services, which is based on the Application Response Measurement (ARM) standard. This approach enables generic (application source code-independent) and customizable instrumentation of synchronous, asynchronous and one-way Web service messages by attaching meta-data to messages.

Jan Schaefer

WSInterConnect: Dynamic Composition of Web Services Through Web Services

Abstract

In this paper, a model is presented which allows the composition of web services by means of a special web service, named WSInterConnect. Such a service might be used in a portal environment to allow interactive services lookup and creation of permanent composed services in the design stage, and for efficiently resolving missing parameters during the runtime of a process. The portal integration relies on augmented service description files based on WSGUI concepts [1], and provides a usable infrastructure for BPEL4People [4] concepts.

Josef Spillner, Iris Braun, Alexander Schill

Bounding Recovery Time in Rollback-Recovery Protocol for Mobile Systems Preserving Session Guarantees

Abstract

This paper addresses a problem of integrating the consistency management of session guarantees with recovery mechanisms in distributed mobile systems. To solve such a problem, rollback-recovery protocol rVsSG, preserving session guarantees is proposed. The protocol employs known rollback-recovery techniques, however, while applying them, the semantics of session guarantees is taken into account. Consequently, rVsSG protocol is optimized with respect to session guarantees requirements. The paper includes the proof of safety property of the presented protocol.

Jerzy Brzeziński, Anna Kobusińska, Jacek Kobusiński

Intelligent Dependability Services for Overlay Networks

Abstract

Application-level overlays have emerged as a useful means of offering network services that are not supported by the underlying physical network. Most overlays employ proprietary dependability mechanisms to render them more resilient to node failure; but the use of proprietary approaches leads to duplication of effort during development and adds design complexity. In this paper we propose generic dependability services which simplify the design of overlays. Our services are fully decentralized and are configurable to take advantage of current network conditions, which can enable us to make better repairs following failures.

Barry Porter, Geoff Coulson, Daniel Hughes

Model-Driven Development of Context-Aware Services

Abstract

In this paper, we define a model-driven design trajectory for context-aware services consisting of three levels of models with different degrees of abstraction and platform independence. The models at the highest level of platform independence describe the behaviour of a context-aware service and its environment from an integrated perspective. The models at the intermediate level describe abstract components, which realize the context-aware service in terms of a service-oriented abstract platform. At the lowest level, the realization of a context-aware service is described in terms of specific target technologies, such as Web Services, BPEL and Parlay technologies. Our approach allows service designers to concentrate their efforts on the services they intend to create and offer, by facilitating the handling of context information and auto-mating design steps through model transformation. In addition, our approach enables the reuse of platform-independent models for different target platforms.

João Paulo A. Almeida, Maria-Eugenia Iacob, Henk Jonkers, Dick Quartel

Utilising Alternative Application Configurations in Context- and QoS-Aware Mobile Middleware

Abstract

State-of-the-art dynamic middleware uses information about the environment in order to evaluate alternative configurations of an application and select one according to some criteria. In the context of applications sensitive to Quality of Service, we have identified the need for a platform independent description of configurations that includes non-functional behaviour, and that allows handling of a large number of application configurations. In this paper, we present a modelling principle and a service plan concept, which together represents such a description. The modelling principle and plan concept extend state-of-the-art with i) a model of the alternative configurations that ensure a minimum of reconfiguration steps; ii) a specification that contains information elements of the configuration, dependencies to the environment, and QoS characteristics; and iii) a platform independent specification. In the paper, we also perform a qualitative assessment of our approach, and we describe a proof-of-concept implementation.

Sten A. Lundesgaard, Ketil Lund, Frank Eliassen

Timing Driven Architectural Adaptation

Abstract

Self-adaptation is currently addressed in general frameworks and reference architectures but not in the application architecture. This paper defines concrete concepts to specify timing driven self-adaptation in the software architecture. This self-adaptation is aimed at high-end embedded component based applications. We create an architectural view of a music application describing this kind of adaptation and discuss its implementation. The novelty of our approach is the definition of separate constructs for the monitoring, the adaptation decision logic and the adaptation itself. This allows independent specification of policy and mechanisms and the possibility to adapt other applications in order to satisfy important constraints. The implementation itself consists of reusable run-time counterparts of the constructs. These counterparts are managed by the component middleware and configured by the architectural specification. This way one does not need to write additional self-adaptation code.

Andrew Wils, Yolande Berbers, Tom Holvoet, Karel De Vlaminck

Fault-Tolerant Replication Based on Fragmented Objects

Abstract

This paper describes a novel approach to fault-tolerance in distributed object-based systems. It uses the fragmented-object model to integrate replication mechanisms into distributed applications. This approach enables the use of customised code on a per-object basis to access replica groups and to manage consistency. The addition of fault tolerance to the infrastructure has only little overhead, is fully transparent for clients, and does not require internal modifications to the existing middleware. Semantic annotations at the interface level allow the developer to customise the provision of fault tolerance. Operations can be marked as read-only to allow an execution with weaker ordering semantics or as parallelisable to allow true multithreaded execution. A code-generation tool is provided to automatically produce object-specific fragment code for client access and for replica consistency management, taking into account the annotations, the interface specification, and the non-replicated implementation. A further contribution of our code-generation approach is the support of deterministic multithreading in replicated objects.

