作者：
Okano, KHigashino, TTaniguchi, KMemberFaculty of Engineering Science
Osaka University Toyonaka Japan 560 Teruo Hipshino received his B.E.
M.E.and Ph.D. degrees in Information and Computer Sciences from Osaka University Osaka Japan in 1R9 1981 and 1984 respectively. He joined the Faculty of Osaka University in 1984. Since 1991 he has been an Associate Professor in the Department of Information and Computer Sciences at Osaka University. In 1990 he was a Visiting Researcher of Dept. I.R.O. at University of Montreal Canada. His current research interests include design and analysis of distributed systems specification and verification of communication protocols and formal approach of program design. He is a member of IEEE-CS ACMIEICE of Japanand IPS of Japan.
In this paper, new methods for providing the correctness of refinement among abstract sequential machine style programs are described. The programs are described in algebraic language ASL using some useful notions, i....
详细信息
In this paper, new methods for providing the correctness of refinement among abstract sequential machine style programs are described. The programs are described in algebraic language ASL using some useful notions, i.e., the extended projection and the valid reachability condition for each transition function. These notions allow a designer to refine a given text (program or specification) to a concrete text more freely than the text that does not use such notions. These notions can also enhance the expressive power of the text. On the other hand, these advantages would have lost half their values, if useful methods to prove the correctness of refinement among the texts using them are not found. Thus new methods for proving the correctness of the texts are proposed, and they do not require much proof loads. First, the correctness of refinement among the ASL texts with the extended projection is defined. Second, a method is proposed for proving the correctness of refinement among such texts. Also proposed is a definition of the correctness of refinement among the texts with the valid reachability conditions and a method to prove their correctness. These methods do not require more proof loads than the usual methods for the texts that do not use such notions in the abstract sequential machine style. Therefore, these methods are useful.
This paper examines correctness issues that arise in distributed database design. A distributed relational database design is traditionally considered to be valid if every global relation can be reconstructed from its...
详细信息
This paper examines correctness issues that arise in distributed database design. A distributed relational database design is traditionally considered to be valid if every global relation can be reconstructed from its fragments by join operations. In this paper, three successively less restrictive definitions of validity are presented, each providing progressively improved handling of incomplete information. Examining these forms, a hybrid reconstruction approach involving inner- and outer-joins is proposed and we briefly describe its application to query formulation. We also propose replacing the notion of global reconstructability with the less restrictive, yet intuitively natural notion of object reconstructability. Universal relations need not be constructed. The need for maintenance of constraints across sites of a distributed system is discussed, and the notion of a distributed referential constraint is proposed which fulfills this need.
It is proposed that the execution of a set of join queries in a distributed environment should be considered cooperatively, rather than as a set of separate requests. With this understanding, a model of multiple query...
详细信息
It is proposed that the execution of a set of join queries in a distributed environment should be considered cooperatively, rather than as a set of separate requests. With this understanding, a model of multiple query execution in the form of a linear integer program is offered. Several requests are issued to the distributed database management system, each specifying the collation of information comprised of a number of logically distinct data sets, or relations, and dispersed across the sites of a distributed system. Performing these tasks demands the usage of limited resources, so that efficient management commands the smallest additional imposition possible. Both processors and the data communication devices that interconnect them are exploited;an optimal strategy is defined to be one that minimizes a weighted sum of the costs of computation and those of information exchange incurred in resolving the group of queries. Previous models of join query evaluation would regard each individual query in isolation, to produce a sequence of independent execution strategies, one correspondingly for every request. By instead permitting multiple utilization of intermediate computations, any overlap between these queries can be exploited to further reduce the total demand placed on the system as a whole. Through investigations into the character of a number of interacting join computations, performed at a single site in isolation, an earlier single query model [1] can be extended to facilitate the cooperative execution of an entire group.
The uncertainty inherent in the distributed environment poses new challenges to the efficient utilization of system resources in managing database transactions. In response to this realization, the execution of a join...
