1888002
An Analysis and Taxonomy of Unstructured Workflows
Most workflow tools support structured workflows despite the fact that unstructured workflows can be more expressive. The reason for this is that unstructured workflows are more prone to errors. In this paper, we describe a taxonomy that serves as a framework for analyzing unstructured workflows. The taxonomy organizes unstructured workflows in terms of two considerations: improper nesting and mismatched split-join pairs. Based on this taxonomy we characterize situations that are well-behaved and others that are not. We also discuss well-behaved unstructured workflows that have equivalent structured mappings. Finally, we also introduce a relaxed notion of correctness called quasi-equivalence that is based on one-directional bisimulation. The results of our research will be useful for researchers investigating expressiveness and correctness issues in unstructured workflows.
16012186
A fine-grained, controllable, user-to-user delegation method in RBAC
This paper addresses the issues surrounding user-to-user delegation in RBAC. We show how delegations can be incorporated into the RBAC model in a simple and straightforward manner. A special feature of the model is that it allows fine-grained control over what rights a user wishes to delegate as opposed to delegation at the role level where all the rights of a role must be delegated. In addition, the model provides a rich set of controls regarding further delegations of a right, generic constraints that further control delegations, and an innovative model for revocations. Properties of both delegation and revocation are discussed, and our work is compared with other related research.
206778468
A performance study of general grid structures for replicated data
Recently, there has been considerable interest in the study of replica-control protocols which are based on organizing several copies of an object into logical structures, such as rectangular grids. In addition to high availability, another objective in exploiting such structures is to improve the degree of load sharing in a system. The authors extend the scope of grid structures to general grids, which allow holes in various positions of a rectangular structure and are useful to consider because they often produce availabilities that are higher than solid grids, where every position must be occupied by a node. In addition to proposing an improvement to the existing grid protocol, new insights are offered into the performance of the grids, from both availability and load sharing points of view. Algorithms for designing grids to maximize availability independently and also in conjunction with a load sharing constraint are given.<<ETX>>
14897390
Meta workflows as a control and coordination mechanism for exception handling in workflow systems
A higher level control and coordination mechanism is required for exception handling in workflow systems. This paper describes such a framework based on events, states, and a new kind of process called a meta workflow. Meta workflows have five kinds of meta activities and facilitate control over base workflows. We describe the framework and illustrate it with examples to show its features. The paper gives an architecture for incorporating it into existing workflows and also provides a formal semantics of execution. This framework can be used in Web services, supply chains, and inter-organizational applications where coordination requirements are complex, and flexible and adaptable workflows are needed. It is also useful for handling not just failure recovery but also various kinds of special situations, which arise frequently in web-based applications.
59757838
Operating System Support for Data Management.
7923805
A reference model for team-enabled workflow management systems
Abstract Today's workflow systems assume that each work item is executed by a single worker. From the viewpoint of the system, a worker with the proper qualifications selects a work item, executes the associated work, and reports the result. There is usually no support for teams, i.e., groups of people collaborating by jointly executing work items (e.g., the program committee of a conference, the management team of a company, a working group, and the board of directors). In this paper, we propose the addition of a team concept to today's workflow management systems. Clearly, this involves a marriage of workflow and groupware technology. To shed light on the introduction of teams, we extend the traditional organizational meta model with teams and propose a team-enabled workflow reference model. For this reference model and to express constraints with respect to the distribution of work to teams, we use object constraint language (OCL).
8829443
Exploring the trade-off between label size and stack depth in MPLS routing
Multiprotocol label switching or MPLS technology is being increasingly deployed by several of the largest Internet service providers to solve problems such as traffic engineering and to offer IP services like virtual private networks (VPNs). In MPLS, the analysis of the packet (network layer) header is performed just once, and each packet is assigned a stack of labels, which is examined by subsequent routers when making forwarding decisions. Despite the fact that MPLS is becoming widespread on the Internet, we know essentially very little about the performance one can achieve with it, and about the intrinsic trade-offs in its use of resources. In this paper, we undertake a comprehensive study of the label size versus stack depth trade-off for MPLS routing protocols on lines and trees. We show that in addition to LSP tunneling, label stacks can also be used to dramatically reduce the number of labels required for setting up MPLS LSPs in a network. Based on this observation, we develop routing algorithms and prove lower bounds for two basic problems: (1) fixed label routing: given a fixed number of labels, we want to minimize the stack depth, and (2) fixed stack routing: given a bound on the stack depth, we want to minimize the number of labels used. Our simulation results validate our approach, demonstrating that our novel protocols enable MPLS routing on large trees with few labels and small stack sizes. Thus, our MPLS routing algorithms are applicable to a number of practical scenarios involving the provisioning of VPNs and multicast trees.
