M. Berndtsson and J. Hansson. Issues in active real-time databases. In Proc  Home/Search   Document Details and Download   Summary   Related Articles   Check

....and timely rule execution is a major topic in Active Database Systems. The notions of events and time are tightly related. Many models allow to express real time constraints. Results from temporal logic and temporal database research are integrated into Active DBMS models. References: BB95] BH95] DBBC88] DG93] DE96] DSW95] GD93a] GD93b] GE95b] GES94] EGS92] EGS93] EGS94] FD95] Jae95] Ple95] PPS95] Ram95] SC93] SM95] SRST95] SW92] SW95a] SW95b] 3.7 Execution Model Activity management in databases is a fast developing and diverging research ....

M. Berndtsson and J. Hansson. Issues in active real-time databases. In Proc

....denotes the fact that t 1 writes d 2 . In section 5.2 we will see how this graph is used in our algorithm. Several coupling modes have been suggested between triggering and triggered transactions, e.g. immediate, deferred, detached etc. 16] It has been pointed out by several researchers (e.g. [6, 4]) that immediate and deferred coupling modes have several negative properties to be supported in real time databases. Hence in this paper, we only consider the detached coupling mode, which does not impose additional unpredictable execution time to the triggering transaction. The execution model ....

M. Berndtsson and J. Hansson. Issues in Active Real-Time Databases. In Proceedings of the International Workshop on Active and Real-Time Database Systems, June 1995.

....transactions. The first order of business is to identify a proper coupling mode. 2.1 Coupling Mode Several coupling modes have been suggested between triggering and triggered transactions, e.g. immediate, deferred, detached, etc. 14] It has been pointed out by several researchers (e.g. [7, 5]) that immediate and deferred coupling modes have several negative properties to be supported in real time databases. Hence in this paper, we only consider the detached coupling mode, which does not impose additional unpredictable execution time to the triggering transaction. The execution model ....

M. Berndtsson and J. Hansson. Issues in Active Real-Time Databases. In Proceedings of the International Workshop on Active and Real-Time Database Systems, June 1995.

....application supported by an active database system requires timely response to critical situations, the specified actions must be executed subject to some timing constraints. Various issues concerning the involvement of timing constraints in active databases are discussed in the following papers: [Berndtsson Hansson 1995], Branding Buchmann 1995] Cornelio Navathe 1993] Dayal et al. 1988] Korth et al. 1990] Prichard et al. 1994] Purimetla et al. 1993] Purimetla et al. 1994] Sivasankaran et al. 1995] 2.9 Performance Evaluation Models Several papers have been devoted to the description of ....

M. Berndtsson, J. Hansson `Issues in Active Real-Time Databases', Proceedings of the International Workshop on Active and Real-Time Database Systems, 1995.

....evaluation should be predictable. If traditional rule detection is adopted, i.e. events are detected in the same order as they occurred, then uncontrolled behavior can result with the timeliness being jeopardized as an effect due to event showers and transient overloads. Berndtsson and Hansson [BH95b] suggested a scheme for prioritized event detection and rule handling, where events are detected and rules evaluated with respect to the time of event occurrence and the 1. Active Real Time Database Systems 15 criticality of the actions that may be triggered upon that event. The event detection ....

....broadly categorized into the centralized approach, rules indexed by classes, and rules associated with specific events. With the centralized approach, all the rules have to be notified to determine which rules that are subjects for evaluation. By index the rules by classes efficiency is increased [BH95b] Neither methods can guarantee that no unnecessary rule triggering is performed. It has been suggested that rules should be associated with specific events, and then notify the rules that are specifically interest in that event [BH95b] In HiPAC it was suggested that the cost of evaluating ....

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Mikael Berndtsson and Jorgen Hansson. Issues in active realtime databases. In Berndtsson and Hansson [BH95a], pages 142--157.

....with transactions with noncritical (not hard critical) timing constraints (see Dynamic Scheduling) That is, the timing constraint of the associated transaction is used to compute the priority of the event. However, if event criticality is used without caution all event types may become critical [3]. Monitoring the environment is an issue that is investigated in the DeeDS architecture. The motivation is that the event monitor can serve as a filter, in which events can be handled systematically, and the load on the system can be reduced. However, to perform event composition on the ....

M. Berndtsson and J. Hansson. Issues in active real-time databases. In M. Berndtsson and J. Hansson, editors, Active and Real-Time Database System (ARTDB-95). Springer-Verlag, 1995.

....within an upper bound. The ECC continuously checks and computes the event input queue where incoming event instances are placed. Events are classified as critical or non critical depending on the deadline criticality and importance of the action part of the rules associated with the events [3]. The scheduling module dynamically guarantees the deadlines of the transactions. The purpose of the scheduler is to find a feasible schedule (a schedule such that the execution order of the transaction enforces the timeliness and timing requirements of the transactions are not violated) and ....

M. Berndtsson and J. Hansson. Issues in active real-time databases. In Active and Real-Time Database Systems (ARTDB-95), Proceedings of the First International Workshop on Active and Real-Time Database Systems, Skovde, Sweden, 9-11 June 1995. Springer-Verlag London Ltd., 1995.

....database constraint enforcing [27] 2.2 Technical Overview The DeeDS architecture [1] separates applicationrelated functions from critical system services. The former consist of a rule manager module, an object store (OBST [10] and a storage manager (tdbm) 7] The latter include scheduling [4], and event monitoring. The underlying distributed real time operating system kernel is OSE Delta [25] The rule manager receives event instances from the event monitor and executes rules that are triggered by the event. If the condition is satisfied the action is presented to the scheduler for ....

....its deadline. This could be in response to a transient overload detected by the scheduler. In [17] we defined a scheduling model for a deadline driven scheduler for OSE Delta. The critical system services execute on a dedicated processor to simplify overhead cost models, manage event criticality [4], avoid probe effect [28] and increase concurrency in the system. Moreover, the scheduler continuously monitors the remaining execution time of each transaction using milestones [19] We thus make use of hybrid monitoring techniques, based on both software and hardware monitoring, for predictable ....

M. Berndtsson and J. Hansson. Issues in active realtime databases. [5], pp 142--157.

....within an upper bound. The ECC continuously checks and computes the event input queue where incoming events instances are placed. Events are classified as critical or non critical depending on the deadline criticality and importance of the action part of the rules associated with the events [4], i.e. the ECC prioritizes critical events, in front of non critical events. Scheduling Module: The schedule module dynamically guarantees the deadlines of the transactions. The purpose of the scheduler is to find a feasible schedule and guarantee critical tasks in presence of non critical tasks ....

M. Berndtsson and J. Hansson. Issues in active realtime databases. In Active and Real-Time Database Systems (ARTDB-95), Proceedings of the First International Workshop on Active and Real-Time Database Systems, Skovde, Sweden, 9-11 June 1995. Springer-Verlag London Ltd., 1995.

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M. Berndtsson and J. Hansson, "Issues in Active Real-Time Databases", Proc. of the First International Workshop on Active and RealTime Database Systems (ARTDB-95), June 1995, pp.142-157.

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