218 research outputs found
Database Queries that Explain their Work
Provenance for database queries or scientific workflows is often motivated as
providing explanation, increasing understanding of the underlying data sources
and processes used to compute the query, and reproducibility, the capability to
recompute the results on different inputs, possibly specialized to a part of
the output. Many provenance systems claim to provide such capabilities;
however, most lack formal definitions or guarantees of these properties, while
others provide formal guarantees only for relatively limited classes of
changes. Building on recent work on provenance traces and slicing for
functional programming languages, we introduce a detailed tracing model of
provenance for multiset-valued Nested Relational Calculus, define trace slicing
algorithms that extract subtraces needed to explain or recompute specific parts
of the output, and define query slicing and differencing techniques that
support explanation. We state and prove correctness properties for these
techniques and present a proof-of-concept implementation in Haskell.Comment: PPDP 201
Nominal Logic Programming
Nominal logic is an extension of first-order logic which provides a simple
foundation for formalizing and reasoning about abstract syntax modulo
consistent renaming of bound names (that is, alpha-equivalence). This article
investigates logic programming based on nominal logic. We describe some typical
nominal logic programs, and develop the model-theoretic, proof-theoretic, and
operational semantics of such programs. Besides being of interest for ensuring
the correct behavior of implementations, these results provide a rigorous
foundation for techniques for analysis and reasoning about nominal logic
programs, as we illustrate via examples.Comment: 46 pages; 19 page appendix; 13 figures. Revised journal submission as
of July 23, 200
A dependent nominal type theory
Nominal abstract syntax is an approach to representing names and binding
pioneered by Gabbay and Pitts. So far nominal techniques have mostly been
studied using classical logic or model theory, not type theory. Nominal
extensions to simple, dependent and ML-like polymorphic languages have been
studied, but decidability and normalization results have only been established
for simple nominal type theories. We present a LF-style dependent type theory
extended with name-abstraction types, prove soundness and decidability of
beta-eta-equivalence checking, discuss adequacy and canonical forms via an
example, and discuss extensions such as dependently-typed recursion and
induction principles
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Raptor wing morphing with flight speed
In gliding flight, birds morph their wings and tails to control their flight trajectory and speed. Using high-resolution videogrammetry, we reconstructed accurate and detailed three-dimensional geometries of gliding flights for three raptors (barn owl, Tyto alba; tawny owl, Strix aluco, and goshawk, Accipiter gentilis). Wing shapes were highly repeatable and shoulder actuation was a key component of reconfiguring the overall planform and controlling angle of attack. The three birds shared common spanwise patterns of wing twist, an inverse relationship between twist and peak camber, and held their wings depressed below their shoulder in an anhedral configuration. With increased speed, all three birds tended to reduce camber throughout the wing, and their wings bent in a saddle-shape pattern. A number of morphing features suggest that the coordinated movements of the wing and tail support efficient flight, and that the tail may act to modulate wing camber through indirect aeroelastic control
A Practical Theory of Language-integrated Query
Language-integrated query is receiving renewed attention, in part because of its support through Microsoft’s LINQ framework. We present a practical theory of language-integrated query based on quotation and normalisation of quoted terms. Our technique supports join queries, abstraction over values and predicates, composition of queries, dynamic generation of queries, and queries with nested intermediate data. Higher-order features prove useful even for constructing first-order queries. We prove a theorem characterising when a host query is guaranteed to generate a single SQL query. We present experimental results confirming our technique works, even in situations where Microsoft’s LINQ framework either fails to produce an SQL query or, in one case, produces an avalanche of SQL queries
Myosin-I nomenclature
We suggest that the vertebrate myosin-I field adopt a common nomenclature system based on the names adopted by the Human Genome Organization (HUGO). At present, the myosin-I nomenclature is very confusing; not only are several systems in use, but several different genes have been given the same name. Despite their faults, we believe that the names adopted by the HUGO nomenclature group for genome annotation are the best compromise, and we recommend universal adoption
The Evolution of Fangs, Venom, and Mimicry Systems in Blenny Fishes
Venom systems have evolved on multiple occasions
across the animal kingdom, and they can act as key
adaptations to protect animals from predators.
Consequently, venomous animals serve as models
for a rich source of mimicry types, as non-venomous
species benefit from reductions in predation risk by
mimicking the coloration, body shape, and/or movement
of toxic counterparts. The frequent evolution
of such deceitful imitations provides notable
examples of phenotypic convergence and are often
invoked as classic exemplars of evolution by natural
selection. Here, we investigate the evolution of fangs,
venom, and mimetic relationships in reef fishes from
the tribe Nemophini (fangblennies). Comparative
morphological analyses reveal that enlarged canine
teeth (fangs) originated at the base of the Nemophini
radiation and have enabled a micropredatory feeding
strategy in non-venomous Plagiotremus spp. Subsequently,
the evolution of deep anterior grooves and
their coupling to venom secretory tissue provide
Meiacanthus spp. with toxic venom that they effectively
employ for defense. We find that fangblenny
venom contains a number of toxic components that
have been independently recruited into other animal
venoms, some of which cause toxicity via interactions
with opioid receptors, and result in a multifunctional
biochemical phenotype that exerts potent hypotensive
effects. The evolution of fangblenny venom has
seemingly led to phenotypic convergence via the formation
of a diverse array of mimetic relationships that
provide protective (Batesian mimicry) and predatory
(aggressive mimicry) benefits to other fishes.
Our results further our understanding of how novel
morphological and biochemical adaptations stimulate
ecological interactions in the natural world
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