详细信息
The uncertainty inherent in the distributed environment poses new challenges to the efficient utilization of system resources in managing database transactions. In response to this realization, the execution of a join query in a system with probabilistic resource and cost parameters is contemplated, leading to the development of stochastic programming models. Information in the form of relational tables and scattered amongst the sites of a distributed database system is to be collated and presented to the appropriate user, in response to an issued request. Performing this task demands the usage of limited resources;the ultimate goal is the determination of an execution strategy incurring minimal cost to the system. The actual state of any network component at the moment of its exploitation cannot be exactly ascertained in advance. Any interrogation of a distant element must be communicated by the network, and this involves a delay, as perceived by the questioner, during which the state of the system may change. Indeed, the time at which a task assigned to any particular component cannot itself be precisely predicted, even if the future state of the component could be known definitively. By considering the uncertain nature of the distributed environment, the earlier model of join query evaluation presented in [1] can be modified in different ways to account for system parameters known only in a stochastic sense. This new level of subjectivity is a revelation of the many different attitudes that may be taken towards the chance of infeasibility in the solution, for the major issue in dealing with uncertainty is the choice of an appropriate measure of risk.
Traditional object-oriented real-time systems are often limited an that they provide only one approach to real-time object support. Taking the increasing demand for flexible and extensible object support environments ...
详细信息
Protocols to implement a fault-tolerant computing system are described. These protocols augment the hypervisor of a virtual-machine manager and coordinate a primary virtual machine with its backup. The result is a fau...
详细信息
For fault-tolerant computersystems (FTCS) supporting critical applications, it is of key importance to be able to answer the question of whether they indeed fulfill the quality of service requirements of their users....
详细信息
For fault-tolerant computersystems (FTCS) supporting critical applications, it is of key importance to be able to answer the question of whether they indeed fulfill the quality of service requirements of their users. In particular, answers related to the combined performance and dependability of the FTCS are important. To facilitate these so-called performability studies, we present DYQNTOOL + , a performability evaluation tool based on the dynamic queuing network concept, that allows for a combined modeling of system performance and dependability. Different from other performability evaluation tools, DYQNTOOL + combines two different modeling paradigms, i.e., queuing networks and stochastic Petri nets, for respectively the performance and the dependability aspects of the system under study. The mutual relations between these two model parts, such as workload-induced failures and performance decreases due to failures, are explicitly modeled as well. By the above choice for such a combination of modeling paradigms, the modeling can be done in greater detail, thereby often revealing system behavior that cannot be revealed otherwise. We present the dynamic queuing network modeling approach and its implementation in DYQNTOOL + , as well as illustrate its usage by addressing a number of examples.
Traditional object-oriented real-time systems are often limited an that they provide only one approach to real-time object support. Taking the increasing demand for flexible and extensible object support environments ...
详细信息
Traditional object-oriented real-time systems are often limited an that they provide only one approach to real-time object support. Taking the increasing demand for flexible and extensible object support environments into account, we discuss the design and implementation of a small object-oriented real-time executive based on a sub-framework which we call Roo. Roo is a component of the Tigger framework (our proposal for an extensible object support operating system) and is intended to support different object models providing soft real-time behaviour. Roo provides support for different mechanisms and policies for real-time thread management, scheduling and synchronization. In this it serves as a basis for other components of the Tigger framework.< >
In massively parallel SIMD machines, communication bottlenecks have been a major problem due to the limitation of available topologies. Especially they are not well suited to broadcast-type communications. Some sugges...
详细信息
In massively parallel SIMD machines, communication bottlenecks have been a major problem due to the limitation of available topologies. Especially they are not well suited to broadcast-type communications. Some suggested approaches are not practical, even though they are asymptotically fast, because they incur large minimum latency. In this paper, a simple and practical linear broadcast-type communication algorithm which is based on associative computing and does not use interconnection networks at all, is presented.< >
暂无评论