Optimal Reduction of Two-Terminal Directed Acyclic Graphs

Bein, Wolfgang; Kamburowski, Jerzy; Stallmann, Matthias F.

doi:10.1137/0221065

Cited by 101 publications

(71 citation statements)

References 33 publications

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“…The number of reduction nodes is actually a commonly used metric to measure how far from an SP structure a structure may be [17]. In that sense, merging such nodes would make the rewritten workflow being further from an SP structure compared to the original workflow structure.…”

Section: Discussionmentioning

confidence: 99%

Distilling structure in Taverna scientific workflows: a refactoring approach

et al. 2014

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BackgroundScientific workflows management systems are increasingly used to specify and manage bioinformatics experiments. Their programming model appeals to bioinformaticians, who can use them to easily specify complex data processing pipelines. Such a model is underpinned by a graph structure, where nodes represent bioinformatics tasks and links represent the dataflow. The complexity of such graph structures is increasing over time, with possible impacts on scientific workflows reuse. In this work, we propose effective methods for workflow design, with a focus on the Taverna model. We argue that one of the contributing factors for the difficulties in reuse is the presence of "anti-patterns", a term broadly used in program design, to indicate the use of idiomatic forms that lead to over-complicated design. The main contribution of this work is a method for automatically detecting such anti-patterns, and replacing them with different patterns which result in a reduction in the workflow's overall structural complexity. Rewriting workflows in this way will be beneficial both in terms of user experience (easier design and maintenance), and in terms of operational efficiency (easier to manage, and sometimes to exploit the latent parallelism amongst the tasks).ResultsWe have conducted a thorough study of the workflows structures available in Taverna, with the aim of finding out workflow fragments whose structure could be made simpler without altering the workflow semantics. We provide four contributions. Firstly, we identify a set of anti-patterns that contribute to the structural workflow complexity. Secondly, we design a series of refactoring transformations to replace each anti-pattern by a new semantically-equivalent pattern with less redundancy and simplified structure. Thirdly, we introduce a distilling algorithm that takes in a workflow and produces a distilled semantically-equivalent workflow. Lastly, we provide an implementation of our refactoring approach that we evaluate on both the public Taverna workflows and on a private collection of workflows from the BioVel project.ConclusionWe have designed and implemented an approach to improving workflow structure by way of rewriting preserving workflow semantics. Future work includes considering our refactoring approach during the phase of workflow design and proposing guidelines for designing distilled workflows.

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Section: Discussionmentioning

confidence: 99%

Distilling structure in Taverna scientific workflows: a refactoring approach

et al. 2014

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“…Similarly, two parameters define the network structure: complexity index (CI) and the coefficient of network complexity (CNC). CI is a measure developed by Bein et al (1992) to assess how far the given network is from being series-parallel. It is defined to be the minimum number of node reductions required to reduce a given two terminal directed acyclic graph into a single-arc graph, when used together with series and parallel reductions.…”

Section: Computational Resultsmentioning

confidence: 99%

Robust scheduling and robustness measures for the discrete time/cost trade-off problem

Hazır

Haouari

Erel

2010

European Journal of Operational Research

116

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a b s t r a c tProjects are often subject to various sources of uncertainties that have a negative impact on activity durations and costs. Therefore, it is crucial to develop effective approaches to generate robust project schedules that are less vulnerable to disruptions caused by uncontrollable factors. In this paper, we investigate the robust discrete time/cost trade-off problem, which is a multi-mode project scheduling problem with important practical relevance. We introduce surrogate measures that aim at providing an accurate estimate of the schedule robustness. The pertinence of each proposed measure is assessed through computational experiments. Using the insights revealed by the computational study, we propose a two-stage robust scheduling algorithm. Finally, we provide evidence that the proposed approach can be extended to solve a complex robust problem with tardiness penalties and earliness revenues.

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“…In our deadline and budget problems, such a node reduction implies a decomposition of the problem into m(i) separate problems, where m(i) is the number of time-cost alternatives of the activity i corresponding to arc u → v. In each decomposed problem, we obtain the time-cost tradeoff functions for arcs u → w 1 , u → w 2 , ..., u → w k by adding the time duration and activity cost of u → v to the time-cost tradeoff functions of v → w 1 , v → w 2 , ..., v → w k , respectively. Bein et al [2] have developed an efficient method for determining the minimum number of node reductions in order to reduce the given project network to a single activity. They refer to this minimum number of node reductions as reduction complexity.…”

Section: Discussionmentioning

confidence: 99%

“…Any two-terminal directed acyclic network can be reduced to a single arc via series, parallel, and node reductions (see [2]). A node reduction operation can be applied when the node concerned has either in-degree 1 or out-degree 1.…”

Section: Discussionmentioning

confidence: 99%