Predicate-based caching in mobile clients for con tinuous partial match queries

We propose XIR, a novel method for processing partial match queries on heterogeneous XML documents using information retrieval (IR) techniques. A partial match query is defined as the one having the descendent-or-self axis “//” in its path expression. In its general form, a partial match query has branch predicates forming branching paths. The objective of XIR is to efficiently support this type of queries for large-scale documents of heterogeneous schemas. XIR has its basis on the conventional schema-level methods using relational tables and significantly improves their efficiency using two techniques: an inverted index technique and a novel prefix match join. The former indexes the labels in label paths as keywords in texts, and allows for finding the label paths matching the queries more efficiently than string match used in the conventional methods. The latter supports branching path expressions, and allows for finding the result nodes more efficiently than containment joins used in the conventional methods. We compare the efficiency of XIR with those of XRel and XParent using XML documents crawled from the Internet. The results show that XIR is more efficient than both XRel and XParent by several orders of magnitude for linear path expressions, and by several factors for branching path expressions.

With the increase in the number of mobile users, the need for new type of services and applications is also on the rise. Particularly, a growing area of interest is to provide location dependent services to the mobile users. In this paper, we present a system that supports distributed processing of location-dependent continuous queries on distributed mobile data in a mobile environment using mobile agents. We investigate a scenario in which both the querying unit and the object being queried (target object) are capable of movement and the mobile unit is equipped with more powerful capabilities, including the storage of a small database and the capacity of data processing. Since our system deals with continuous queries, we propose a shared incremental update mechanism, which caches the results of the previously evaluated queries and avoids redundant results thereby minimizing the data traffic in wireless environment. To further reduce the data transfer we share the cached data among different queries. Our system uses mobile agents for evaluating queries, which involves data from both the server and mobile unit, and it helps in parallel processing of data and it, can efficiently track the mobile units involved in the system. The conventional query processing method like join processing of data from mobile units and server is directly applied in the mobile environment.

A variety of research exists for the processing of continuous queries in large, mobile environments. Each method tries, in its own way, to address the computational bottleneck of constantly processing so many queries. In this paper, we introduce an efficient and scalable system for monitoring continuous queries by leveraging the parallel processing capability of the Graphics Processing Unit. We examine a naive CPU-based solution for continuous range-monitoring queries, and we then extend this system using the GPU. Additionally, with mobile communication devices becoming commodity, location-based services will become ubiquitous. To cope with the very high intensity of location-based queries, we propose a view oriented approach of the location database, thereby reducing computation costs by exploiting computation sharing amongst queries requiring the same view. Our studies show that by exploiting the parallel processing power of the GPU, we are able to significantly scale the number of mobile objects, while maintaining an acceptable level of performance.

The main objective of this chapter is to present a general overview of existing approaches on query processing and the authors’ vision on query evaluation in pervasive environments. It illustrates, with scenarios and practical examples, existing data and streams querying systems in pervasive environments. It describes the evaluation process of (i) mobile queries and queries on moving objects, (ii) continuous queries and (iii) stream queries. Finally, the chapter introduces the authors’ vision of query processing as a service composition in pervasive environments.

In order to provide a streaming service of 3-D spatial objects to the mobile clients on a street, we propose a new query type, called continuous perspective query. The perspective query differs from conventional spatial queries in that the levels of details (LOD) of query results depend on the distance between the query point and spatial objects. The objects in the vicinity are to be provided with a higher LOD than those far from the query point. We are dealing with continuous queries, and the LODs of the results are also changing according to the distance from the mobile query point. The LOD of the result object changes from a low LOD to a high LOD as the mobile query point approaches to the object. In this paper, we also propose a processing method for continuous perspective query to reduce the processing cost at a server and communication cost between the server and the mobile clients.

An energy-efficient mobile transaction processing method using random back-off in wireless broadcast environments

Mobile clients need to access information anytime, anywhere from various legacy and existing applications on the wired network with minimum effort and cost. The challenge is to support pervasive information access to disparate data sources such as World Wide Web (WWW) and databases that can provide useful information to mobile clients without burdening the mobile device in terms of computation, storage, and power. In this paper, we propose a scheme where the nodes on the fixed network execute and manage profiles on behalf of mobile clients, we elaborate on the scheme that offers profile-based, personalized, location-aware information access in mobile environments using a distributed approach that minimizes the transmission and processing costs. Finally, we present simulation- based experimental results that characterize the efficiency and effectiveness of our approaches under various scenarios.

