首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 670 毫秒
1.
This paper introduces time stream Pétri nets (Ts treamPn), a model for the formal specification of multimedia synchronization scenarios. This new model extends time Pétri nets to formally describe the timed behaviour of multimedia objects and streams in asynchronous distributed systems. The proposed approach uses time intervals to label the arcs exiting from the places of the net, and typed transitions to define different firing rules. This model allows a complete and accurate specification of synchronization constraints between multimedia streams and can be used at different levels of granularity.  相似文献   

2.
3.
Hypermedia data modeling, coding, and semiotics   总被引:1,自引:0,他引:1  
This paper reviews the key issues in hypermedia systems as an overture to the proposal of a new semiotic paradigm for hypermedia data and coding models. The hypertext concept permits users to interact with and manage data as high-level conceptual objects rather than as symbol streams. Current hypermedia systems can best be defined as an amalgamation of hypertext and multimedia. While the hypertext data model enables this goal, that is not true for the data models of other media forms. A new semiotic paradigm that addresses these deficiencies and supports object-oriented interaction with compressed multimedia streams is proposed. This paper initially presents an overview of the hypertext data model, contrasting it with existing multimedia data and coding models. The framework for the new paradigm is then presented in a brief review of cognitive, psychological, and semiotic principles. This analysis culminates in the proposal of semiotically based data models and representations predisposed to the hypermedia paradigm  相似文献   

4.
A formal methodology is needed to integrate and exchange spatial and temporal properties in hypermedia and hypertext. We propose a generic framework to structure and dynamically present a new form of video- and text-based media called hypervideo. We developed a Hypervideo Engine and produced an experimental hypermedia work, HyperCafe, to illustrate the general properties and aesthetic techniques possible in such a medium  相似文献   

5.
Hall  W. 《Multimedia, IEEE》1994,1(1):60-68
In his keynote address to the Hypertext 91 conference, Frank Halasz described “ending the tyranny of the link” as a major issue facing the hypermedia research community at that time. The greatest problem is not that users always focus on buttons because they know a button indicates a link or connection of some kind. Just the opposite, users expect buttons in hypermedia systems, so if no buttons are indicated, they assume there are no links. The new, open hypermedia systems readily permit the dynamic generation of links and the application of links to standard desktop computing packages not under the hypermedia system's control. In such scenarios, buttons rapidly become less and less necessary, or useful, as a means of indicating a link. Indeed, since a button's main purpose in a hypermedia system is to indicate the presence of links, buttons should become redundant as we move toward systems where links themselves are virtual entities. Unfortunately, this is unlikely to happen whilst hypermedia authors and users have such a fixation on buttons. The author explores why the button so dominates today's hypermedia systems and why this must change  相似文献   

6.
Our research addresses evaluating the usability of hypermedia systems oth offline (CD-ROMs) and online (Web) - and tries to capture the features that most characterize the specific nature of these systems. In this article, we describe an inspection technique that lets evaluators concentrate on the usability of specific aspects of hypermedia applications, such as information and navigation structuring, media integration and synchronization, and so on, without neglecting the surface aspects. Our technique uses operational guidelines, called abstract tasks (ATs), which systematically drive the inspection activities, allowing even less experienced evaluators to come up with valuable results. As they currently exist, we see ATs as evaluation patterns, which make it possible to maximize the reuse of an evaluator's expertise. That is, reuse takes advantage of previous work, thus reducing the effort to create a new one. ATs support the reuse of an evaluator's know-how. Their goal is to capture usability inspection expertise and to express it in a precise and understandable form, so that others can easily reproduce, communicate and exploit it. Our current work is devoted to extending the AT library to cover specific usability issues related to e-commerce Web sites  相似文献   

7.
Time plays a crucial role in access control for new computing environments, which is not supported in traditional access control models. In this paper, we propose a Generalized Temporal History Based Access Control (GTHBAC) model, aimed at integrating history-based constraints along with a generic access control model. GTHBAC enhances the specification of user-defined authorization rules by constraining time interval and temporal expression over users’ history of accesses. Due to different application needs, GTHBAC uses two different time schemes, i.e., real time and logical time, in its authorization rules. A formal semantics for temporal authorizations is provided, and conflicting situations are also investigated and resolved in the model. To represent the applicability of the proposed model, an architecture for an access control system based on the model is proposed, and a case of employing the model in specifying and enforcing access control policies in a banking system is studied. The operators of GTHBAC are also compared with Linear Time Temporal Logic (LTL) operators to show the expressive power of the model.  相似文献   

8.
计算机支持多用户协同编著系统模型   总被引:9,自引:0,他引:9  
文中提出了协同编著系统的基本要求,描述了时间、空间上分散而在任务上又相互依赖的多个作者的交互方式、协作机制,分析了协同编著要素,提出了协同编著系统的逻辑模型,研究了协同编著系统中多用户文档的、操作和并发控制模型,分析了同步会议的管理模型、会议的同步模型和消息的管理策略;最生设计了相应的系统结构模型。  相似文献   

