20,265 research outputs found
Group field theory condensate cosmology: An appetizer
This contribution is an appetizer to the relatively young and fast evolving
approach to quantum cosmology based on group field theory condensate states. We
summarize the main assumptions and pillars of this approach which has revealed
new perspectives on the long-standing question of how to recover the continuum
from discrete geometric building blocks. Among others, we give a snapshot of
recent work on isotropic cosmological solutions exhibiting an accelerated
expansion, a bounce where anisotropies are shown to be under control and
inhomogeneities with an approximately scale-invariant power spectrum. Finally,
we point to open issues in the condensate cosmology approach.Comment: Review article as an invited contribution for the special issue
"Progress in Group Field Theory and Related Quantum Gravity Formalisms",
Universe journa
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
Geospatial Narratives and their Spatio-Temporal Dynamics: Commonsense Reasoning for High-level Analyses in Geographic Information Systems
The modelling, analysis, and visualisation of dynamic geospatial phenomena
has been identified as a key developmental challenge for next-generation
Geographic Information Systems (GIS). In this context, the envisaged
paradigmatic extensions to contemporary foundational GIS technology raises
fundamental questions concerning the ontological, formal representational, and
(analytical) computational methods that would underlie their spatial
information theoretic underpinnings.
We present the conceptual overview and architecture for the development of
high-level semantic and qualitative analytical capabilities for dynamic
geospatial domains. Building on formal methods in the areas of commonsense
reasoning, qualitative reasoning, spatial and temporal representation and
reasoning, reasoning about actions and change, and computational models of
narrative, we identify concrete theoretical and practical challenges that
accrue in the context of formal reasoning about `space, events, actions, and
change'. With this as a basis, and within the backdrop of an illustrated
scenario involving the spatio-temporal dynamics of urban narratives, we address
specific problems and solutions techniques chiefly involving `qualitative
abstraction', `data integration and spatial consistency', and `practical
geospatial abduction'. From a broad topical viewpoint, we propose that
next-generation dynamic GIS technology demands a transdisciplinary scientific
perspective that brings together Geography, Artificial Intelligence, and
Cognitive Science.
Keywords: artificial intelligence; cognitive systems; human-computer
interaction; geographic information systems; spatio-temporal dynamics;
computational models of narrative; geospatial analysis; geospatial modelling;
ontology; qualitative spatial modelling and reasoning; spatial assistance
systemsComment: ISPRS International Journal of Geo-Information (ISSN 2220-9964);
Special Issue on: Geospatial Monitoring and Modelling of Environmental
Change}. IJGI. Editor: Duccio Rocchini. (pre-print of article in press
Interactive Small-Step Algorithms I: Axiomatization
In earlier work, the Abstract State Machine Thesis -- that arbitrary
algorithms are behaviorally equivalent to abstract state machines -- was
established for several classes of algorithms, including ordinary, interactive,
small-step algorithms. This was accomplished on the basis of axiomatizations of
these classes of algorithms. Here we extend the axiomatization and, in a
companion paper, the proof, to cover interactive small-step algorithms that are
not necessarily ordinary. This means that the algorithms (1) can complete a
step without necessarily waiting for replies to all queries from that step and
(2) can use not only the environment's replies but also the order in which the
replies were received
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