The Experts below are selected from a list of 34332 Experts worldwide ranked by ideXlab platform
Richard T. Snodgrass - One of the best experts on this subject based on the ideXlab platform.
-
valid time Indeterminacy in temporal relational databases semantics and representations
IEEE Transactions on Knowledge and Data Engineering, 2013Co-Authors: Luca Anselma, Paolo Terenziani, Richard T. SnodgrassAbstract:Valid-time Indeterminacy is "don't know when" Indeterminacy, coping with cases in which one does not exactly know when a fact holds in the modeled reality. In this paper, we first propose a reference representation (data model and algebra) in which all possible temporal scenarios induced by valid-time Indeterminacy can be extensionally modeled. We then specify a family of 16 more compact representational data models. We demonstrate their correctness with respect to the reference representation and analyze several properties, including their data expressiveness. Then, we compare these compact models along several relevant dimensions. Finally, we also extend the reference representation and a representative of compact representations to cope with probabilities.
-
Supporting valid-time Indeterminacy
ACM Transactions on Database Systems, 1998Co-Authors: Curtis E. Dyreson, Richard T. SnodgrassAbstract:In valid-time Indeterminacy it is known that an event stored in a database did in fact occur, but it is not known exactly when . In this paper we extend the SQL data model and query language to support valid-time Indeterminacy. We represent the occurrence time of an event with a set of possible instants, delimiting when the event might have occurred, and a probability distribution over that set. We also describe query language constructs to retrieve information in the presence of Indeterminacy. These constructs enable users to specify their credibility in the underlying data and their plausibility in the relationships among that data. A denotational semantics for SQL's select statement with optional credibility and plausibility constructs is given. We show that this semantics is reliable, in that it never produces incorrect information, is maximal, in that if it were extended to be more informative, the results may not be reliable, and reduces to the previous semantics when there is no Indeterminacy. Although the extended data model and query language provide needed modeling capabilities, these extensions appear initially to carry a significant execution cost. A contribution of this paper is to demonstrate that our approach is useful and practical. An efficient representation of valid-time Indeterminacy and efficient query processing algorithms are provided. The cost of support for Indeterminacy is empirically measured, and is shown to be modest. Finally, we show that the approach is general, by applying it to the temporal query language constructs being proposed for SQL3.
Nir Jaimovich - One of the best experts on this subject based on the ideXlab platform.
-
income effects and Indeterminacy in a calibrated one sector growth model
Journal of Economic Theory, 2008Co-Authors: Nir JaimovichAbstract:Abstract This note analyzes how the Indeterminacy of competitive equilibrium in one-sector growth models depends on the magnitude of the households' income effect on the demand for leisure. Since I am interested in quantitatively characterizing regions of Indeterminacy, I use the Jaimovich and Rebelo [N. Jaimovich, S. Rebelo, Can news about the future drive the business cycle? Mimeo, Northwestern University, 2007] preferences that span a wide range of income effect values. I find that Indeterminacy can occur for levels of aggregate-returns-to-scale that are well within recent empirical estimates. For these regions of Indeterminacy, the model, when driven solely by sunspot shocks, generates second-moment properties that are consistent with the U.S. data at the business cycle frequency.
-
income effects and Indeterminacy in a calibrated one sector growth model
2007Co-Authors: Nir JaimovichAbstract:This paper analyzes how the Indeterminacy of competitive equilibrium in one-sector growth models depends on the magnitude of the households' income effect on the demand for leisure. The paper first establishes that the presence of income effect is necessary for the existence of an indeterminate equilibrium. I incorporate into this analysis the Jaimovich and Rebelo (2006) preferences that nest the KPR and GHH utility functions and span the entire range of income effect that exists between the two. Having identified these regions of Indeterminacy, I find a lower and an upper bound for the magnitude of income effect that leads to Indeterminacy. Moreover, by allowing for variation in the degree of income effect, I find that Indeterminacy can occur for levels of aggregate-returns-to-scale that are well within recent empirical estimates. Finally, for these regions of Indeterminacy, I simulate the model driven solely by sunspot shocks. I find that the second-moment properties of this model are generally consistent with the U.S. data at the business cycle frequency.
Luca Anselma - One of the best experts on this subject based on the ideXlab platform.
