6,179 research outputs found
State-of-the-art on evolution and reactivity
This report starts by, in Chapter 1, outlining aspects of querying and updating resources on
the Web and on the Semantic Web, including the development of query and update languages
to be carried out within the Rewerse project.
From this outline, it becomes clear that several existing research areas and topics are of
interest for this work in Rewerse. In the remainder of this report we further present state of
the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give
an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs;
in Chapter 4 event-condition-action rules, both in the context of active database systems and
in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks
Applying Formal Methods to Networking: Theory, Techniques and Applications
Despite its great importance, modern network infrastructure is remarkable for
the lack of rigor in its engineering. The Internet which began as a research
experiment was never designed to handle the users and applications it hosts
today. The lack of formalization of the Internet architecture meant limited
abstractions and modularity, especially for the control and management planes,
thus requiring for every new need a new protocol built from scratch. This led
to an unwieldy ossified Internet architecture resistant to any attempts at
formal verification, and an Internet culture where expediency and pragmatism
are favored over formal correctness. Fortunately, recent work in the space of
clean slate Internet design---especially, the software defined networking (SDN)
paradigm---offers the Internet community another chance to develop the right
kind of architecture and abstractions. This has also led to a great resurgence
in interest of applying formal methods to specification, verification, and
synthesis of networking protocols and applications. In this paper, we present a
self-contained tutorial of the formidable amount of work that has been done in
formal methods, and present a survey of its applications to networking.Comment: 30 pages, submitted to IEEE Communications Surveys and Tutorial
Typing linear algebra : a biproduct-oriented approach
Interested in formalizing the generation of fast running code for linear algebra applications, the authors show how an index-free, calculational approach to matrix algebra can be developed by regarding matrices as morphisms of a category with biproducts. This shifts the traditional view of matrices as indexed structures to a type-level perspective analogous to that of the pointfree algebra of programming. The derivation of fusion, cancellation and abide laws from the biproduct equations makes it easy to calculate algorithms implementing matrix multiplication, the central operation of matrix algebra, ranging from its divide-and-conquer version to its vectorization implementation.
From errant attempts to learn how particular products and coproducts emerge from biproducts, not only blocked matrix algebra is rediscovered but also a way of extending other operations (e.g. Gaussian elimination) blockwise, in a calculational style, is found.
The prospect of building biproduct-based type checkers for computer algebra systems such as MatlabTM is also considered.Fundação para a Ciência e a Tecnologia (FCT
Provenance for Aggregate Queries
We study in this paper provenance information for queries with aggregation.
Provenance information was studied in the context of various query languages
that do not allow for aggregation, and recent work has suggested to capture
provenance by annotating the different database tuples with elements of a
commutative semiring and propagating the annotations through query evaluation.
We show that aggregate queries pose novel challenges rendering this approach
inapplicable. Consequently, we propose a new approach, where we annotate with
provenance information not just tuples but also the individual values within
tuples, using provenance to describe the values computation. We realize this
approach in a concrete construction, first for "simple" queries where the
aggregation operator is the last one applied, and then for arbitrary (positive)
relational algebra queries with aggregation; the latter queries are shown to be
more challenging in this context. Finally, we use aggregation to encode queries
with difference, and study the semantics obtained for such queries on
provenance annotated databases
Greedy and dynamic programming by calculation
Dissertação mestrado integrado em Informatics EngineeringThe mathematical study of the greedy algorithm provides a blueprint for the study of Dynamic Programming (DP),
whose body of knowledge is largely unorganized, remaining obscure to a large part of the software engineering
community. This study aims to structure this body of knowledge, narrowing the gap between a purely examplebased
approach to DP and its scientific foundations. To that effect, matroid theory is leveraged through a pointfree
relation algebra, which is applied to greedy and DP problems. A catalogue of such problems is compiled, and a
broad characterization of DP algorithms is given. Alongside, the theory underlying the thinning relational operator
is explored.O estudo matemático do algoritmo ganancioso («greedy») serve como guia para o estudo da programação
dinâmica, cujo corpo de conhecimento permanece desorganizado e obscuro a uma grande parte da comunidade
de engenharia de software. Este estudo visa estruturar esse corpo de conhecimento, fazendo a ponte entre a
abordagem popular baseada em exemplos e os métodos mais teóricos da literatura científica. Para esse efeito,
a teoria dos matroides é explorada pelo uso de uma álgebra de relações pointfree, e aplicada a problemas
«greedy» e de programação dinâmica. Um catálogo de tais problemas é compilado, e é feita uma caraterização
geral de algoritmos de programação dinâmica. Em paralelo, é explorada a teoria do combinador relacional de
«thinning».This work is financed by National Funds through the Portuguese funding agency, FCT - Fundação para a
Ciência e a Tecnologia, within project UIDB/50014/202
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