| In mobile computing environment, the problems of narrow communication bandwidth, frequent network disconnections and limited mobile terminal resources lead to the bottlenecks in data accessing, which greatly challenges the mobile clients in taking query processing in mobile computing environment. Data caching in the client-side to reduce access to the database server is the key to resolve this problem. One of the traditional cache technologies, the page cache, adopting the static time and space attribute, is sensitive to the physical structure of the database and it will cause a great deal of network communication consumption and space redundancy in the situation of bad spatial agglomeration rate of data in database. The other traditional cache technology, the tuple caching, however, has the defects of expensive overhead communication, parallel processing difficulties, and can not support data processing when the network is disconnect and low efficiency in consistency maintenance and so on. Therefore, it is clearly inappropriate to adopt the traditional caching technology in the unstable network connections, limited network resources and expensive network communication mobile computing environment. So, a new cache technology is urgently needed to support mobile client access data in the case of network disconnecting or weak connecting.Semantic caching is a client cache based on the semantics related to the customer queries. its content is composed of the results of the previous query and the corresponding semantic descriptions. As the data access of mobile clients present good semantics correlation in most cases and adopt the semantic cache, the client can use the local cache of the previous query and inferring semantic information to determine whether the answers of the customer queries contains in the local cache or not and use local caching data to answer the customer's query as much as possible. The query processing strategy established on the semantic caching can reduce access to the database, reduce network data traffic, improve the query response time and reduce the network overhead. Thus semantic cache can satisfy the query processing requirements in mobile computing environment. At present, many experts and scholars have carried out the relative studies on semantic cache, the contents of which cover the semantic cache model, semantic caching query processing, semantic cache replacement, semantic cache consistency maintenance, semantic cache query cutting optimization and so on.To the current hot issues of semantic caching, this article made studies mainly in the aspects of semantic caching query processing and semantic caching query cutting optimization.In the aspect of query processing research, the paper directed that the query could be derived from the formal definition, discusses in detail the various relations between matching query and cache and their criterion conditions, detection query and the remaining queries, based on which the paper proposes the semantic caching query processing strategies on the basis of single table. The main tasks are as the follow: 1) For the original amending query processing involving abstract concepts and difficult to realize, an Improved Amending Query Processing Strategy was proposed. when the query cache is included but can not be exported from the cache, the additional amendments to cache queries will add the missing property, making inquiries to export from the cache to increase the cache hit rate and utilization; 2) It gave out the Invalid Query Processing to solve the problems that users, sometimes, submit an invalid query (such as an invalid attribute, invalid relational tables, invalid conditions, etc.), invalid query processing can make Invalid query discarde it instead of taking further action in the initial stages. So, the query processing efficiency will be improved; 3)The storage structure node of the Query Plan Tree has been improved by the reduction of the original five properties to three. The space consumption to create the query plan tree has been reduced; 4) It also designed a semantic caching query processing experimental model and the simulation experiments have been carried out to the single chip and multiple cache-chip cache query processing. The experimental result has proved the correctness and effectiveness of the semantic caching query processing strategies and algorithms.In the aspect of query cutting optimization research, the semantic caching query is practical for its rapid implementation in query cut and its simple cut results. if the check cutting process consumes too much time or the remaining probe queries and the rest query are too complicated, they both will affect the implementation efficiency of query processing and semantic caching utility will also be greatly reduced. In this paper, the time and space consumption and the query cutting results complexity have been reduced. It also gives out the cutting optimization strategies based on the logical rules. the paper includes the following: 1)The thorough analysis on the necessity of the optimization of the semantic caching query processing and the analysis of the optimization theory basis; 2) Analysis of the the possibility to simplify logic operations formula and the proposition of the 12 new optimization rules. at the same time, it has made the predication of the satisfication degree and the optimizing treatment. Therefore, the scale of the query logic formula cut has been significantly reduced and the cut detection query and the remaining queries could be as simple as possible; 3) Conjunction formula optimization algorithm,probe query optimization and the remaining query optimization algorithm was designed; 4)An experimental simulation model was proposed, the simulation performance will contrast the cutting mechanism between the optimized and the unoptimized in time consumption,space consumption,the complexity of the probe query and the remaining query,cache space demand. The experimental result is a good illustration to the effectiveness of the optimization strategy. |
PDF Full Text Request