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  • 1
    Electronic Resource
    Electronic Resource
    Spezifikation, Verifikation und verteilte Ausführung von Workflows in MENTOR (1997)
    Springer
    Informatik, Forschung und Entwicklung 12 (1997), S. 61-71 
    Details
    ISSN: 0949-2925
    Keywords: Schlüsselwörter: Workflow-Management ; verteilte Informationssysteme ; Spezifikationsmethoden ; Statecharts ; Key words: Workflow management ; distributed information systems ; specification methods ; state charts ; CR Subject Classification: H.4 (Information Systems Applications) ; H.4.1 (Office Automation)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Abstract. This article presents an approach to the specification, verification, and distributed execution of workflows based on state and activity charts. The formal foundation of state and activity charts is exploited at three levels. At the specification level, the formalism enforces precise descriptions of business processes while also allowing subsequent refinements. In addition, precise specifications based on other methods can be automatically converted into state and activity charts. At the level of verification, state charts are amenable to the efficient method of model checking, to verify particularly critical workflow properties. Finally, at the execution level, a state chart specification forms the basis for the automatic generation of modules that can be directly executed in a distributed manner. Within the MENTOR project, a coherent prototype system has been built that comprises all three levels: specification, verification, and distributed execution.
    Notes: Zusammenfassung. Der Artikel diskutiert die Spezifikation, Verifikation und verteilte Ausführung von Workflows mit Hilfe von State- und Activitycharts. Die formale Fundierung der State- und Activitycharts wird auf drei Ebenen ausgenutzt. Auf der Spezifikationsebene erzwingt der verwendete Formalismus präzise Beschreibungen von Geschäftsprozessen, läßt jedoch ebenfalls spätere Verfeinerungen zu. Darüber hinaus können Spezifikationen, die mit anderen Methoden erstellt wurden, weitgehend automatisch auf State- und Activitycharts abgebildet werden. Auf der Ebene der Verifikation kritischer Workflow-Eigenschaften eröffnen Statecharts die Anwendung der effizienten Methode des Modellprüfens. Auf der Ausführungsebene schließlich können aus einer Spezifikation verteilt ausführbare Komponenten generiert werden. Im Rahmen des MENTOR-Projekts wurde eine alle drei Ebenen umfassende Umgebung für die Spezifikation, Verifikation und verteilte Ausführung von Workflows realisiert.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004500050075
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  • 2
    Electronic Resource
    Electronic Resource
    Data partitioning and load balancing in parallel disk systems (1998)
    Springer
    The VLDB journal 7 (1998), S. 48-66 
    Details
    ISSN: 0949-877X
    Keywords: Key words:Parallel disk systems – Performance tuning – File striping – Data allocation – Load balancing – Disk cooling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Parallel disk systems provide opportunities for exploiting I/O parallelism in two possible ways, namely via inter-request and intra-request parallelism. In this paper, we discuss the main issues in performance tuning of such systems, namely striping and load balancing, and show their relationship to response time and throughput. We outline the main components of an intelligent, self-reliant file system that aims to optimize striping by taking into account the requirements of the applications, and performs load balancing by judicious file allocation and dynamic redistributions of the data when access patterns change. Our system uses simple but effective heuristics that incur only little overhead. We present performance experiments based on synthetic workloads and real-life traces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007780050053
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  • 3
    Electronic Resource
    Electronic Resource
    Integrated document caching and prefetching in storage hierarchies based on Markov-chain predictions (1998)
    Springer
    The VLDB journal 7 (1998), S. 141-162 
    Details
    ISSN: 0949-877X
    Keywords: Key words:Performance – Caching – Prefetching – Scheduling – Tertiary storage – Stochastic modeling – Markov chains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Large multimedia document archives may hold a major fraction of their data in tertiary storage libraries for cost reasons. This paper develops an integrated approach to the vertical data migration between the tertiary, secondary, and primary storage in that it reconciles speculative prefetching, to mask the high latency of the tertiary storage, with the replacement policy of the document caches at the secondary and primary storage level, and also considers the interaction of these policies with the tertiary and secondary storage request scheduling. The integrated migration policy is based on a continuous-time Markov chain model for predicting the expected number of accesses to a document within a specified time horizon. Prefetching is initiated only if that expectation is higher than those of the documents that need to be dropped from secondary storage to free up the necessary space. In addition, the possible resource contention at the tertiary and secondary storage is taken into account by dynamically assessing the response-time benefit of prefetching a document versus the penalty that it would incur on the response time of the pending document requests. The parameters of the continuous-time Markov chain model, the probabilities of co-accessing certain documents and the interaction times between successive accesses, are dynamically estimated and adjusted to evolving workload patterns by keeping online statistics. The integrated policy for vertical data migration has been implemented in a prototype system. The system makes profitable use of the Markov chain model also for the scheduling of volume exchanges in the tertiary storage library. Detailed simulation experiments with Web-server-like synthetic workloads indicate significant gains in terms of client response time. The experiments also show that the overhead of the statistical bookkeeping and the computations for the access predictions is affordable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007780050060
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  • 4
    Electronic Resource
    Electronic Resource
    Multi-level transaction management for complex objects: Implementation, performance, parallelism (1993)
    Springer
    The VLDB journal 2 (1993), S. 407-453 
    Details
    ISSN: 0949-877X
    Keywords: Atomicity ; complex objects ; inter- and intratransaction parallelism ; multi-level transactions ; performance ; persistence ; recovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Multi-level transactions are a varlant of open-nested transactions in which the subtransactions correspond to operations at different levels of a layered system architecture. They allow the exploitation of semantics of high-level operations to increase concurrency. As a consequence, undoing a transaction requires compensation of completed subtransactions. In addition, multi-level recovery methods must take into consideration that high-level operations are not necessarily atomic if multiple pages are updated in a single subtransaction. This article presents algorithms for multi-level transaction management that are implemented in the database kernel system (DASDBS). In particular, we show that multi-level recovery can be implemented in an efficient way. We discuss performance measurements using a synthetic benchmark for processing complex objects in a multi-user environment. We show that multi-level transaction management can be extended easily to cope with parallel subtransactions within a single transaction. Performance results are presented with varying degrees of inter- and intratransaction parallelism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01263047