-
valid time Indeterminacy in temporal relational databases semantics and representations
IEEE Transactions on Knowledge and Data Engineering, 2013Co-Authors: Luca Anselma, Paolo Terenziani, Richard T. SnodgrassAbstract:Valid-time Indeterminacy is "don't know when" Indeterminacy, coping with cases in which one does not exactly know when a fact holds in the modeled reality. In this paper, we first propose a reference representation (data model and algebra) in which all possible temporal scenarios induced by valid-time Indeterminacy can be extensionally modeled. We then specify a family of 16 more compact representational data models. We demonstrate their correctness with respect to the reference representation and analyze several properties, including their data expressiveness. Then, we compare these compact models along several relevant dimensions. Finally, we also extend the reference representation and a representative of compact representations to cope with probabilities.
Kazuo Nishimura - One of the best experts on this subject based on the ideXlab platform.
-
Trade and Indeterminacy revisited
International Journal of Economic Theory, 2018Co-Authors: Kazumichi Iwasa, Kazuo Nishimura, Makoto YanoAbstract:We consider a dynamic two‐country model of trade with production externalities with an emphasis on the possibility of global Indeterminacy, which means that the distribution of capital stocks in each country in the long run depends on households’ expectations. Opening trade yields expectation‐driven fluctuations. Global Indeterminacy may occur around the free trade steady states even when the autarkic steady states are saddle points in both countries, and it must happen when local Indeterminacy occurs around the autarkic steady states in both countries.
-
Sunspot Fluctuations in Two-Sector Models with Variable Income Effects
2017Co-Authors: Frédéric Dufourt, Kazuo Nishimura, Carine Nourry, Alain VendittiAbstract:We analyze a version of the Benhabib and Farmer (1996) two-sector model with sector-specific externalities in which we consider a class of utility functions inspired from the one considered in Jaimovich and Rebelo (2009) which is flexible enough to encompass varying degrees of income effect. First, we show that local Indeterminacy and sunspot fluctuations occur in 2-sector models under plausible configurations regarding all structural parameters—in particular regarding the intensity of income effects. Second, we prove that there even exist some configurations for which local Indeterminacy arises under any degree of income effect. More precisely, for any given size of income effect, we show that there is a non-empty range of values for the Frisch elasticity of labor and the elasticity of intertemporal substitution in consumption such that Indeterminacy occurs. This contrasts with the results obtained in one-sector models in both Nishimura et al. (2009), in which it is shown that Indeterminacy cannot occur under either GHH and KPR preferences, and in Jaimovich (2008) in which local Indeterminacy only arises for intermediary income effects.
-
Indeterminacy AND THE ROLE OF FACTOR SUBSTITUTABILITY
Macroeconomic Dynamics, 2004Co-Authors: Kazuo Nishimura, Alain VendittiAbstract:We discuss the role of the elasticity of substitution in the local determinacy properties of a steady state or a stationary balanced growth path in a general multisector economy with CES technologies. Our main results are the following: We give some sufficient conditions for the occurrence of local Indeterminacy in exogenous and endogenous growth models. We show that local Indeterminacy takes place even without a capital intensity reversal from the private to the social level if the productive factors are weakly substitutable. Moreover, we show that the conditions for local Indeterminacy in exogenous growth models and in endogenous growth models may be qualitatively different.
-
Indeterminacy and Sunspots with Constant Returns
Journal of Economic Theory, 1998Co-Authors: Jess Benhabib, Kazuo NishimuraAbstract:Recently there has been a renewed interest in the possibility of Indeterminacy and sunspots, or alternatively put, in the existence of a continuum of equilibria that arises in dynamic economies with some market imperfections. Much of the research in this area has been concerned with the empirical plausibility of Indeterminacy in markets with external effects or with monopolistic competition and which exhibit some degree of increasing returns. While the early results on Indeterminacy relied on relatively large increasing returns and high markups, more recently Benhabib and Farmer (1996a) showed that Indeterminacy can also occur in two-sector models with small sector-specific external effects and very mild increasing returns.
Paolo Terenziani - One of the best experts on this subject based on the ideXlab platform.
-
valid time Indeterminacy in temporal relational databases semantics and representations
IEEE Transactions on Knowledge and Data Engineering, 2013Co-Authors: Luca Anselma, Paolo Terenziani, Richard T. SnodgrassAbstract:Valid-time Indeterminacy is "don't know when" Indeterminacy, coping with cases in which one does not exactly know when a fact holds in the modeled reality. In this paper, we first propose a reference representation (data model and algebra) in which all possible temporal scenarios induced by valid-time Indeterminacy can be extensionally modeled. We then specify a family of 16 more compact representational data models. We demonstrate their correctness with respect to the reference representation and analyze several properties, including their data expressiveness. Then, we compare these compact models along several relevant dimensions. Finally, we also extend the reference representation and a representative of compact representations to cope with probabilities.
