35,762 research outputs found
An Algebra of Hierarchical Graphs and its Application to Structural Encoding
We define an algebraic theory of hierarchical graphs, whose axioms
characterise graph isomorphism: two terms are equated exactly when
they represent the same graph. Our algebra can be understood as
a high-level language for describing graphs with a node-sharing, embedding
structure, and it is then well suited for defining graphical
representations of software models where nesting and linking are key
aspects. In particular, we propose the use of our graph formalism as a
convenient way to describe configurations in process calculi equipped
with inherently hierarchical features such as sessions, locations, transactions,
membranes or ambients. The graph syntax can be seen as an
intermediate representation language, that facilitates the encodings of
algebraic specifications, since it provides primitives for nesting, name
restriction and parallel composition. In addition, proving soundness
and correctness of an encoding (i.e. proving that structurally equivalent
processes are mapped to isomorphic graphs) becomes easier as it can
be done by induction over the graph syntax
A new diagrammatic representation for correlation functions in the in-in formalism
In this paper we provide an alternative method to compute correlation
functions in the in-in formalism, with a modified set of Feynman rules to
compute loop corrections. The diagrammatic expansion is based on an iterative
solution of the equation of motion for the quantum operators with only retarded
propagators, which makes each diagram intrinsically local (whereas in the
standard case locality is the result of several cancellations) and endowed with
a straightforward physical interpretation. While the final result is strictly
equivalent, as a bonus the formulation presented here also contains less graphs
than other diagrammatic approaches to in-in correlation functions. Our method
is particularly suitable for applications to cosmology.Comment: 14 pages, matches the published version. includes a modified version
of axodraw.sty that works with the Revtex4 clas
The lingua franca of Nominalism. Sellars on Leibniz
The paper is not built upon a single central thesis. It has been composed as an attempt to investigate a virtually unexplored theme of inquiry. A kind of historiographical thesis may be put in the following terms: Leibniz can be counted among the remote, but still significant, sources of Sellars's philosophy.
Such thesis, however, is meaningless unless its conceptual relevance is displayed. Therefore, it will be immediately added that Sellars's relation with Leibniz is focused on three main fundamental issues, which respectively concern (1) the concept of nature, (2) the concept of truth and (3) the concept itself of nominalism.
Besides, there are other seemingly minor topics, which actually refers to the definition of abstract entities, of predicates, of proper names and to the datum/factum distinction.
Another challenge the paper is faced with, regards the fact that Sellars does not consider Leibniz only in himself, given that he very often positions him in a close relation to Kant: it is as though there were multifaceted issues brought forward by Leibniz and Kant together forming a complex theoretical unity (over and above their differences). According to Sellars, in fact, they both undermine some of the most solid epistemological principles of the early modern times (mainly founded upon the subject- object lexicon and the idea of veritas as adaequatio rei et intellectus) and they both reshape the meaning of expressions such as \u201cbeing actual\u201d or \u201cbeing true\u201d
Clafer: Lightweight Modeling of Structure, Behaviour, and Variability
Embedded software is growing fast in size and complexity, leading to intimate
mixture of complex architectures and complex control. Consequently, software
specification requires modeling both structures and behaviour of systems.
Unfortunately, existing languages do not integrate these aspects well, usually
prioritizing one of them. It is common to develop a separate language for each
of these facets. In this paper, we contribute Clafer: a small language that
attempts to tackle this challenge. It combines rich structural modeling with
state of the art behavioural formalisms. We are not aware of any other modeling
language that seamlessly combines these facets common to system and software
modeling. We show how Clafer, in a single unified syntax and semantics, allows
capturing feature models (variability), component models, discrete control
models (automata) and variability encompassing all these aspects. The language
is built on top of first order logic with quantifiers over basic entities (for
modeling structures) combined with linear temporal logic (for modeling
behaviour). On top of this semantic foundation we build a simple but expressive
syntax, enriched with carefully selected syntactic expansions that cover
hierarchical modeling, associations, automata, scenarios, and Dwyer's property
patterns. We evaluate Clafer using a power window case study, and comparing it
against other notations that substantially overlap with its scope (SysML, AADL,
Temporal OCL and Live Sequence Charts), discussing benefits and perils of using
a single notation for the purpose
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Supporting Story Synthesis: Bridging the Gap between Visual Analytics and Storytelling
Visual analytics usually deals with complex data and uses sophisticated algorithmic, visual, and interactive techniques. Findings of the analysis often need to be communicated to an audience that lacks visual analytics expertise. This requires analysis outcomes to be presented in simpler ways than that are typically used in visual analytics systems. However, not only analytical visualizations may be too complex for target audience but also the information that needs to be presented. Hence, there exists a gap on the path from obtaining analysis findings to communicating them, which involves two aspects: information and display complexity. We propose a general framework where data analysis and result presentation are linked by story synthesis, in which the analyst creates and organizes story contents. Differently, from the previous research, where analytic findings are represented by stored display states, we treat findings as data constructs. In story synthesis, findings are selected, assembled, and arranged in views using meaningful layouts that take into account the structure of information and inherent properties of its components. We propose a workflow for applying the proposed framework in designing visual analytics systems and demonstrate the generality of the approach by applying it to two domains, social media, and movement analysis
Oblique Matching Pursuit
A method for selecting a suitable subspace for discriminating signal
components through an oblique projection is proposed. The selection criterion
is based on the consistency principle introduced by M. Unser and A. Aldroubi
and extended by Y. Elder. An effective implementation of this principle for the
purpose of subspace selection is achieved by updating of the dual vectors
yielding the corresponding oblique projector.Comment: Last version- as it will appear in IEEE SPL. IEEE Signal Processing
Letters (in press
Interactive visual exploration of a large spatio-temporal dataset: Reflections on a geovisualization mashup
Exploratory visual analysis is useful for the preliminary investigation of large structured, multifaceted spatio-temporal datasets. This process requires the selection and aggregation of records by time, space and attribute, the ability to transform data and the flexibility to apply appropriate visual encodings and interactions. We propose an approach inspired by geographical 'mashups' in which freely-available functionality and data are loosely but flexibly combined using de facto exchange standards. Our case study combines MySQL, PHP and the LandSerf GIS to allow Google Earth to be used for visual synthesis and interaction with encodings described in KML. This approach is applied to the exploration of a log of 1.42 million requests made of a mobile directory service. Novel combinations of interaction and visual encoding are developed including spatial 'tag clouds', 'tag maps', 'data dials' and multi-scale density surfaces. Four aspects of the approach are informally evaluated: the visual encodings employed, their success in the visual exploration of the clataset, the specific tools used and the 'rnashup' approach. Preliminary findings will be beneficial to others considering using mashups for visualization. The specific techniques developed may be more widely applied to offer insights into the structure of multifarious spatio-temporal data of the type explored here
Business Process Visualization - Use Cases, Challenges, Solutions
The proper visualization and monitoring of their (ongoing) business processes is crucial for any enterprise.
Thus a broad spectrum of processes has to be visualized ranging from simple, short–running processes to
complex long–running ones (consisting of up to hundreds of activities). In any case, users shall be able to
quickly understand the logic behind a process and to get a quick overview of related tasks. One practical
problem arises when different fragments of a business process are scattered over several systems where they
are often modeled using different process meta models (e.g., High–Level Petri Nets). The challenge is to find
an integrated and user–friendly visualization for these business processes. In this paper we discover use cases
relevant in this context. Since existing graph layout approaches have focused on general graph drawing so
far we further develop a specific approach for layouting business process graphs. The work presented in this
paper is embedded within a larger project (Proviado) on the visualization of automotive processes
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