Heinz Schweppe

Storing RDF as a graph

RDF is the first W3C standard for enriching information resources of the Web with detailed meta data. The semantics of RDF data is defined using a RDF schema. The most expressive language for querying RDF is RQL, which enables querying of semantics. In order to support RQL, a RDF storage system has to map the RDF graph model onto its storage structure. Several storage systems for RDF data have been developed, which store the RDF data as triples in a relational database. To evaluate an RQL query on those triple structures, the graph model has to be rebuilt from the triples. We present a new approach to store RDF data as a graph in a object-oriented database. Our approach avoids the costly rebuilding of the graph and efficiently queries the storage structure directly. The advantages of our approach have been shown by performance test on our prototype implementation OO-Store.

Hermes: a notification service for digital libraries

The high publication rate of scholarly material makes searching and br owsing an inconvenient way to keep oneself up-to-date. Instead of being the active part in information access, researchers want to be notified whenever a new paper in ones research area is published. While more and more publishing houses or portal sites offer notification services this approach has several disadvantages. We introduce the Hermes alerting service, a service that integrates a variety of different information providers making their heterogeneity transparent for the users. Hermes offers sophisticated filtering capabilities preventing the user from drowning in a flood of irrelevant information. From the users point of view it integrates the providers into a single source. Its simple provider interface makes it easy for publishers to join the service and thus reaching the potential readers directly. This paper presents the architecture of the Hermes service and discusses the issues of heterogeneity of information sources. Furthermore, we discuss the benefits and disadvantages of message-oriented middleware for implementing such a service for digital libraries.

Abstraction and decomposition in interoperable GIS

With the advent of distributed computing and the increasing trend towards the reuse of geographical data, a new generation of geographical information systems (GIS) is currently being specified. The key characteristics of these interoperable GIS are modularity and extensibility, and they are composed of existing software systems such as database management systems, traditional GIS, statistics packages and simulation models. (We use the terms interoperable GIS and open GIS interchangeably, however Open GIS is a trademark of the Open GIS Consortium (OGC)). They can be defined in terms of generic frameworks, which facilitates both information exchange between participating systems and the addition of new functionalities. Even though the idea of defining open GIS is not new, it is crucial that the steps necessary to design such a complex system be clearly decomposed. In this paper, we propose a layer decomposition for the design of an open GIS. Each layer corresponds to a different level of abstraction, start...

Alerting in a Digital Library Environment: Do Channels Meet the Requirements?

An Alerting Service (AS) informs its clients about new information provided by several suppliers. Special interests of clients can be defined as profiles. In the context of digital libraries, suppliers are the providers of documents. Providers are typically scientific publishers. In this paper we assume, that the providers are known to the clients. A general model and architecture of an Alerting Service is given in [1]. Channel technology has been developed for broadcast of news and continous streams of data like stock rates. For the digital library enviroment a finer granularity in profile definition than for common broadcasting is needed. In contrast to broadcast services, publishing events of multiple providers have to be presented to each client in a uniform way.

Database Systems as Middleware-Events, Notification, Messages

Database systems have been traditionally used as integration tools. Data integration was the primary goal of first generation systems. After relational technology had become a mature base for application development, new architectures where developed for the tight integration of data, procedures and all kinds of processing. This phase of DBS research and development was dominated by object-oriented database management and specific architectures like Starburst [HaCH 1990], which had a strong impact on current object-relational technology. The ubiquitous computer network has added another facet to the usage of DBS as an integration tool. In distributed environment, middleware aims at making distribution transparent. Corba or RMI are well-known examples. The call-oriented style of communication has been complemented by message-oriented, event-driven interaction of independent programs. System processes use this type of communication for decades. However, it is not well known as a mechanism on the application level - despite the fact that it has been employed for quite some time, e.g. in workflow systems [LeRo 2000]. The event-driven message passing paradigm becomes more and more important for highly distributed applications. Many kinds of interactions between applications follow a common pattern: n inde-pendent providers submit their output as messages, which in turn will be consumed asynchronously by m consumer applications. As opposed to call-level interaction, providers and consumers may or may not know each others identity. In a stock ticker application for example, there is no reason why providers should know the identity of consumers.

Using Moving Object Databases to Provide Context Information in Mobile Ad-hoc Networks

Applications deployed in mobile peer-to-peer systems have to cope with mobility and fluctuation of nodes. These dynamics restrict the reliability of communication links as well as the availability of certain nodes, services, and resources. Exploring the context of nodes can be used to anticipate these shortages. Context-awareness enables improvement of performance of systems and enables adaptation of applications in order to make their behavior more relevant with respect to their current situation. Preevaluation of context can be used to estimate future availability of crucial resources and reliability of communication links. Which information is considered to be relevant context information varies according to the application scenario. In this paper, we present a model for context information along with a mobile service that provides a local view of surrounding nodes in a Mobile Ad-hoc NETwork (MANET). The service is designed to enable efficient prediction of future stability of the vicinity of a node.

Ariadne, an Interactive Navigation and Search System for Computer Science Information on the World-Wide Web

Ariadne is a tool for interactive production and distribution of specialized information on computer science on the World-Wide Web. The key element of the Ariadne concept is the interaction between user and system. While most WWW information services can only be used passively, Ariadne enables users to decide on the contents and quality of the system and to obtain network-based, distributed scientific information on computer science.