Synchronization and Caching Solution for Cost-Effective E-Learning in Resource and Bandwidth Constrained Environments

Electronic learning (e-learning) content delivery and accessibility have received significant research attention over years in order to ensure reliability, availability and cost-effectiveness through Information and Communication Technologies (ICTs).The evolvement of mobile computing devices especially smartphones bring prospects in overcoming the inherent limitations of the Internet when accessing web contents.  Among the potential opportunity revealed includes the ability to work offline. Therefore, this study aims to analyze the existing online and offline e-learning systems in order to explore the uniqueness, technical problems and opportunities in this field. In the same vein, this study proposed synchronization and caching approach for cost-effective e-learning content delivery. The proposed approach synchronizes contents from the original server to local database in mobile computing devices in order to deliver contents to learners in a reliable, cost-effective and timely manner. Finally, comparing existing web-based learning system and the proposed approach, the analyzed results provide empirical evidence that, the proposed approach is significant for bandwidth usage cost saving and hence cost-effectiveness due to ability of working offline. Therefore, synchronization and caching approach cut down several limitations in existing e-learning systems including:  reduction of cost of bandwidth usage; improving system performance by cutting down the servers’ workload and internet usage overheads; cutting down costs of purchasing hardware and increasing motivation in learning activities by allowing learners to access learning contents anywhere and anytime. Keywords: synchronization and caching, e-learning, cost-effectiveness, content delivery, offline

Index ordering by query-independent measures

Conventional approaches to information retrieval search through all applicable entries in an inverted file for a particular collection in order to find those documents with the highest scores. For particularly large collections this may be extremely time consuming. A solution to this problem is to only search a limited amount of the collection at query-time, in order to speed up the retrieval process. In doing this we can also limit the loss in retrieval efficacy (in terms of accuracy of results). The way we achieve this is to firstly identify the most “important” documents within the collection, and sort documents within inverted file lists in order of this “importance”. In this way we limit the amount of information to be searched at query time by eliminating documents of lesser importance, which not only makes the search more efficient, but also limits loss in retrieval accuracy. Our experiments, carried out on the TREC Terabyte collection, report significant savings, in terms of number of postings examined, without significant loss of effectiveness when based on several measures of importance used in isolation, and in combination. Our results point to several ways in which the computation cost of searching large collections of documents can be significantly reduced

Keyword based categorisation of diary entries to support personal Internet content pre-caching on mobile devices

This paper presents a study into the effectiveness of our algorithm for automatic categorisation of real users' diary entries, as a first step towards personal Internet content pre-caching on mobile devices. The study reports an experiment comparing trial subjects allocations of 99 diary entries to those predicted by a keyword-based algorithm. While leaving considerable grounds for improvement, results are positive and show pave the way for supporting mobile services based on categorising users' diary entries

Cache Serializability: Reducing Inconsistency in Edge Transactions

Read-only caches are widely used in cloud infrastructures to reduce access latency and load on backend databases. Operators view coherent caches as impractical at genuinely large scale and many client-facing caches are updated in an asynchronous manner with best-effort pipelines. Existing solutions that support cache consistency are inapplicable to this scenario since they require a round trip to the database on every cache transaction. Existing incoherent cache technologies are oblivious to transactional data access, even if the backend database supports transactions. We propose T-Cache, a novel caching policy for read-only transactions in which inconsistency is tolerable (won't cause safety violations) but undesirable (has a cost). T-Cache improves cache consistency despite asynchronous and unreliable communication between the cache and the database. We define cache-serializability, a variant of serializability that is suitable for incoherent caches, and prove that with unbounded resources T-Cache implements this new specification. With limited resources, T-Cache allows the system manager to choose a trade-off between performance and consistency. Our evaluation shows that T-Cache detects many inconsistencies with only nominal overhead. We use synthetic workloads to demonstrate the efficacy of T-Cache when data accesses are clustered and its adaptive reaction to workload changes. With workloads based on the real-world topologies, T-Cache detects 43-70% of the inconsistencies and increases the rate of consistent transactions by 33-58%.Comment: Ittay Eyal, Ken Birman, Robbert van Renesse, "Cache Serializability: Reducing Inconsistency in Edge Transactions," Distributed Computing Systems (ICDCS), IEEE 35th International Conference on, June~29 2015--July~2 201