Data caching and perfecting strategies for location dependent information access in mobile environments

Abstract

In recent years, generations of wireless network technology, mobilephones and the internet have revolutionized the mobile communicationenvironment and lifestyle of the people across the world. With thesetechnologies and the ubiquity of location finding capabilities have spurred thedevelopment of a plethora of new mobile information services known aslocation based services, where people can acquire and disseminateinformation at any place, any time. Location based services are characterizedby providing users with useful location dependent local information such asenhanced emergency services, yellow pages, entertainment and businessservices as the pervasive data access through mobile devices are availablewherever they are. A location dependent information system uses businessand landmark information, that has been compiled into Points of Interest orPlaces of Interest databases.A location dependent information system uses location dependentquery to provide the user with information such as the nearest hospital,nearest fuel station to a current location in an unknown place. The nearestneighbor and range queries are very popular location dependent queries. Anearest neighbor query retrieves the point of interest object of a certain classwhich is closest to a certain object or location and range query retrieves theobjects located within a certain range or region.The location dependent information system, being wireless in 2nature, and dependent on pervasive access of location related information isplagued by mobility constraints like limited bandwidth, computational power,resource limitations, power constraints of smart mobile devices, clientmobility and intermittent connectivity. An ideal location dependentinformation system should provide fast access to a high diversity of points ofinterest objects for a large number of mobile users via wireless channels.The client-side data caching is considered as one of the significanttechniques in a mobile environment because it improves access latency anddata availability in case of disconnection. Caching frequently used data itemsin the mobile clients’ local storage will save client’s energy and alleviate thenetwork bandwidth contention imposed on wireless mobile systems. As sucha desirable caching technique should allow clients to assert query which canbe completely answered by locally cached data. Caching reduces networkbandwidth usage and load on the server. As a result it improves the systemthroughput, reduces user-perceived delays and improves data accessperformance. It also improves data availability in circumstances where theclients are weakly connected or totally disconnected, as well as reducesenergy consumption, since wireless communication is not required for cachehits.The major goal of this research work is to develop new models toaddress issues pertaining to client side data caching and prefetching strategies 3in order to achieve an efficient and effective location dependent informationaccess in mobile environments.The issues of cache replacement for location dependent data undera geometric location model is studied and a new cache replacement policy isproposed. This model considers the points of interest service type, area ofvalid scope, angle of bearing, beeline distance and access frequency whileanswering the nearest neighbor query to get the most relevant closest points ofinterest object to the user inan emergency scenario irrespective of the movingdirection.An efficient weighted association rule mining based dataprefetching scheme is proposed to identify points of interest object to beprefetched while answering the location dependent query by integrating theopening time of objects.A semantic caching mechanism is proposed to answer nearestneighbor and range queries from the semantic description in the cache byproposing the concept of partial objects in order to accurately answer userqueries. The model is designed to store nearest neighbor and range queryresults as semantic regions in the cache using re-entry probability, area ofvalid scope, age, rate of access as the spatial and temporal parameters in acache replacement policy.A new cachereplacement weighted network distance based policyis proposed by considering spatial factors such as network distance, weights 4on the road network and weighted density of the valid scope and temporalfactors such as opening time of the points of interestobjects and accessfrequency, calculated replacement score for eviction.An ontology-based user profile preference framework is proposedby collecting user profile and preferences for discovering the most relevantpoints of interest services with respect to user preferences.Extensive empirical studies are conducted to evaluate theperformance of proposed approaches for cache management, prefetching,semantic caching, nearest neighbor query access in the road network and onthe ontology based user preference model. The experimental resultsdemonstrate the efficiency of the proposed approaches and their superiorityover state-of-the-art approaches in the corresponding domains. The thesispresents an overview of all the proposed caching policies and models inorderto enhance the location dependent information system and suggests certainenhancements for the emerging mobile environment scenarios.