28468806
Space-code bloom filter for efficient per-flow traffic measurement
Per-flow traffic measurement is critical for usage accounting, traffic engineering, and anomaly detection. Previous methodologies are either based on random sampling (e.g., Cisco's NetFlow), which is inaccurate, or only account for the "elephants". We introduce a novel technique for measuring per-flow traffic approximately, for all flows regardless of their sizes, at very high-speed (say, OC768). The core of this technique is a novel data structure called space code bloom filter (SCBF). A SCBF is an approximate representation of a multiset; each element in this multiset is a traffic flow and its multiplicity is the number of packets in the flow. The multiplicity of an element in the multiset represented by SCBF can be estimated through either of two mechanisms-maximum likelihood estimation (MLE) or mean value estimation (MVE). Through parameter tuning, SCBF allows for graceful tradeoff between measurement accuracy and computational and storage complexity. SCBF also contributes to the foundation of data streaming by introducing a new paradigm called blind streaming. We evaluate the performance of SCBF through mathematical analysis and through experiments on packet traces gathered from a tier-1 ISP backbone. Our results demonstrate that SCBF achieves reasonable measurement accuracy with very low storage and computational complexity
3276234
Minimizing average flow time on related machines
We give the first on-line poly-logarithmic competitve algorithm for minimizing average flow time with preemption on related machines, i.e., when machines can have different speeds. This also yields the first poly-logarithmic polynomial time approximation algorithm for this problem.More specifically, we give an O(log2 P • log S)-competitive algorithm, where P is the ratio of the biggest and the smallest processing time of a job, and S is the ratio of the highest and the smallest speed of a machine. Our algorithm also has the nice property that it is non-migratory. The scheduling algorithm is based on the concept of making jobs wait for a long enough time before scheduling them on slow machines.
2247483
Saturation throughput analysis of a system of interfering IEEE 802.11 WLANs
IEEE 802.11 wireless local area networks that span large buildings or campuses must comprise multiple cells, several of which must necessarily be cochannel cells. It can be shown that in such multicell networks, typically, the radio ranges of cochannel cells overlap. The paper studies the saturation throughput performance of two cochannel cells with critical overlap, i.e., their interference ranges completely overlap but no node in either cell can decode any transmissions from the other cell. We identify that the difference between the two MAC parameters, EIFS (extended interframe space) and DIFS (DCF interframe space) is a key issue and incorporate this difference as a parameter into an analytical model. The model yields a fixed point equation that yields an approximation to the saturation throughputs of the two cells. The results from the analysis are validated against ns-2 simulations. We find that with EIFS>DIFS there is substantial temporal unfairness in the channel access between the two cells, but, because of fewer collisions, the critical overlap configuration has higher per cell throughput than if the cells' decoding ranges overlapped.
1630993
Join-distinct aggregate estimation over update streams
There is growing interest in algorithms for processing andquerying continuous data streams (i.e., data that is seenonly once in a fixed order) with limited memory resources.Providing (perhaps approximate) answers to queries over suchstreams is a crucial requirement for many application environments;examples include large IP network installations where performancedata from different parts of the network needs to be continuouslycollected and analyzed.
The ability to estimate the number of distinct (sub)tuples inthe result of a join operation correlating two data streams (i.e.,the cardinality of a projection with duplicate elimination over ajoin) is an important requirement for several data-analysisscenarios. For instance, to enable real-time traffic analysis andload balancing, a network-monitoring application may need toestimate the number of distinct (<i>source</i>,destination) IP-address pairs occurring in the stream of IP packetsobserved by router <i>R</i><inf>1</inf>,where the source address is also seen in packets routed through adifferent router <i>R</i><inf>2</inf>.Earlier work has presented solutions to the individual problems ofdistinct counting and join-size estimation (without duplicateelimination) over streams. These solutions, however, arefundamentally different and extending or combining them to handleour more complex "Join-Distinct" estimation problem is far fromobvious. In this paper, we propose the <i>first</i>space-efficient algorithmic solution to the general Join-Distinctestimation problem over continuous data streams (our techniques canactually handle general <i>update streams</i>comprising tuple deletions as well as insertions). Our estimatorsare probabilistic in nature and rely on novel algorithms forbuilding and combining a new class of hash-based synopses (termed"JD <i>sketches</i>") for individual update streams. Wedemonstrate that our algorithms can provide low error,high-confidence Join-Distinct estimates using only small space andsmall processing time per update. In fact, we present lower boundsshowing that the space usage of our estimators is within smallfactors of the best possible for the Join-Distinct problem.Preliminary experimental results verify the effectiveness of ourapproach.