Mikael Berndtsson

DeeDS towards a distributed and active real-time database system

DeeDS combines active database functionality with critical timing constraints and integrated system monitoring. Since the reactive database mechanisms, or rule management system, must meet critical deadlines, we must employ methods that make triggering of rules and execution of actions predictable. We will focus on the scheduling issues associated with dynamic scheduling of workloads where the triggered transactions have hard, firm or soft deadlines, and how transient overloads may be resolved by substituting transactions by computationally cheaper ones. The rationale for a loosely coupled general purpose event monitoring facility, that works in tight connection with the scheduler, is presented. For performance and predictability, the scheduler and event monitor are executing on a separate CPU from the rest of the system. Real-time database accesses in DeeDS are made predictable and efficient by employing methods such as main memory resident data, full replication, eventual consistency, and prevention of global deadlocks.

Design and implementation of an ECA rule markup language

This paper presents the design and implementation of the rule engine ruleCore and the ECA rule markup language rCML. In particular, an extensive set of event operators are shown in the rCML rule markup language.

Issues in Active Real-Time Databases

Active databases and real-time databases have gained increased interest in recent. Both active and real-time databases are considered as important technologies for supporting non-traditional applications such as computer integrated manufacturing (CIM), process control and air-traffic control. These applications are often event driven and need to react to events in a timely and efficient manner. In this paper we address the problem of merging active databases and real-time databases. Active real-time database is a fairly new area, in which very little research has been carried out so far. However, the use of active real-time database applications has a great potential. In this paper we address several issues and open questions such as semantics, assignment of time constraints and rule selection, which need to be considered when designing active real-time databases. We will highlight issues associated with event detection, rule triggering, rule selection and evaluation in a active real-time database system. A real-time event detection method for multi-level realtime systems is proposed.

Performance evaluation of object-oriented active database systems using the BEAST benchmark

This paper uses the BEAST benchmark to present the first serious performance study of object-oriented active database management systems (ADBMS). BEAST stresses the performance-critical components of active systems: event detection, event composition, rule retrieval, and rule firing. Method invocation events and transactional events are taken into account. Four systems, namely ACOOD, NAOS, Ode, and SAMOS, have been tested with the benchmark tests of BEAST. The performance measurements demonstrate achievements in the area of active database technology, but also indicate tradeoffs (e.g. between performance and functionality). Finally, the benchmark identifies optimizations and provides hints to ADBMS desigers about producing systems with adequate performance and functionality --- as well as some open issues.

Workshop report: the first international workshop on active and real-time database systems (ARTDB-95)

This report is a summary of the First International Workshop on Active and Real-Time Database Systems (ARTDB-95) [1], held at the University of Skovde in June 1995. The workshop brought together re ...

Reactive Object-Oriented Databases and CIM

This paper proposes a simple and powerful approach to associating rules with events in reactive object-oriented database systems. In it we propose a new run time subscription mechanism, which associates rules with specific event definitions. This brings optimization considerations — when to fire a rule — to the language level. The proposed subscription mechanism reduces rule checking to a minimum. It can be applied to both primitive events and composite events. Both rules and events are represented as first class objects. This architecture has been adopted in the ACOOD2 prototype on top of ONTOSTM.

Visualization of the composite event detection process

Active database rules are problematic to explain, understand, debug and design, irrespective of knowledge about active rule semantics. In order to address this problem, various types of active database tools have been proposed in the literature such as browsers, debuggers, analyzers, and explanation tools. The paper focuses on visualization of event detection for an explanation tool and it presents the first study on what to visualize with respect to event detection at the lowest level (i.e. visualization of event detection for a specific event type).

Running research-oriented final year projects for CS and IS students

In this paper we discuss the difficulties of designing and running a final year project course for computer science and information systems students. In particular, we present the design of a research-oriented final year project course, where the aim is to develop the students critical thinking and research skills. We also discuss the lessons learnt during the seven years that the course has been given.

REX, the rule and event eXplorer

Complex Event Processing (CEP) is a technology with support for matching patterns in a cloud or streams of events in order to support detection of specific combinations of event occurrences. A clever specification of event patterns may, for example, detect fraud attempts in a banking system, fire an alarm in response to hazardous situations in a control system or report suspicious customer behavior.n Several CEP engines have support for graphically modelling applications as well as perform tests and provide execution traces to verify the application behavior. We argue that it is beneficial to complement testing with formal verification in order to detect errors in early stages of development.n In this paper, we present the research prototype tool REX. REX is built as a loosely coupled front end to the timed-automata CASE tool UPPAAL. CEP applications and application specific properties can be specified in REX. To support formal verification, REX seamlessly transforms the CEP application together with the specified properties to the timed automata CASE tool UPPAAL where the properties are verified by the model-checker provided by UPPAAL.

Extending database support for coordination among agents

Coordination and collaboration are naturally used by groups for carrying out activities and solving problems that require cooperation. However, getting a set of computer agents to do the same has b ...