Fraunhofer Institut für Integrierte Publikations-und Informationssysteme IPSI

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  • Publication
    Managing and recovering high data availability in a DHT under churn
    ( 2006)
    Kneevi, P.
    ;
    Wombacher, A.
    ;
    Risse, T.
    An essential issue in peer-to-peer data management is to keep data highly available all the time. A common idea is to replicate data hoping that at least one replica is available when needed. However, due to churns, the number of created replicas could be not sufficient for guaranteeing the intended data availability. If the number of replicas is computed according to the lowest expected peer availability (a classical case), but the expectation were too high, then the peer availability after a churn could be too low, and the system could not be able to recover the requested data availability. The paper is a continuation of previous work [1] and presents an replication protocol that delivers a configured data availability guarantee, and is resistant to, or recovers fast from churns. The protocol is based on a Distributed Hash Table (DHT), measurement of peer online probability in the system, and adjustment of the number of replicas accordingly. The evaluation shows that we are able to maintain or recover the requested data availability during or shortly after stronger or weaker churns, and at the same time the storage overhead is close to the theoretical minimum.
  • Publication
    Managing and recovering high data availability in a DHT under chum
    ( 2006)
    Knezevic, P.
    ;
    Wombacher, A.
    ;
    Risse, T.
    An essential issue in peer-to-peer data management is to keep data highly available all the time. A common idea is to replicate data hoping that at least one replica is available when needed. However, due to churns, the number of created replicas could be not sufficient for guaranteeing the intended data availability. If the number of replicas is computed according to the lowest expected peer availability (a classical case), but the expectation were too high, then the peer availability after a churn could be too low, and the system could not be able to recover the requested data availability. The paper is a continuation of previous work [1] and presents an replication protocol that delivers a configured data availability guarantee, and is resistant to, or recovers fast from churns. The protocol is based on a Distributed Hash Table (DHT), measurement of peer online probability in the system, and adjustment of the number of replicas accordingly. The evaluation shows that we are able to maintain or recover the requested data availability during or shortly after stronger or weaker churns, and at the same time the storage overhead is close to the theoretical minimum.
  • Publication
    Highly available DHTs
    ( 2006)
    Knezevic, P.
    ;
    Wombacher, A.
    ;
    Risse, T.
  • Publication
    Process-annotated service discovery facilitated by an n-gram-based index
    ( 2005)
    Mahleko, B.
    ;
    Wombacher, A.
    ;
    Fankhauser, P.
  • Publication
    Requirements for secure logging of decentralized cross-organizational workflow executions
    ( 2005)
    Wombacher, A.
    ;
    Wieringa, R.
    ;
    Jonker, W.
    ;
    Kneevi, P.
    ;
    Pokraev, S.
    The control of actions performed by parties involved in a decentralized cross-organizational workflow is done by several independent workflow engines. Due to the lack of a centralized coordination control, an auditing is required which supports a reliable and secure detection of malicious actions performed by these parties. In this paper we identify several issues which have to be resolved for such a secure logging system. Further, security requirements for a decentralized data store are investigated and evaluated with regard to decentralized data stores.
  • Publication
    A grammar-based index for matching business processes
    ( 2005)
    Mahleko, B.
    ;
    Wombacher, A.
    ;
    Fankhauser, P.
  • Publication
    Intelligent web service - From web services to Plug&Play service integration
    ( 2005)
    Neuhold, E.
    ;
    Risse, T.
    ;
    Wombacher, A.
    ;
    Niederee, C.
    ;
    Mahleko, B.
    The service oriented architecture and its implementation by Web services have reached a considerable degree of maturity and also a wide adoption in different application domains. This is true for the R&D as well as for the industrial community. Standards for the description, activation, and combination of Web services have been established; UDDI registries are in place for the management of services, and development environments support the software engineer in the creation of Web services. However, the major benefit of service oriented architectures, the loose coupling of services, is still seldom explored in real world settings. The reason is the heterogeneity on different levels within the service oriented architecture. The heterogeneity problems reach from the semantics of service descriptions to compatibility problems between workflows, which have to be connected via service interfaces. In spite of compatible service signatures, workflows might, for example, not be compatible in their semantics. This talk discusses challenges and solutions for a real .Plug&Play. service infrastructure, i.e. a Web service infrastructure, where integration of new Web services becomes as simple and straightforward as plugging a USB stick into your laptop. To achieve this goal various issues have to be addressed: Semantics of services as a foundation for intelligent service mediation and usage Effective, automatic, and intelligent service discovery taking into account application context Dynamic context-aware composition of services into processes The challenges and approaches for a "Plug& Play" service infrastructure are illustrated with a real world example.
  • Publication
    Enabling high data availability in a DHT
    ( 2005)
    Kneevi, P.
    ;
    Wombacher, A.
    ;
    Risse, T.
    Many decentralized and peer-to-peer applications require some sort of data management. Besides P2P file-sharing, there are already scenarios (e.g. BRICKS project [3]) that need management of finer-grained objects including updates and, keeping them highly available in very dynamic communities of peers. In order to achieve project goals and fulfill the requirements, a decentralized/ P2P XML storage on top of a DHT (Distributed Hash Table) overlay has been proposed [6]. Unfortunately, DHTs do not provide any guarantees that data will be highly available all the time. A self-managed approach is proposed where availability is stochastically guaranteed by using a replication protocol. The protocol recreates periodically missing replicas dependent on the availability of peers. We are able to minimize generated costs for requested data availability. The protocol is fully decentralized and adapts itself on changes in community maintaining the requested availability. Finally, th e approach is evaluated and compared with replication mechanisms embedded in other decentralized storages.
  • Publication
    Matchmaking for business processes based on conjunctive finite state automata
    ( 2005)
    Wombacher, A.
    ;
    Fankhauser, P.
    ;
    Mahleko, B.
    ;
    Neuhold, E.
    Web services have a potential to enhance B2B e-commerce over the internet by allowing companies and organisations to publish their business processes on service directories where potential trading partners can find them. This can give rise to new business paradigms based on ad-hoc trading relations as companies, particularly small to medium scale, can cheaply and flexibly enter into fruitful contracts, e.g., through subcontracting from big companies. More business process support by the web service infrastructure is however needed before such a paradigm change can materialise. The current infrastructure does not provide sufficient support for searching and matching business processes. We believe that such a service is needed and will enable companies and organisations to establish ad-hoc business relations without relying on manually negotiated frame contracts like RosettaNet PIPs. This paper gives a formal semantics to business process matchmaking and an operational de scription for matchmaking. Copyright