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1.
Temporal Reasoning in Workflow Systems   总被引:9,自引:0,他引:9  
In a workflow system, autonomous agents perform various activities cooperatively to complete a common task. Successful completion of the task often depends on correct synchronization and scheduling of agents' activities. It would greatly enhance the capabilities of current workflow systems if quantitative temporal constraints on the duration of activities and their synchronization requirements can be specified and reasoned about. This paper investigates such requirements and related reasoning algorithms. In particular, the paper studies the consistency, prediction and enactment services in a workflow system, and provides corresponding algorithms. The consistency service is to ensure that the specification of the temporal constraints is possible to satisfy; the prediction service is to foretell the time frame for the involved activities; and the enactment service is to schedule the activities so that, as long as each agent starts and finishes its task within the specified time period, the overall constraints will always be satisfied. For the enactment service, the paper identifies two practically interesting families of enactment schedules for autonomous agents, namely free schedules and restricted due-time schedules. In a free schedule, an agent may use any amount of time to finish the task as long as it is between the minimum and maximum time declared by the agent when the workflow is designed. A restricted due-time schedule is a more restrictive one in which the maximum amount of time that an agent may use is limited to a smaller number than the declared maximum. The paper presents efficient algorithms to find free and restricted due-time schedules. The paper also provides algorithms for the above services when multiple time granularities are involved in the temporal constraint specification.  相似文献
2.
Solving multi-granularity temporal constraint networks   总被引:4,自引:0,他引:4  
Many problems in scheduling, planning, and natural language understanding have been formulated in terms of temporal constraint satisfaction problems (TCSP). These problems have been extensively investigated in the AI literature providing effective solutions for some fragments of the general model. Independently, there has been an effort in the data and knowledge management research community for the formalization of the concept of time granularity and for its applications. This paper considers a framework for integrating the notion of time granularity into TCSP, and investigates the problems of consistency and network solution, which, in this context, involve complex manipulation of the periodic sets representing time granularities. A sound and complete algorithm for consistency checking and for deriving a solution is presented. The paper also investigates the algorithm's computational complexity and several optimization techniques specific to the multi-granularity context. An application to e-commerce workflows illustrates the benefits of the framework and the need for specific reasoning tools.  相似文献
3.
Rewriting Histories: Recovering from Malicious Transactions   总被引:2,自引:0,他引:2  
We consider recovery from malicious but committed transactions. Traditional recovery mechanisms do not address this problem, except for complete rollbacks, which undo the work of good transactions as well as malicious ones, and compensating transactions, whose utility depends on application semantics. We develop an algorithm that rewrites execution histories for the purpose of backing out malicious transactions. Good transactions that are affected, directly or indirectly, by malicious transactions complicate the process of backing out undesirable transactions. We show that the prefix of a rewritten history produced by the algorithm serializes exactly the set of unaffected good transactions. The suffix of the rewritten history includes special state information to describe affected good transactions as well as malicious transactions. We describe techniques that can extract additional good transactions from this latter part of a rewritten history. The latter processing saves more good transactions than is possible with a dependency-graph based approach to recovery.  相似文献
4.
Reasoning with advanced policy rules and its application to access control   总被引:1,自引:0,他引:1  
This paper presents a formal framework to represent and manage advanced policy rules, which incorporate the notions of provision and obligation. Provisions are those conditions that need to be satisfied or actions that must be performed by a user or an agent before a decision is rendered, while obligations are those conditions or actions that must be fulfilled by either the user or agent or by the system itself within a certain period of time after the decision. This paper proposes a specific formalism to express provisions and obligations within a policy and investigates a reasoning mechanism within this framework. A policy decision may be supported by more than one rule-based derivation, each associated with a potentially different set of provisions and obligations (called a global PO set). The reasoning mechanism can derive all the global PO sets for each specific policy decision and facilitates the selection of the best one based on numerical weights assigned to provisions and obligations as well as on semantic relationships among them. The formal results presented in the paper hold for many applications requiring the specification of policies, but this paper illustrates the use of the proposed policy framework in the security domain only.  相似文献
5.
