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The research challenge addressed in this paper is to devise effective techniques for identifying <i>task-based sessions</i>, i.e. sets of possibly non contiguous queries issued by the user of a Web Search Engine for carrying out a given <i>task</i>. In order to evaluate and compare different approaches, we built, by means of a manual labeling process, a(More)
This article discusses efficiency and effectiveness issues in caching the results of queries submitted to a Web search engine (WSE). We propose SDC (Static Dynamic Cache), a new caching strategy aimed to efficiently exploit the temporal and spatial locality present in the stream of processed queries. SDC extracts from historical usage data the results of(More)
Web Search Engines provide a large-scale text document retrieval service by processing huge <i>Inverted File</i> indexes. Inverted File indexes allow fast query resolution and good memory utilization since their <i>d</i>-gaps representation can be effectively and efficiently compressed by using variable length encoding methods. This paper proposes and(More)
— This paper presents a new scalable algorithm for discovering closed frequent itemsets, a lossless and condensed representation of all the frequent itemsets that can be mined from a transactional database. Our algorithm exploits a divide-and-conquer approach and a bitwise vertical representation of the database, and adopts a particular visit and(More)
Characteristics of the dataset This short note describes the main characteristics of WebDocs, a huge real-life transactional dataset we made publicly available to the Data Mining community through the FIMI repository. We built WebDocs from a spidered collection of web html documents. The whole collection contains about 1.7 millions documents, mainly written(More)
This paper presents a parallel programming methodology that ensures easy programming, eeciency, and portability of programs to diierent m a c hines belonging to the class of the general-purpose, distributed memory, MIMD architectures. The methodology is based on the deenition of a new, high-level, explicitly parallel language, called P 3 L, and of a set of(More)
Increasingly the datasets used for data mining are becoming huge and physically distributed. Since the distributed knowledge discovery process is both data and computational intensive, the Grid is a natural platform for deploying a high performance data mining service. The focus of this paper is on the core services of such a Grid infrastructure. In(More)
Large-scale Parallel Web Search Engines (WSEs) needs to adopt a strategy for partitioning the inverted index among a set of parallel server nodes. In this paper we are interested in devising an effective term-partitioning strategy, according to which the global vocabulary of terms and the associated inverted lists are split into disjoint subsets, and(More)
One of the main problems raising up in the frequent closed itemsets mining problem is the duplicate detection. In this paper we propose a general technique for promptly detecting and discarding duplicate closed itemsets, without the need of keeping in the main memory the whole set of closed patterns. Our approach can be exploited with substantial(More)