In this paper, we present a novel approach called WaterFowl for the storage of RDF triples that addresses some key issues in the contexts of big data and the Semantic Web. The architecture of our prototype, largely based on the use of succinct data structures, enables the representation of triples in a self-indexed, compact manner without requiring decompression at query answering time. Moreover, it is adapted to eciently support RDF and RDFS entailment regimes thanks to an optimized encoding of ontology concepts and properties that does not require a complete inference materialization or extensive query rewriting algorithms. This approach implies to make a distinction between the terminological and the assertional components of the knowledge base early in the process of data preparation, i:e:, preprocessing the data before storing it in our structures. The paper describes the complete architecture of this system and presents some preliminary results obtained from evaluations conducted on our rst prototype.
Our approach is inspired from the HDT @cite_6 solution which mainly focuses on data exchange (and thus on data compression). Its former motivation was to support the exchange of large data sets highly compressed using SDS. Later, @cite_0 presented HDT FoQ, an extension of the structure of HDT that enables some simple data retrieving operations. Nevertheless, this last contribution was not allowing any form of reasoning nor was providing methods the query the data sets. In fact, WaterFowl brings the HDT FoQ approach further to its logical conclusion by using a pair of wavelet trees in the object layer (HDT FoQ uses an adjacency list for this layer) and by integrating a complete query processing solution with complete RDFS reasoning (, handling any inference using RDFS expressiveness). This is made possible by an adaptation of both the dictionary and the triple structures. Note that this adaptation enables to retain the nice compression properties of HDT FoQ (see Section 5).
@cite_0 @cite_6
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Huge RDF datasets are currently exchanged on textual RDF formats, hence consumers need to post-process them using RDF stores for local consumption, such as indexing and SPARQL query. This results in a painful task requiring a great effort in terms of time and computational resources. A first approach to lightweight data exchange is a compact (binary) RDF serialization format called HDT . In this paper, we show how to enhance the exchanged HDT with additional structures to support some basic forms of SPARQL query resolution without the need of "unpacking" the data. Experiments show that i) with an exchanging efficiency that outperforms universal compression, ii) post-processing now becomes a fast process which iii) provides competitive query performance at consumption. Increasingly huge RDF data sets are being published on the Web. Currently, they use different syntaxes of RDF, contain high levels of redundancy and have a plain indivisible structure. All this leads to fuzzy publications, inefficient management, complex processing and lack of scalability. This paper presents a novel RDF representation (HDT) which takes advantage of the structural properties of RDF graphs for splitting and representing, efficiently, three components of RDF data: Header, Dictionary and Triples structure. On-demand management operations can be implemented on top of HDT representation. Experiments show that data sets can be compacted in HDT by more than fifteen times the current naive representation, improving parsing and processing while keeping a consistent publication scheme. For exchanging, specific compression techniques over HDT improve current compression solutions.