102 research outputs found
View Selection in Semantic Web Databases
We consider the setting of a Semantic Web database, containing both explicit
data encoded in RDF triples, and implicit data, implied by the RDF semantics.
Based on a query workload, we address the problem of selecting a set of views
to be materialized in the database, minimizing a combination of query
processing, view storage, and view maintenance costs. Starting from an existing
relational view selection method, we devise new algorithms for recommending
view sets, and show that they scale significantly beyond the existing
relational ones when adapted to the RDF context. To account for implicit
triples in query answers, we propose a novel RDF query reformulation algorithm
and an innovative way of incorporating it into view selection in order to avoid
a combinatorial explosion in the complexity of the selection process. The
interest of our techniques is demonstrated through a set of experiments.Comment: VLDB201
RDFViewS: A Storage Tuning Wizard for RDF Applications
In recent years, the significant growth of RDF data used in numerous
applications has made its efficient and scalable manipulation an important
issue. In this paper, we present RDFViewS, a system capable of choosing the
most suitable views to materialize, in order to minimize the query response
time for a specific SPARQL query workload, while taking into account the view
maintenance cost and storage space constraints. Our system employs practical
algorithms and heuristics to navigate through the search space of potential
view configurations, and exploits the possibly available semantic information -
expressed via an RDF Schema - to ensure the completeness of the query
evaluation
The ViP2P Platform: XML Views in P2P
The growing volumes of XML data sources on the Web or produced by
enterprises, organizations etc. raise many performance challenges for data
management applications. In this work, we are concerned with the distributed,
peer-to-peer management of large corpora of XML documents, based on distributed
hash table (or DHT, in short) overlay networks. We present ViP2P (standing for
Views in Peer-to-Peer), a distributed platform for sharing XML documents based
on a structured P2P network infrastructure (DHT). At the core of ViP2P stand
distributed materialized XML views, defined by arbitrary XML queries, filled in
with data published anywhere in the network, and exploited to efficiently
answer queries issued by any network peer. ViP2P allows user queries to be
evaluated over XML documents published by peers in two modes. First, a
long-running subscription mode, when a query can be registered in the system
and receive answers incrementally when and if published data matches the query.
Second, queries can also be asked in an ad-hoc, snapshot mode, where results
are required immediately and must be computed based on the results of other
long-running, subscription queries. ViP2P innovates over other similar
DHT-based XML sharing platforms by using a very expressive structured XML query
language. This expressivity leads to a very flexible distribution of XML
content in the ViP2P network, and to efficient snapshot query execution. ViP2P
has been tested in real deployments of hundreds of computers. We present the
platform architecture, its internal algorithms, and demonstrate its efficiency
and scalability through a set of experiments. Our experimental results outgrow
by orders of magnitude similar competitor systems in terms of data volumes,
network size and data dissemination throughput.Comment: RR-7812 (2011
Kaskade: Graph Views for Efficient Graph Analytics
Graphs are an increasingly popular way to model real-world entities and
relationships between them, ranging from social networks to data lineage graphs
and biological datasets. Queries over these large graphs often involve
expensive subgraph traversals and complex analytical computations. These
real-world graphs are often substantially more structured than a generic
vertex-and-edge model would suggest, but this insight has remained mostly
unexplored by existing graph engines for graph query optimization purposes.
Therefore, in this work, we focus on leveraging structural properties of graphs
and queries to automatically derive materialized graph views that can
dramatically speed up query evaluation. We present KASKADE, the first graph
query optimization framework to exploit materialized graph views for query
optimization purposes. KASKADE employs a novel constraint-based view
enumeration technique that mines constraints from query workloads and graph
schemas, and injects them during view enumeration to significantly reduce the
search space of views to be considered. Moreover, it introduces a graph view
size estimator to pick the most beneficial views to materialize given a query
set and to select the best query evaluation plan given a set of materialized
views. We evaluate its performance over real-world graphs, including the
provenance graph that we maintain at Microsoft to enable auditing, service
analytics, and advanced system optimizations. Our results show that KASKADE
substantially reduces the effective graph size and yields significant
performance speedups (up to 50X), in some cases making otherwise intractable
queries possible
Viewing a World of Annotations through AnnoVIP
National audienceLe développement de contenus en format numériques a conduit à l'apparition de corpus de documents structurés interconnectés (tels que les pages HTML ou XML) et d'annotations sémantiques, typiquement exprimées en RDF, qui rajoutent des informations sur ces documents. Les annotations sont souvent produites indépendamment des documents. Nous présentons AnnoVIP, une plateforme pair-à -pair capable d'exploiter de manière efficace un corpus de documents annotés, s'appuyant sur un nouveau modèle de vues matérialisées XML, déployées en pair-à -pair
Late Onset of Severe Symptoms in a Patient with Wolff-Parkinson-White Syndrome with Misleading ECG Pattern of the Accessory Pathway Origin Undergoing Successful Ablation
The case of a female patient with symptomatic Wolff-Parkinson-White syndrome is presented with very late onset of symptoms at the age of 65 years, who had an apparent left-sided posteroseptal accessory pathway, which was ablated via a right-sided approach. A subepicardial location was strongly suspected within the coronary sinus ostium at the origin of the middle cardiac vein by applying both ECG and fluoroscopic criteria. Rhythmos 2016;11(3):73-75.
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