An Algebraic Representation of Calendars   总被引:1,自引:0,他引:1  
This paper uses an algebraic approach to define temporal granularities and calendars. All the granularities in a calendar are expressed as algebraic expressions based on a single bottom granularity. The operations used in the algebra directly reflect the ways with which people construct new granularities from existing ones, and hence yield more natural and compact granularities definitions. Calendar is formalized on the basis of the algebraic operations, and properties of calendars are studied. As a step towards practical applications, the paper also presents algorithms for granule conversions between granularities in a calendar.  相似文献
6.
This paper describes data mining and data warehousing techniques that can improve the performance and usability of Intrusion Detection Systems (IDS). Current IDS do not provide support for historical data analysis and data summarization. This paper presents techniques to model network traffic and alerts using a multi-dimensional data model and star schemas. This data model was used to perform network security analysis and detect denial of service attacks. Our data model can also be used to handle heterogeneous data sources (e.g. firewall logs, system calls, net-flow data) and enable up to two orders of magnitude faster query response times for analysts as compared to the current state of the art. We have used our techniques to implement a prototype system that is being successfully used at Army Research Labs. Our system has helped the security analyst in detecting intrusions and in historical data analysis for generating reports on trend analysis. Recommended by: Ashfaq Khokhar  相似文献
7.
Policies in modern systems and applications play an essential role. We argue that decisions based on policy rules should take into account the possibility for the users to enable specific policy rules, by performing actions at the time when decisions are being rendered, and/or by promising to perform other actions in the future. Decisions should also consider preferences among different sets of actions enabling different rules. We adopt a formalism and mechanism devised for policy rule management in this context, and investigate in detail the notion of obligations, which are those actions users promise to perform in the future upon firing of a specific policy rule. We also investigate how obligations can be monitored and how the policy rules should be affected when obligations are either fulfilled or defaulted.  相似文献
8.
Numerous extended transaction models have been proposed in the literature to overcome the limitations of the traditional transaction model for advanced applications characterized by their long durations, cooperation between activities and access to multiple databases (like CAD/CAM and office automation). However, most of these extended models have been proposed with specific applications in mind and almost always fail to support applications with slightly different requirements.We propose the Multiform Transaction model to overcome this limitation. The multiform transaction model supports a variety of other extended transaction models. A multiform transaction consists of a set of component transactions together with a set of coordinators which specify the transaction completion dependencies among the component transactions. A set of transaction primitives allow the programmer to define custom completion dependencies. We show how a wide range of extended transactions can be implemented as multiform transactions, including sagas, transactional workflows, nested transactions, and contingent transactions. We allow the programmers to define their own primitives—having very well-defined interfaces—so that application specific transaction models like distributed multilevel secure transactions can also be supported.  相似文献
9.
This paper presents a general framework to define time granularity systems. We identify the main dimensions along which different systems can be characterized, and investigate the formal relationships among granularities in these systems. The paper also introduces the notion of a network of temporal constraints with (multiple) granularities emphasizing the semantic and computational differences from constraint networks with a single granularity. Consistency of networks with multiple granularities is shown to beNP‐hard in general and approximate solutions for this problem and for the minimal network problem are proposed. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献
10.
In Ref. 8, we introduced a simplifying assumption about entity-relationship diagrams (ERDs), called regularity, and showed that regular ERDs have several desirable properties. One such property is that every relation schema in the ERD's canonical relational scheme can be put into Third Normal Form. We left open there the more basic question: under what conditions would the original relation schemas actually be in Boyce-Codd Normal Form (BCNF)? Since the visible semantics of ERDs determine naturally their associated functional dependencies (fd's), it is important to know when an ERD, as designed, already has this strongest normal form given purely in terms of fd's. We show here a sufficient diagrammatic condition (loop-free) under which a regular ERD will have databases enjoying the benefits of BCNF.Partially supported by a University of Missouri Summer Research Fellowship.Work completed while on leave of absence from the Ballistic Missile Defense Advanced Technology Center, Data Processing Directorate, Huntsville, Alabama.  相似文献
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