Hans P. Reiser, Rüdiger Kapitza, Jörg Domaschka, Franz J. Hauck

Towards Context-Aware Transaction Services

Abstract

For years, transactional protocols have been defined for particular application needs. Traditionally, when implementing a transaction service, a protocol is chosen and remains the same during the system execution. Nevertheless, the dynamic nature of nowadays application contexts (e.g., mobile, ad-hoc, peer-to-peer) and context variations (semantics-related aspects) motivates the need for transaction service adaptation. Next generation of transaction services should be adaptive or even better self-adaptive. This paper proposes CATE: (1) a component-based architecture of standard 2PC-based protocols and (2) a Context-Aware Transaction sErvice. Self-adaptation of CATE is obtained by context awareness and component-based reconfiguration. This allows CATE to select the most appropriate protocol with respect to the execution context. We show that using CATE performs better than using only one commit protocol in a variable system and that the reconfiguration cost is negligible.

Romain Rouvoy, Patricia Serrano-Alvarado, Philippe Merle

A Local Self-stabilizing Enumeration Algorithm

Abstract

We present a novel self-stabilizing version of Mazurkiewicz enumeration algorithm [1]. The initial version is based on local rules to enumerate nodes on an anonymous network. [2] presented the first self-stabilizing version of this algorithm which tolerates transient failures with an extension of messages complexity. Our version is based on local detection and correction of transient failures. Therefore, it ensures the fault-tolerance property without adding messages or reduces the messages’ number of other version. In addition, we have developed an interface based on the Visidia platform to simulate faults through a graphical user interface. The implementation of the presented algorithm in this platform shows its dynamic execution and validates its correction.

Brahim Hamid, Mohamed Mosbah

Adding Fault-Tolerance to a Hierarchical DRE System

Abstract

Dynamic resource management is a crucial part of the infrastructure for emerging mission-critical distributed real-time embedded system. Because of this, the resource manager must be fault-tolerant, with nearly continuous operation. This paper describes an ongoing effort to develop a fault-tolerant multi-layer dynamic resource management capability and the challenges we have encountered, including multi-tiered structure, rapid recovery, the characteristics of component middleware, and the co-existence of replicated and non-repli-cated elements. While some of these have been investigated before, this work exhibits all of these characteristics simultaneously, presenting a significant fault-tolerance research challenge.

Paul Rubel, Joseph Loyall, Richard Schantz, Matthew Gillen

Using Speculative Push for Unnecessary Checkpoint Creation Avoidance

Abstract

This paper discusses a way of incorporating speculation techniques into Distributed Shared Memory (DSM) systems with checkpointing mechanism without creating unnecessary checkpoints. Speculation is a general technique involving prediction of the future of a computation, namely accesses to shared objects unavailable on the accessing node (read faults). Thanks to such predictions objects can be pushed to requesting nodes before the actual access operation is performed, resulting, at least potentially, in a considerable performance improvement. This mechanism is a foundation for the proposed SpecCkpt protocol based on independent checkpointing integrated with a coherence protocol for a given consistency model introducing little overhead. It ensures the consistency of checkpoints, at the same time allowing a fast recovery from failures.

Arkadiusz Danilecki, Michał Szychowiak

A Versatile Kernel for Distributed AOP

Abstract

Aspect-Oriented Programming (AOP) promotes better separation of concerns in software systems by introducing aspects for the modular implementation of crosscutting concerns. As a result, modularity and adaptability of software systems are greatly enhanced. To date, very few AOP proposals take distribution into account. This paper considers the explicit introduction of distribution in AOP, by proposing support for distributed aspects: all dimensions of aspects are studied in the light of distribution. The result of this work is a versatile kernel for distributed AOP in Java: a flexible infrastructure that allows aspects to be defined and applied in a distributed manner, on top of which various distributed aspect languages and frameworks can be defined.

Éric Tanter, Rodolfo Toledo

Transformation of Centralized Software Components into Distributed Ones by Code Refactoring

Abstract

Adapting software components to be used in a particular application is a crucial issue in software component based technology. In fact, software components can be used in contexts with characteristics different from those envisaged when designing the component. Centralized or distributed deployment infrastructure can be one of these assumptions. Thus, a component can be designed as a monolithic unit to be deployed on a centralized infrastructure, nevertheless the used infrastructure needs the component to be distributed. In this paper, we propose an approach allowing to transform a centralized software component into a distributed one. Our technique is based on refactoring and fragmentation of component source code.

Abdelhak Seriai, Gautier Bastide, Mourad Oussalah

PAGE: A Distributed Infrastructure for Fostering RDF-Based Interoperability

Abstract

This paper shows how to build a scalable, robust and efficient distributed Internet-scale RDF repository, that we name PAGE (Put And Get Everywhere).

Emanuele Della Valle, Andrea Turati, Alessandro Ghioni

Erratum to: Distributed Applications and Interoperable Systems

Abstract

Erratum to: F. Eliassen and A. Montresor (Eds.) Distributed Applications and Interoperable Systems DOI: 10.​1007/​978-3-540-35127-6

The book was inadvertently published with an incorrect name of the copyright holder. The name of the copyright holder for this book is: © IFIP International Federation for Information Processing. The book has been updated with the changes.

Frank Eliassen, Alberto Montresor

Backmatter