Adding DL-Lite TBoxes to Proper Knowledge Bases

Levesque’s proper knowledge bases (proper KBs) correspond to infinite sets of ground positive and negative facts, with the notable property that for FOL formulas in a certain normal form, which includes conjunctive queries and positive queries possibly extended with a controlled form of negation, entailment reduces to formula evaluation. However proper KBs represent extensional knowledge only. In description logic terms, they correspond to ABoxes. In this paper, we augment them with DL-Lite TBoxes, expressing intensional knowledge (i.e., the ontology of the domain). DL-Lite has the notable property that conjunctive query answering over TBoxes and standard description logic ABoxes is re- ducible to formula evaluation over the ABox only. Here, we investigate whether such a property extends to ABoxes consisting of proper KBs. Specifically, we consider two DL-Lite variants: DL-Literdfs , roughly corresponding to RDFS, and DL-Lite_core , roughly corresponding to OWL 2 QL. We show that when a DL- Lite_rdfs TBox is coupled with a proper KB, the TBox can be compiled away, reducing query answering to evaluation on the proper KB alone. But this reduction is no longer possible when we associate proper KBs with DL-Lite_core TBoxes. Indeed, we show that in the latter case, query answering even for conjunctive queries becomes coNP-hard in data complexity

Returns to Schooling, Institutions and Heterogeneous Diploma Effects: An Expanded Mincerian Framework applied to Mexico

We hypothesize two sources for sheepskin effects--signaling, and diplomas tied to jobs with downwards rigid wages. These theories have implications for diploma effects not only in the first, but also the second moments of the Mincerian earnings distribution that we are able to identify using a flexible econometric specification. Idiosyncrasies in Mexican labor market and educational institutions offer a natural experiment on which to train this methodology and test these theories. Correcting for heterogeneity in diplomas, we find no evidence of sheepskin effects, except on graduation from primary school. We find compelling evidence that returns to education (in both moments) are linked with labor market institutions and job-specific diplomas in the manner we hypothesize. Our econometric structure corrects for sample selectivity due to unemployment and allows us to observe behavior on the quantity axis of a labor market segmented by sheepskin effects. We also analyze the covariates of hours worked which helps to explain observed patterns in hourly earnings.

Galaxies infalling into groups: filaments vs. isotropic infall

We perform a comparative analysis of the properties of galaxies infalling into groups classifying them accordingly to whether they are: falling along filamentary structures; or they are falling isotropically. For this purpose, we identify filamentary structures connecting massive groups of galaxies in the SDSS. We perform a comparative analysis of some properties of galaxies in filaments, in the isotropic infall region, in the field, and in groups. We study the luminosity functions (LF) and the dependence of the specific star formation rate (SSFR) on stellar mass, galaxy type, and projected distance to the groups that define the filaments. We find that the LF of galaxies in filaments and in the isotropic infalling region are basically indistinguishable between them, with the possible exception of late-type galaxies. On the other hard, regardless of galaxy type, their LFs are clearly different from that of field or group galaxies. Both of them have characteristic absolute magnitudes and faint end slopes in between the field and group values. More significant differences between galaxies in filaments and in the isotropic infall region are observed when we analyse the SSFR. We find that galaxies in filaments have a systematically higher fraction of galaxies with low SSFR as a function of both, stellar mass and distance to the groups, indicating a stronger quenching of the star formation in the filaments compared to both, the isotropic infalling region, and the field. Our results suggest that some physical mechanisms that determine the differences observed between field galaxies and galaxies in systems, affect galaxies even when they are not yet within the systems.Comment: Accepted in MNRAS, 10 pages, 8 figure

Inequality and Heterogeneous Returns to Education in Mexico (1992-2002)

Within the attempts to understand Mexican economic inequality, returns to education have received a great deal of attention. The driving question has been: why are Mexican wages so unequal? This paper argues that not only the distribution of human capital matters, but also sociodemographic variables, which have their own dynamics and complex interactions with the former. A three-equation maximum likelihood specification in which employment, hours worked and log-wages, as well as their joint variance matrix is proposed, generalizing the Mincerian specification. The resulting is a complex story, where income profiles depend upon particular characteristics.