Klaus R. Dittrich

Events in an Active Object-Oriented Database System

In this paper we investigate the definition, detection, and management of events in the active object-oriented database system SAMOS. First, we present various event specification facilities based on simple but nevertheless powerful constructs which support the modelling of time aspects as well. Second we show how events can be detected in an efficient way. Finally, we deal with the internal representation of events using the benefits of the underlying data model.

Detecting composite events in active database systems using Petri nets

The detection of events in an active database system turns out to be a difficult problem due to the expressive event specification languages proposed in the recent past which include, among others, complexly defined events (composite events). Therefore, a mechanism is required that is suitable to model the semantics of composite events and to implement the event detector. We demonstrate how Petri nets can be used as the basis of such a mechanism in the context of the SAMOS active database system prototype.<<ETX>>

Three Decades of Data Intecration — all Problems Solved?

Data integration is one of the older research fields in the database area and has merged shortly after database systems were first introduced into the business world. In this paper, we briefly introduce the problem of integration and, based on an architectural perspective, give an overview of approaches to address the integration issue. We discuss the evolution from structural to semantic integration and provide a short outlook on our own research in the SIRUP (Semantic Integration Reflecting User-specific semantic Perspectives) approach.

Object-oriented database systems: the next miles of the marathon

Abstract Half a decade or so ago, object-oriented database systems have become an extremely hot topic of database research and development. At many places all over the world, people work on individual aspects or complete system prototypes. Already, some systems have even reached the marketplace. Experience shows, however, that it takes some 15 yr or more until a new software-related technology really makes it towards widespread use in large-scale applications. Obviously, then, the field of object-oriented database systems is not yet in a state where e.g. relational systems are today, and it may even be harder to get there than it has been for these latter kinds of products: there is no such thing like the object-oriented data model, a number of basic issues are still pending (better) solutions, and there is also still vast room for improved implementations. This paper first tries to bring some clarification to the notion of “object-orientation” in the context of database systems, and then elaborates on some selected features and issues where further progress seems to be especially desirable.

Argos—a configurable access control system for interoperable environments

The integration of autonomous information systems causes a fundamental problem for security management. How to ensure a consistent authorisation state if several independent software components are involved, each having an access control system of its own? In other words, how to ensure an organisation-wide security policy?

Data Integration — Problems, Approaches, and Perspectives

Data integration is one of the older research fields in the database area and has emerged shortly after database systems were first introduced into the business world. In this paper, we briefly introduce the problem of integration and, based on an architectural perspective, give an overview of approaches to address the integration issue. We discuss the evolution from structural to semantic integration and shortly present our own research in the SIRUP (Semantic Integration Reflecting User-specific semantic Perspectives) approach. Finally, an outlook to challenging areas of future research in the realm of data integration is given.

Defining the semantics of reactive components in event-driven workflow execution with event histories

The definition of exact semantics of workflows and involved processing entities is an open yet urgent problem for most systems. This paper considers the semantics and correctness of event-driven workflow execution by reactive components. The basis for the formalization in our approach is provided by an event his tory which records all the events generated during the execution of workflows by these components. Based on the formal notion of history, it is possible to determine the semantics of workflow systems as the set of event histories they can generate. It also allows to formalize the semantics of reactive components-and consequently, the semantics of workflows-as well as to check whether their observable behavior is correct. In addition to the precise understanding of event-driven workflow execution, the formalized notion of event history also serves as the specification of the workflow execution engine. Ultimately, the semantics of reactive components provides the basis for specifying transformation rules used to map these components to the execution level.

Investigating Termination in Active Database Systems with Expressive Rule Languages

The powerful functionality that active mechanisms add to database management systems presents, besides many advantages, a number of problems related to the control of their behavior. This paper deals with one of these problems: the termination of rule execution. We explain the termination aspect and the aim of termination analysis. Then, we present our approach for investigating the termination of rule execution. In contrast to others, this approach also addresses expressive rule languages as they have been proposed for various recent active database management system prototypes.

An Object-Oriented Integration Framework for Building Heterogeneous Database Systems

Abstract The construction of Heterogeneous Database Systems (HDBS) is supported by the ZOOIFI1 system by making extensive use of object-oriented concepts. We adopt the so-called framework concept from object-oriented programming to provide an integration framework that incorporates the entire design and major parts of the software necessary to establish a homogenization layer on top of autonomous local database systems in the form of cooperating, reusable classes. The amount and complexity of the specific software necessary to plug a new component system into the HDBS is reduced considerably as it just requires to override predefined abstract methods in appropriate subclasses. As the interface (global data model) of the homogenization layer, an object-oriented data model is used that in particular provides support for complex objects. Additionally, it allows to flexibly and accurately specify the global usability of data stored in a local system.

Detecting similarities in ontologies with the SOQA-SimPack toolkit

Ontologies are increasingly used to represent the intended real-world semantics of data and services in information systems. Unfortunately, different databases often do not relate to the same ontologies when describing their semantics. Consequently, it is desirable to have information about the similarity between ontology concepts for ontology alignment and integration. This paper presents the SOQA-SimPack Toolkit (SST), an ontology language independent Java API that enables generic similarity detection and visualization in ontologies. We demonstrate SST’s usefulness with the SOQA-SimPack Toolkit Browser, which allows users to graphically perform similarity calculations in ontologies.