Cached Queries Research Articles

Enhanced peer-to-peer anonymity approach for privacy preserving in location-based services

ABSTRACT Nowadays, Location-based services (LBS) are important services that take benefits from the revolution in communications. Nevertheless, user’s privacy is considered as significant challenge that could impede the use of this type of services. Current Privacy-preserving techniques mainly preserve location not query privacy (i.e., query issuer identification). The untrusted LBS provider (adversary) can breach user privacy in case that it has some user background knowledge and caches queries from more than one user in the same anonymity region (group). These types of attacks use users’ profiles and cached queries to predict semantically the issuer of each query. In this paper, a peer-to-peer privacy-preserving model is presented to protect the user privacy against these types of attacks taking into account the users’ profiles and cached queries in the LBS server. Using this model, an inference algorithm for predicating semantically the issuer of each query and her/his underlying location is presented to check the probability that a query privacy could be breached. A set of experiments is performed to check the effectiveness of the proposed privacy-preserving model. The results show that the cached queries with semantic matching affect negatively in breaching the query and location privacy.

An Efficient Indexing Method for Skyline Computations with Partially Ordered Domains

Efficient processing of skyline queries with partially ordered domains has been intensively addressed in recent years. To further reduce the query processing time to support high-responsive applications, the skyline queries that were previously processed with user preferences similar to those of the new query contribute useful candidate result points. Hence, the answered queries can be cached with both their results and the user preferences such that the query processor can rapidly retrieve the result for a new query only from the result sets of cached queries with compatible user preferences. When caching a significant number of queries accumulated over time, it is essential to adopt effective access methods to index the cached queries to retrieve a set of relevant cached queries for facilitating the cache-based skyline query computations. In this paper, we propose an extended depth-first search indexing method (e-DFS for short) for accessing user preference profiles represented by directed acyclic graphs (DAGs), and emphasize the design of the e-DFS encoding that effectively encodes a user preference profile into a low-dimensional feature point which is eventually indexed by an R-tree. We obtain one or more traversal orders for each node in a DAG by traversing it through a modified version of the depth-first search which is utilized to examine the topology structure and dominance relations to measure closeness or similarity. As a result, e-DFS which combines the criteria of similarity evaluation is able to greatly reduce the search space by filtering out most of the irrelevant cached queries such that the query processor can avoid accessing the entire data set to compute the query results. Extensive experiments are presented to demonstrate the performance and utility of our indexing method, which outperforms the baseline planning techniques by reducing 37 percent of the computational time on average.

Caching Support for Skyline Query Processing with Partially Ordered Domains

Existing methods have addressed the issue of handling each individual skyline query performed on data sets with partially ordered domains. However, it is still very challenging to process such queries for on-line applications with low response time. In this paper, we introduce a cache-based framework, called CSS, for further reducing the query processing time to support high-responsive applications. Skyline queries that were previously processed with user preferences similar to those of the current query contribute useful candidate result points. Hence, the answered queries are cached with both their results and user preferences such that the query processor can rapidly retrieve the result for a new query only from the result sets of selected queries with compatible user preferences. We introduce a similarity measure that establishes the level of similarity between the user preferences of a new query and a cached query; hence the system can start with the most similar candidates. Furthermore, if a new query is only partially answerable from the cache, then the query processor utilizes the partial result sets and performs less expensive constraint skyline queries guided by violated preferences. Furthermore, we introduce two access methods for cached queries indexed by their user preferences to only access a set of relevant cached queries for similarity measures. Extensive experiments are presented to demonstrate the performance and utility of our novel approach.

Query Optimization in OODBMS: Identifying Subquery for Query Management

This paper is based on relatively newer approach for query optimization in object databases, which uses query decomposition and cached query results to improve execution a query. Issues that are focused here is fast retrieval and high reuse of cached queries, Decompose Query into Sub query, Decomposition of complex queries into smaller for fast retrieval of result. Here we try to address another open area of query caching like handling wider queries. By using some parts of cached results helpful for answering other queries (wider Queries) and combining many cached queries while producing the result. Multiple experiments were performed to prove the productivity of this newer way of optimizing a query. The limitation of this technique is that it’s useful especially in scenarios where data manipulation rate is very low as compared to data retrieval rate.

CODISC: Collaborative and distributed semantic caching for maximizing cache effectiveness in wireless networks

In wireless mobile ad hoc networks (MANETs), a mobile node would normally acquire data from a data server through an access point by sending the server a request each time it needs data. To reduce the high costs normally associated with accessing remote servers (i.e., outside the MANET), data caching by the mobile nodes can be employed. Several caching techniques for MANETs have been proposed and implemented, including a cooperative scheme that we recently introduced. It employs a directory-based approach in which submitted queries are cached in the MANET to be used subsequently as indexes to corresponding data items (results). When a request is issued, nodes cooperate to find its answer (if it exists) and send it to the requesting node. In this paper, we extend this scheme by semantically comparing each submitted request with all cached queries. The semantic analysis process includes trimming the request into fragments and joining the answers of these fragments to produce the answer of the request. We study the performance of the proposed system both analytically and experimentally, and prove the advantageous features of the system relative to others in terms of query response time, generated traffic, and hit ratio.

View disassembly: A rewrite that extracts portions of views

We explore a new form of view rewrite called view disassembly. The objective is to rewrite views in order to “remove” certain sub-views (or unfoldings) of the view. This becomes pertinent for complex views which may be defined over other views and which may involve union. Such complex views arise necessarily in environments such as data warehousing and mediation over heterogeneous databases. View disassembly can be used for view and query optimization, preserving data security, making use of cached queries and materialized views, and view maintenance. We provide computational complexity results of view disassembly. One question is whether the unfoldings to be removed effectively cover the view, meaning that the disassembled view is effectively the empty view, evaluating to the empty table. We illustrate the complexity to determine when a collection of unfoldings cover the view definition. The problem is NP- hard with respect to the number of unfoldings to remove, but not with respect to the size (complexity) of the view definition. We next consider rewrites optimal in the size of the rewritten (disassembled) view. We prove that this task is NP- hard for a special class of views, but this time NP- hard in a worse way: it is NP- hard this time with respect to the size of the view definition in addition to the number of unfoldings to be removed. In general, we suspect the problem is computationally even harder, and we show that the general problem is in Π 2 p . However, we provide good news too. We identify a pertinent class of unfoldings for which the removal of such unfoldings always results in a simpler disassembled view than the original view itself. We also develop an algorithm that finds rewrites equivalent to the disassembled view which are, in a sense, locally optimal. The algorithm establishes a cover completion by finding a (minimal) collection of unfoldings of the view that, along with the unfoldings to be removed, covers the original view. This approach is effectively tractable, unlike the search for globally, or absolutely, optimal rewrites. Furthermore, we show that these cover-completion rewrites are preferable to absolutely optimal rewrites in many ways.

Replacement strategies for XQuery caching systems

To improve the query performance over XML documents in a distributed environment, we develop a semantic caching system named ACE-XQ for XQuery queries. ACE-XQ applies innovative query containment and rewriting techniques to answer user queries using cached queries. We also design a fine-grained replacement strategy which records user access statistics at a finer granularity than the complete XML query regions. As a result, less frequently used XML view fragments are replaced to maintain a better utilization of the cache space. Extensive experimental results illustrate the performance improvement achieved by this strategy over the traditional one for a variety of situations.