11,795 research outputs found
An Algebra of Hierarchical Graphs
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
Requirements modelling and formal analysis using graph operations
The increasing complexity of enterprise systems requires a more advanced
analysis of the representation of services expected than is currently possible.
Consequently, the specification stage, which could be facilitated by formal
verification, becomes very important to the system life-cycle. This paper presents
a formal modelling approach, which may be used in order to better represent
the reality of the system and to verify the awaited or existing system’s properties,
taking into account the environmental characteristics. For that, we firstly propose
a formalization process based upon properties specification, and secondly we
use Conceptual Graphs operations to develop reasoning mechanisms of verifying
requirements statements. The graphic visualization of these reasoning enables us
to correctly capture the system specifications by making it easier to determine if
desired properties hold. It is applied to the field of Enterprise modelling
Improving DISPGB Algorithm Using the Discriminant Ideal
In 1992, V. Weispfenning proved the existence of Comprehensive Groebner Bases
(CGB) and gave an algorithm to compute one. That algorithm was not very
efficient and not canonical. Using his suggestions, A. Montes obtained in 2002
a more efficient algorithm (DISPGB) for Discussing Parametric Groebner Bases.
Inspired in its philosophy, V. Weispfenning defined, in 2002, how to obtain a
Canonical Comprehensive Groebner Basis (CCGB) for parametric polynomial ideals,
and provided a constructive method.
In this paper we use Weispfenning's CCGB ideas to make substantial
improvements on Montes DISPGB algorithm. It now includes rewriting of the
discussion tree using the Discriminant Ideal and provides a compact and
effective discussion. We also describe the new algorithms in the DPGB library
containing the improved DISPGB as well as new routines to check whether a given
basis is a CGB or not, and to obtain a CGB. Examples and tests are also
provided.Comment: 21 pages, see also http://www-ma2.upc.edu/~montes
“Efficiency Flooding”: Black-Box Frontiers and Policy Implications
This research aims to comtribute to the discussion on the importance of theoretically consistent modelling for stochastic efficiency analysis. The robustness of policy suggestions based on inferences from efficiency measures crucially depends on theoretically well-founded estimates. The theoretical consistency of recently published technical efficiency estimates for different sectors and countries is critically reviewed. The results confirm the need for a posteriori checking the regularity of the estimated frontier by the researcher and, if necessary, the a priori imposition of the theoretical requirements.Efficiency Analysis, Functional Form, Mathematical Modelling
Distributive Laws for Monotone Specifications
Turi and Plotkin introduced an elegant approach to structural operational
semantics based on universal coalgebra, parametric in the type of syntax and
the type of behaviour. Their framework includes abstract GSOS, a categorical
generalisation of the classical GSOS rule format, as well as its categorical
dual, coGSOS. Both formats are well behaved, in the sense that each
specification has a unique model on which behavioural equivalence is a
congruence. Unfortunately, the combination of the two formats does not feature
these desirable properties. We show that monotone specifications - that
disallow negative premises - do induce a canonical distributive law of a monad
over a comonad, and therefore a unique, compositional interpretation.Comment: In Proceedings EXPRESS/SOS 2017, arXiv:1709.0004
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