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  • 5
    Electronic Resource
    Electronic Resource
    The LHAM log-structured history data access method (2000)
    Springer
    The VLDB journal 8 (2000), S. 199-221 
    Details
    ISSN: 0949-877X
    Keywords: Key words: Index structures – Storage systems – Performance – Temporal databases – Data warehouses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. Numerous applications such as stock market or medical information systems require that both historical and current data be logically integrated into a temporal database. The underlying access method must support different forms of “time-travel” queries, the migration of old record versions onto inexpensive archive media, and high insertion and update rates. This paper presents an access method for transaction-time temporal data, called the log-structured history data access method (LHAM) that meets these demands. The basic principle of LHAM is to partition the data into successive components based on the timestamps of the record versions. Components are assigned to different levels of a storage hierarchy, and incoming data is continuously migrated through the hierarchy. The paper discusses the LHAM concepts, including concurrency control and recovery, our full-fledged LHAM implementation, and experimental performance results based on this implementation. A detailed comparison with the TSB-tree, both analytically and based on experiments with real implementations, shows that LHAM is highly superior in terms of insert performance, while query performance is in almost all cases at least as good as for the TSB-tree; in many cases it is much better.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007780050004
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  • 6
    Electronic Resource
    Electronic Resource
    Load control in scalable distributed file structures (1996)
    Springer
    Distributed and parallel databases 4 (1996), S. 319-354 
    Details
    ISSN: 1573-7578
    Keywords: database ; hashing ; scalable ; distributed ; performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The paper presents a family of distributed file structures, coined DiFS, for record structured, disk resident files with key based exact or interval match access. The file is organized into buckets that are spread among multiple servers, where a server may hold several buckets. Client requests are serviced by mapping keys onto buckets and looking up the corresponding server in an address table. Dynamic growth, in terms of file size and access load, is supported by bucket splits and bucket migrations onto the existing or newly created servers. The major problem that we are addressing is achieving scalability in the sense that both the file size and the client throughput can be scaled up by linearly increasing the number of servers and dynamically redistributing the data. Unlike previous work with similar objectives, our data redistribution considers explicitly the cost/performance ratio of the system by aiming to minimize the number of servers that are used to provide the required performance. A new server is added only if the overall server load in the system does not drop below a pre-specified threshold. Simulation results demonstrate the scalability with controlled cost/performance and the importance of global load control. The impact of various tuning parameters on the effectiveness of the load control is studied in detail. Finally, we compare our approach with other approaches known to date and demonstrate that each of the previous approaches can be recast as a special case of our model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119338
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  • 7
    Electronic Resource
    Electronic Resource
    Guest Editors' Introduction (1998)
    Springer
    Distributed and parallel databases 6 (1998), S. 5-6 
    Details
    ISSN: 1573-7578
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008697329861
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  • 8
    Electronic Resource
    Electronic Resource
    Snowball: Scalable Storage on Networks of Workstations with Balanced Load (1998)
    Springer
    Distributed and parallel databases 6 (1998), S. 117-156 
    Details
    ISSN: 1573-7578
    Keywords: networks of workstations ; scalable storage ; distributed database
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Networks of workstations are an emerging architectural paradigm for high-performance parallel and distributed systems. Exploiting networks of workstations for massive data management poses exciting challenges. We consider here the problem of managing record-structured data in such an environment. For example, managing collections of HTML documents on a cluster of WWW servers is an important application for which our approach provides support. The records are accessed by a dynamically growing set of clients based on a search key (e.g., a URL). To scale up the throughput of client accesses with approximately constant response time, the records and thus also their access load are dynamically redistributed across a growing set of workstations. The paper addresses two problems of realistic workloads: skewed access frequencies to the records and evolving access patterns where previously cold records may become hot and vice versa. Our solution incorporates load tracking at different levels of granularity and automatically chooses the appropriate granularity for dynamic data migrations. Experimental results based on a detailed simulation model show that our method is indeed successful in providing scalable cost/performance and explicitly controlling its level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008609030195
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  • 9
    Electronic Resource
    Electronic Resource
    From Centralized Workflow Specification to Distributed Workflow Execution (1998)
    Springer
    Journal of intelligent information systems 10 (1998), S. 159-184 
    Details
    ISSN: 1573-7675
    Keywords: enterprise-wide workflows ; distributed execution ; synchronization ; communication costs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Current workflow management systems fall short of supporting large-scale distributed, enterprise-wide applications. We present a scalable, rigorously founded approach to enterprise-wide workflow management, based on the distributed execution of state and activity charts. By exploiting the formal semantics of state and activity charts, we develop an algorithm for transforming a centralized state and activity chart into a provably equivalent partitioned one, suitable for distributed execution. A synchronization scheme is developed that guarantees an execution equivalent to a non-distributed one. This basic solution is further refined in order to reduce communication overhead and exploit parallelism between partitions whenever possible. The developed synchronization schemes are compared in terms of the number and size of synchronization messages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008608810770
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  • 10
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    RDF-Stores und RDF-Query-Engines (2011)
    Springer
    Details
    Publication Date: 2011-02-22
    Print ISSN: 1618-2162
    Electronic ISSN: 1610-1995
    Topics: Computer Science
    Published by Springer
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