Chapter 7 - System Recovery

In this paper, we propose a static cache management policy for RAID architecture which uses an SSD as a disk cache. Because SSD has several drawbacks, dynamic cache management scheme such as LRU can cause serious problem i.e., too much write operations can be occurred in order to contain most recently used data. Frequent write operations on SSD not only slow down the performance but also shorten the lifetime. For this reason, we propose a static cache management policy which takes popularity and size into account. Popular data of some period is copied into SSD and too large files are excluded since too large files can lower the hit ratio. We used real trace to evaluate our scheme and the results showed that write counts are reduced to 1/37 of LRU policy as we desired. Unfortunately, the average hit ratio was lower than LRU policy but when popular data is similar between two periods, our scheme showed better hit ratio than LRU. This implies that our scheme can be used on web server which follows zipf’s distribution and has smooth changing of popular data.

Caching is a key technique for improving data retrieval performance of mobile clients. The emergence of state-of-the-art peer-to-peer communication technologies now brings to reality what we call in which mobile clients not only can retrieve data items from mobile support stations, but also from the cache in their peers, thereby inducing a new dimension for mobile data caching. In this paper, we propose a distributed group-based cooperative caching scheme, in which we define the concept of a tightly-coupled group (TCG) by capturing the data affinity of individual peers and their mobility patterns, in a mobile broadcast environment. A distributed stable peer discovery protocol is proposed for discovering all TCGs dynamically. In addition, a cache signature scheme is adopted to provide hints for the mobile clients to determine whether their required data items are cached by their neighboring peers, and to perform cooperative cache replacement to increase overall data availability. Simulation studies are conducted to evaluate the effectiveness of our distributed group-based cooperative caching scheme.

Most of the previous researches assume that each mobile client needs only one data item. However, in many situations, a mobile client might need more than one data item. In this paper, we propose an efficient scheduling method for query-set-based broadcasting, which integrates with query expansion method (QEM) and the mining association rules technique. The mining association rules can globally find the data item sets (large itemsets) which are requested by clients frequently. From our simulation results, we show that, as compared to the local optimal approach in the previous methods, our improved-QEM can construct the schedule with the smaller TQD than QEM and modified-QEM, where TQD denotes total query distance and is proportional to the average access time.

To conserve the battery capacity of mobile terminals and manage uplink bandwidth effectively, power-efficient cache management schemes that can be used in mobile environments are proposed. With the proposed schemes, the number of redundant data request messages for identical data decreases significantly compared with conventional cache management schemes.

In mobile environments, mobile clients can access information with respect to their locations by submitting Location-Dependent Spatial Queries (LDSQs) to Location- Based Service (LBS) servers. Owing to scarce wireless channel bandwidth and limited client battery life, frequent LDSQ submission from clients must be avoided. Observing that LDSQs issued from a client located at nearby positions would likely return the same query results, we explore the idea of valid scope , which represents a spatial area in which a set of LDSQs will retrieve exactly the same set of query results. With a valid scope derived and an LDSQ result cached, a client can assert whether the new LDSQs can be answered with the maintained LDSQ result, thus eliminating the need of sending LDSQs to the server. Contention on the wireless channel and client energy consumed for data transmission can be considerably reduced. In this paper, we design efficient algorithms to compute the valid scope for common types of LDSQs, including nearest neighbor queries, range queries and window queries. Through an extensive set of experiments, our proposed valid scope computation algorithms are shown to outperform existing approaches.

Mobility becomes a mode of life or work, ubiquitous access to information becomes necessary. At the same time, technological advances in wireless networks and the success of handheld computers and mobile phones are encouraging this movement. The diversity of modes of interaction in mobile environments must allow users to access information anywhere and at any time. This flexibility makes users more demanding and brings new challenges to user interfaces. For this, the context must be well understood and managed in an appropriate form to promote sharing between the different devices and offer a high level of abstraction. Several architectures have been developed to allow context management in mobile environments. To face the challenges of context management in mobile environments, and taking into account the limits of existing solutions, we offer a modular and flexible architecture, which takes the context as the most important element to reason, adapt and provide a service in a appropriate form.

Monitoring and tracking LBS applications require data-base and application support to model and manage moving objects in both database and application domains. Such services must also provide efficient processing of continuous queries over moving objects. In contrast to regular queries that are evaluated only once, a continuous query remains active over a period of time.