2,820 research outputs found
Static Analysis of Deterministic Negotiations
Negotiation diagrams are a model of concurrent computation akin to workflow
Petri nets. Deterministic negotiation diagrams, equivalent to the much studied
and used free-choice workflow Petri nets, are surprisingly amenable to
verification. Soundness (a property close to deadlock-freedom) can be decided
in PTIME. Further, other fundamental questions like computing summaries or the
expected cost, can also be solved in PTIME for sound deterministic negotiation
diagrams, while they are PSPACE-complete in the general case.
In this paper we generalize and explain these results. We extend the
classical "meet-over-all-paths" (MOP) formulation of static analysis problems
to our concurrent setting, and introduce Mazurkiewicz-invariant analysis
problems, which encompass the questions above and new ones. We show that any
Mazurkiewicz-invariant analysis problem can be solved in PTIME for sound
deterministic negotiations whenever it is in PTIME for sequential
flow-graphs---even though the flow-graph of a deterministic negotiation diagram
can be exponentially larger than the diagram itself. This gives a common
explanation to the low-complexity of all the analysis questions studied so far.
Finally, we show that classical gen/kill analyses are also an instance of our
framework, and obtain a PTIME algorithm for detecting anti-patterns in
free-choice workflow Petri nets.
Our result is based on a novel decomposition theorem, of independent
interest, showing that sound deterministic negotiation diagrams can be
hierarchically decomposed into (possibly overlapping) smaller sound diagrams.Comment: To appear in the Proceedings of LICS 2017, IEEE Computer Societ
Search and Result Presentation in Scientific Workflow Repositories
We study the problem of searching a repository of complex hierarchical
workflows whose component modules, both composite and atomic, have been
annotated with keywords. Since keyword search does not use the graph structure
of a workflow, we develop a model of workflows using context-free bag grammars.
We then give efficient polynomial-time algorithms that, given a workflow and a
keyword query, determine whether some execution of the workflow matches the
query. Based on these algorithms we develop a search and ranking solution that
efficiently retrieves the top-k grammars from a repository. Finally, we propose
a novel result presentation method for grammars matching a keyword query, based
on representative parse-trees. The effectiveness of our approach is validated
through an extensive experimental evaluation
Workflow-Net Based Cooperative Multi-Agent Systems
Workflow-nets are mathematical frameworks that are used to formally describe, model and implement workflows. First, we propose critical section workflow nets (abbreviated WFCSnet). This framework allows feedbacks in workflow systems while ensuring the soundness of the workflow. Feedback is generally not recommended in workflow systems as they threaten the soundness of the system. The proposed WFCSnet allows safe feedback and limits the maximum number of activities per workflow as required. A theorem for soundness of WFCSnet is presented. Serializability, Separability, Quasi-liveness and CS-Properties of WFCSnet are examined and some theorems and lemmas are proposed to mathematically formalize them. In this thesis, we define some formal constructs that we then build upon. We define the smallest formal sub-workflow that we call a unit. We propose some mathematical characteristics for the unit and show how it can be used. We study similarities between units and whether two units can be used interchangeably or not. We then use composites out of simple units to build more complex constructs and we study their properties. We define the concept of cooperation and propose a mathematical definition of the concept. We discuss the concept of task coverage and how it affects cooperation. We claim that task coverage is necessary for any task to be achieved and therefore, a necessity for cooperation. We use mathematical methods to determine the task coverage and the candidate cooperative partners based on their capabilities that can contribute to the desired task. Workflow-net based cooperative behaviour among agents is proposed. First, we propose a cooperative algebra, which takes the desired objective of cooperation as a plan and then transforms this plan into a workflow-net structure describing dependencies and concurrency among sub-workflow elements constituting the overall plan. Our proposed cooperative algebra converts the plan into a set of matrices that model the cooperative workflow among agents. We then propose a cooperative framework with operators that assign tasks to agents based on their capabilities to achieve the required task
LSTM Networks for Data-Aware Remaining Time Prediction of Business Process Instances
Predicting the completion time of business process instances would be a very
helpful aid when managing processes under service level agreement constraints.
The ability to know in advance the trend of running process instances would
allow business managers to react in time, in order to prevent delays or
undesirable situations. However, making such accurate forecasts is not easy:
many factors may influence the required time to complete a process instance. In
this paper, we propose an approach based on deep Recurrent Neural Networks
(specifically LSTMs) that is able to exploit arbitrary information associated
to single events, in order to produce an as-accurate-as-possible prediction of
the completion time of running instances. Experiments on real-world datasets
confirm the quality of our proposal.Comment: Article accepted for publication in 2017 IEEE Symposium on Deep
Learning (IEEE DL'17) @ SSC
Quantitative analysis of distributed systems
PhD ThesisComputing Science addresses the security of real-life systems by using
various security-oriented technologies (e.g., access control solutions
and resource allocation strategies). These security technologies
signficantly increase the operational costs of the organizations in
which systems are deployed, due to the highly dynamic, mobile and
resource-constrained environments. As a result, the problem of designing
user-friendly, secure and high efficiency information systems
in such complex environment has become a major challenge for the
developers.
In this thesis, firstly, new formal models are proposed to analyse the
secure information
flow in cloud computing systems. Then, the opacity of work
flows in cloud computing systems is investigated, a threat
model is built for cloud computing systems, and the information leakage
in such system is analysed. This study can help cloud service
providers and cloud subscribers to analyse the risks they take with
the security of their assets and to make security related decision.
Secondly, a procedure is established to quantitatively evaluate the
costs and benefits of implementing information security technologies.
In this study, a formal system model for data resources in a dynamic
environment is proposed, which focuses on the location of different
classes of data resources as well as the users. Using such a model, the
concurrent and probabilistic behaviour of the system can be analysed.
Furthermore, efficient solutions are provided for the implementation of
information security system based on queueing theory and stochastic
Petri nets. This part of research can help information security officers
to make well judged information security investment decisions
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