Checking Behavioral Consistency Constraints for Pervasive Context in Asynchronous Environments
Checking Behavioral Consistency Constraints for Pervasive Context in Asynchronous Environments
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发表时间：
2009-11
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通讯作者：
Yu Huang;Jianping Yu;Jiannong Cao;Xiaoxing Ma;Xianping Tao;Jian Lu
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作者：
Yu Huang;Jianping Yu;Jiannong Cao;Xiaoxing Ma;Xianping Tao;Jian Lu
上下文一致性检查，即对上下文属性的指定约束的检查，对于上下文感知应用程序至关重要。为了描述和适应普适计算环境中的动态变化，上下文感知应用程序通常需要指定和检查上下文上的行为一致性约束。这个问题之所以具有挑战性，主要是因为普适计算环境的分布式和异步特性。具体来说，检查行为约束的关键问题是上下文活动的时间顺序。上下文活动通常涉及多个上下文收集设备，这些设备是完全分散的，并以异步方式交互。然而，现有的上下文一致性检查方案不能在异步环境中工作，因为它们隐式地假设全局时钟或同步交互中继的可用性。为此，我们提出了排序全局活动（ordered Global Activity， OGA）算法，该算法在异步环境中基于谓词检测来检测全局活动的排序。我们方法的本质是消息因果关系及其作为异步环境中的逻辑矢量时钟的动态编码。我们在异步环境中实现了用于谓词检测的中间件基础设施（MIPA），在此基础上实现和评估OGA算法。评估结果显示了异步对行为一致性约束检查的影响，这证明了我们工作的主要动机。它们还表明，在动态普适计算环境中，OGA可以实现对行为一致性约束的精确检查。
Context consistency checking, the checking of specified constraint on properties of contexts, is essential to context-aware applications. In order to delineate and adapt to dynamic changes in the pervasive computing environment, context-aware applications often need to specify and check behavioral consistency constraints over the contexts. This problem is challenging mainly due to the distributed and asynchronous nature of pervasive computing environments. Specifically, the critical issue in checking behavioral constraints is the temporal ordering of contextual activities. The contextual activities usually involve multiple context collecting devices, which are fully-decentralized and interact in an asynchronous manner. However, existing context consistency checking schemes do not work in asynchronous environments, since they implicitly assume the availability of a global clock or relay on synchronized interactions. To this end, we propose the Ordering Global Activity (OGA) algorithm, which detects the ordering of the global activities based on predicate detection in asynchronous environments. The essence of our approach is the message causality and its on-the-fly coding as logic vector clocks in asynchronous environments. We implement the Middleware Infrastructure for Predicate detection in Asynchronous environments (MIPA), over which the OGA algorithm is implemented and evaluated. The evaluation results show the impact of asynchrony on the checking of behavioral consistency constraints, which justifies the primary motivation of our work. They also show that OGA can achieve accurate checking of behavioral consistency constraints in dynamic pervasive computing environments.