47,788 research outputs found
Incremental View Maintenance For Collection Programming
In the context of incremental view maintenance (IVM), delta query derivation
is an essential technique for speeding up the processing of large, dynamic
datasets. The goal is to generate delta queries that, given a small change in
the input, can update the materialized view more efficiently than via
recomputation. In this work we propose the first solution for the efficient
incrementalization of positive nested relational calculus (NRC+) on bags (with
integer multiplicities). More precisely, we model the cost of NRC+ operators
and classify queries as efficiently incrementalizable if their delta has a
strictly lower cost than full re-evaluation. Then, we identify IncNRC+; a large
fragment of NRC+ that is efficiently incrementalizable and we provide a
semantics-preserving translation that takes any NRC+ query to a collection of
IncNRC+ queries. Furthermore, we prove that incremental maintenance for NRC+ is
within the complexity class NC0 and we showcase how recursive IVM, a technique
that has provided significant speedups over traditional IVM in the case of flat
queries [25], can also be applied to IncNRC+.Comment: 24 pages (12 pages plus appendix
Multi-Agent Cooperation for Particle Accelerator Control
We present practical investigations in a real industrial controls environment
for justifying theoretical DAI (Distributed Artificial Intelligence) results,
and we discuss theoretical aspects of practical investigations for
accelerator control and operation. A generalized hypothesis is introduced,
based on a unified view of control, monitoring, diagnosis, maintenance and
repair tasks leading to a general method of cooperation for expert systems
by exchanging hypotheses. This has been tested for task and result sharing
cooperation scenarios. Generalized hypotheses also allow us to treat the
repetitive diagnosis-recovery cycle as task sharing cooperation. Problems
with such a loop or even recursive calls between the different agents are
discussed
Secure Querying of Recursive XML Views: A Standard XPath-based Technique
Most state-of-the art approaches for securing XML documents allow users to
access data only through authorized views defined by annotating an XML grammar
(e.g. DTD) with a collection of XPath expressions. To prevent improper
disclosure of confidential information, user queries posed on these views need
to be rewritten into equivalent queries on the underlying documents. This
rewriting enables us to avoid the overhead of view materialization and
maintenance. A major concern here is that query rewriting for recursive XML
views is still an open problem. To overcome this problem, some works have been
proposed to translate XPath queries into non-standard ones, called Regular
XPath queries. However, query rewriting under Regular XPath can be of
exponential size as it relies on automaton model. Most importantly, Regular
XPath remains a theoretical achievement. Indeed, it is not commonly used in
practice as translation and evaluation tools are not available. In this paper,
we show that query rewriting is always possible for recursive XML views using
only the expressive power of the standard XPath. We investigate the extension
of the downward class of XPath, composed only by child and descendant axes,
with some axes and operators and we propose a general approach to rewrite
queries under recursive XML views. Unlike Regular XPath-based works, we provide
a rewriting algorithm which processes the query only over the annotated DTD
grammar and which can run in linear time in the size of the query. An
experimental evaluation demonstrates that our algorithm is efficient and scales
well.Comment: (2011
A Review of integrity constraint maintenance and view updating techniques
Two interrelated problems may arise when updating a database. On one
hand, when an update is applied to the database, integrity constraints
may become violated. In such case, the integrity constraint maintenance
approach tries to obtain additional updates to keep integrity
constraints satisfied. On the other hand, when updates of derived or
view facts are requested, a view updating mechanism must be applied to
translate the update request into correct updates of the underlying base
facts.
This survey reviews the research performed on integrity constraint
maintenance and view updating. It is proposed a general framework to
classify and to compare methods that tackle integrity constraint
maintenance and/or view updating. Then, we analyze some of these methods
in more detail to identify their actual contribution and the main
limitations they may present.Postprint (published version
A Potpourri of Reason Maintenance Methods
We present novel methods to compute changes to materialized
views in logic databases like those used by rule-based reasoners.
Such reasoners have to address the problem of changing axioms in the
presence of materializations of derived atoms. Existing approaches have
drawbacks: some require to generate and evaluate large transformed programs
that are in Datalog - while the source program is in Datalog and
significantly smaller; some recompute the whole extension of a predicate
even if only a small part of this extension is affected by the change.
The methods presented in this article overcome these drawbacks and derive
additional information useful also for explanation, at the price of an
adaptation of the semi-naive forward chaining
Views, Program Transformations, and the Evolutivity Problem in a Functional Language
We report on an experience to support multiple views of programs to solve the
tyranny of the dominant decomposition in a functional setting. We consider two
possible architectures in Haskell for the classical example of the expression
problem. We show how the Haskell Refactorer can be used to transform one view
into the other, and the other way back. That transformation is automated and we
discuss how the Haskell Refactorer has been adapted to be able to support this
automated transformation. Finally, we compare our implementation of views with
some of the literature.Comment: 19 page
Data-driven Soft Sensors in the Process Industry
In the last two decades Soft Sensors established themselves as a valuable alternative to the traditional means for the acquisition of critical process variables, process monitoring and other tasks which are related to process control. This paper discusses characteristics of the process industry data which are critical for the development of data-driven Soft Sensors. These characteristics are common to a large number of process industry fields, like the chemical industry, bioprocess industry, steel industry, etc. The focus of this work is put on the data-driven Soft Sensors because of their growing popularity, already demonstrated usefulness and huge, though yet not completely realised, potential. A comprehensive selection of case studies covering the three most important Soft Sensor application fields, a general introduction to the most popular Soft Sensor modelling techniques as well as a discussion of some open issues in the Soft Sensor development and maintenance and their possible solutions are the main contributions of this work
Type-Based Detection of XML Query-Update Independence
This paper presents a novel static analysis technique to detect XML
query-update independence, in the presence of a schema. Rather than types, our
system infers chains of types. Each chain represents a path that can be
traversed on a valid document during query/update evaluation. The resulting
independence analysis is precise, although it raises a challenging issue:
recursive schemas may lead to infer infinitely many chains. A sound and
complete approximation technique ensuring a finite analysis in any case is
presented, together with an efficient implementation performing the chain-based
analysis in polynomial space and time.Comment: VLDB201
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