9.
Goose  S. Hall  W. Reich  S. 《Multimedia, IEEE》2000,7(3):52-60
Increased amounts of information and users' rising demands for advanced link services pose strong challenges to distributed hypermedia systems. Novel presentation facilities, nontextual digital media, personalization of content and structures, and many more techniques often require complex processing and thus imply new interaction styles. Microcosm TNG (The Next Generation), which is a framework for distributed open hypermedia, offers new mechanisms for desktop and Internet integration. It also promotes a modular approach to authoring hypermedia resources  相似文献   

10.
本文研究两个LS超混沌系统的自适应函数映射同步问题。根据李雅普诺夫稳定性原理,结合自适应函数映射同步控制方法和参数自适应规律,设计出响应系统的控制规律和参数自适应规律,实现响应系统参数未知时的自适应函数映射同步,并对参数进行正确辨识。数值仿真结果表明了方案的有效性。  相似文献   

11.
This paper presents our work on modeling and performance analysis of inventory systems using batch deterministic and stochastic Petri nets (BDSPNs). It addresses issues frequently raised by industrial companies, but did not receive enough attention by the Petri nets (PNs) community in spite of its important role in the study of discrete event systems. The BDSPN is a new class of PNs capable of describing the synchronization of discrete and batch token flows in discrete batch processes. Such processes appear in inventory systems or more general supply chains where materials are purchased in finite discrete quantities (batches of different sizes), and many operations such as inventory replenishment and customer order fulfillment are usually performed in a batch way because of the batch nature of customer orders and/or in order to take advantages of the economies of scale. In this paper, the BDSPN model is formally introduced, and its conflict resolutions of transitions and batch firing indexes are addressed. The model is then applied to the modeling and performance evaluation of various inventory systems. Analytic performance evaluation techniques are developed for the model with illustrative applications to the inventory systems. Our study shows that the model is powerful for both modeling and performance evaluation of the systems.  相似文献   

12.
Hypermedia information systems, because of their inherent qualities of nonlinearity and associative linking, offer the potential of facilitating enhanced knowledge representation and construction for users. These capabilities will be more fully realized if hypermedia information systems are developed and implemented based on constructivist learning theory. This paper examines the qualities of hypermedia systems that enable them to facilitate learning, discusses the background of current learning theories, and provides a brief view of a possible hypermedia system based on constructivist learning principles that could be developed through the use of intelligent autonomous agents.  相似文献   

13.
14.
Timed communicating sequential processes (TCSP) language is used to specify fine-grain and coarse-grain multimedia synchronization. A lip synchronization system is an example of fine-grain synchronization. Several groupware scenarios are examples of coarse-grain synchronization. The formal specifications are used as the basis of verification and simulation. Safety and liveness timing requirements of the synchronization system are stated in terms of temporal logic formulas. Correctness analysis of the specification is shown using the temporal formulas and TCSP proof theory. It is shown that TCSP is powerful enough to be used in multimedia system design and verification. Next, simulation of multimedia synchronization is discussed. Various simulation models are developed for fine- and coarse-grain synchronization systems. It is shown that simulation modeling can lead to early detection of possible synchronization violations. The buffering requirements of a given synchronization mechanism can be effectively studied using simulation  相似文献   

15.
A simple combination of nonlinear and linear digital signal processing methods is proposed for efficient noise reduction in zero crossing detectors. The method is very robust against strong impulsive noise, typically encountered in thyristor power converters, where reliable zero crossing detection is required for firing synchronization. A systematic design procedure is described for the proposed filter-based synchronization method, taking into account the specified line frequency tolerance. The fully digital signal processing approach allows compact implementations, and supports flexible interfacing to digital motor control systems  相似文献   

16.
本文首先介绍了采用对象合成Petri网(OCPN)实现多媒体同步的方法,分析了OCPN的局限性,给出了支持交互操作的多媒体时间同步模型I—OCPN,并给出了实现交互操作的具体算法。  相似文献   

17.
With the advent of fast microprocessors, refinements in the control systems for thyristor-fed DC drives have become possible. In such drives, the problem of detecting the true zero crossings of the input voltage, when the main supply is contaminated with noise spikes, is quite important. A new approach for this problem, based on the predictive synchronization concept, is presented. The algorithm also covers other aspects, like generation of firing pulses and closed-loop calculations for the drive control. The microcomputer-based system has been tested on a separately excited DC motor, and the test results are presented  相似文献   

18.
毛北行 《电子学报》2000,48(11):2215-2219
研究分数阶多混沌系统滑模同步两种方法的比较.分别设计了分数阶滑模面和非奇异终端滑模面,并证明了其稳定性.基于自适应方法设计了控制器和适应规则,得到分数阶多混沌系统取得滑模同步的两个充分条件.并用数值仿真对结论进行了验证.  相似文献   

19.
20.
This paper presents a microprocessor-based scheme that generates the necessary synchronization logical signals for three-phase static power converter control systems. The problem of detecting the phase-to-phase voltage zero-crossing in presence of noise generated by thyristor commutations in constant and in variable frequency supplies is discussed, and a microcomputer software solution is proposed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号