165,100 research outputs found
On the theory of composition in physics
We develop a theory for describing composite objects in physics. These can be
static objects, such as tables, or things that happen in spacetime (such as a
region of spacetime with fields on it regarded as being composed of smaller
such regions joined together). We propose certain fundamental axioms which, it
seems, should be satisfied in any theory of composition. A key axiom is the
order independence axiom which says we can describe the composition of a
composite object in any order. Then we provide a notation for describing
composite objects that naturally leads to these axioms being satisfied. In any
given physical context we are interested in the value of certain properties for
the objects (such as whether the object is possible, what probability it has,
how wide it is, and so on). We associate a generalized state with an object.
This can be used to calculate the value of those properties we are interested
in for for this object. We then propose a certain principle, the composition
principle, which says that we can determine the generalized state of a
composite object from the generalized states for the components by means of a
calculation having the same structure as the description of the generalized
state. The composition principle provides a link between description and
prediction.Comment: 23 pages. To appear in a festschrift for Samson Abramsky edited by
Bob Coecke, Luke Ong, and Prakash Panangade
Compressed k2-Triples for Full-In-Memory RDF Engines
Current "data deluge" has flooded the Web of Data with very large RDF
datasets. They are hosted and queried through SPARQL endpoints which act as
nodes of a semantic net built on the principles of the Linked Data project.
Although this is a realistic philosophy for global data publishing, its query
performance is diminished when the RDF engines (behind the endpoints) manage
these huge datasets. Their indexes cannot be fully loaded in main memory, hence
these systems need to perform slow disk accesses to solve SPARQL queries. This
paper addresses this problem by a compact indexed RDF structure (called
k2-triples) applying compact k2-tree structures to the well-known
vertical-partitioning technique. It obtains an ultra-compressed representation
of large RDF graphs and allows SPARQL queries to be full-in-memory performed
without decompression. We show that k2-triples clearly outperforms
state-of-the-art compressibility and traditional vertical-partitioning query
resolution, remaining very competitive with multi-index solutions.Comment: In Proc. of AMCIS'201
A Universal Characterization of the Double Powerlocale
This is a version from 29 Sept 2003 of the paper published under the same name in Theoretical Computer Science 316 (2004) 297{321.
The double powerlocale P(X) (found by composing, in either order,the upper and lower powerlocale constructions PU and PL) is shown to be isomorphic in [Locop; Set] to the double exponential SSX where S is the Sierpinski locale. Further PU(X) and PL(X) are shown to be the subobjects P(X) comprising, respectively, the meet semilattice and join
semilattice homomorphisms. A key lemma shows that, for any locales X and Y , natural transformations from SX (the presheaf Loc
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