Optional Properties Versus Subtyping in Conceptual Modeling: A Theory and Empirical Test

An important feature of many conceptual modeling grammars is the set of constraints they provide to allow analysts to show that real-world things may or may not possess a particular property. In the entity-relationship model, for example, the fact that a thing may not possess a property (the property is optional) can be represented by showing the minimum cardinality of a relationship or an attribute is zero (Batini, Ceri and Navathe 1992). Whether this practice should be followed, however, is a contentious issue because it may obfuscate the semantics of the real-world domain that is being modeled. An alternative approach is to eliminate optional properties from conceptual schema diagrams by using subtypes that have only mandatory properties (Weber and Zhang 1996). A problem with this approach, however, is that it often leads to more complex conceptual schema diagrams because they include more elements to represent the additional subtypes needed

Computer-Aided Specification, Evaluation and Monitoring of Information Systems

One of the crucial issues in specifying requirements for an In formation System is to guarantee the effectiveness and the efficiency of their future implementation. The objectives of the methodology, proposed in the IDA project and presented in this paper, have been: 1. To propose a model and an associated language for a more rigourous specification of Information Systems, 2. To develop among others two complementary software tools allowing the experimental evaluation of this specification, by prototyping and simulation, before to implement it · and, more recently, 3. To outline an automated monitoring of the implemented Information System

State and evolution of the African rainforests between 1990 and 2010

This paper presents a 2005 map of Africa’s rainforests with new levels of spatial and thematic detail, being derived from 250m resolution MODIS data, and having an overall accuracy of 84%. A systematic sample of Landsat images (with supplemental data from equivalent platforms to fill sample gaps) is used to produce a consistent assessment of deforestation between 1990, 2000 and 2010 for West Africa, Central Africa and Madagascar. Net deforestation is estimated at 0.28% yr-1 for the period 1990-2000 and 0.14% yr-1 for the period 2000-2010. West Africa and Madagascar exhibit a much higher deforestation rate than the Congo Basin. Based on a simple analysis of the variance over the Congo Basin, we show that expanding agriculture and increasing fuelwood demands are key drivers of deforestation while well-controlled timber exploitation programmes have little or no direct influence on forest-cover reduction at present. Rural and urban population concentrations and fluxes are identified as strong underlying causes of deforestation in this study.JRC.H.5-Land Resources Managemen

A Dynamical Model of Oocyte Maturation Unveils Precisely Orchestrated Meiotic Decisions

Maturation of vertebrate oocytes into haploid gametes relies on two consecutive meioses without intervening DNA replication. The temporal sequence of cellular transitions driving eggs from G2 arrest to meiosis I (MI) and then to meiosis II (MII) is controlled by the interplay between cyclin-dependent and mitogen-activated protein kinases. In this paper, we propose a dynamical model of the molecular network that orchestrates maturation of Xenopus laevis oocytes. Our model reproduces the core features of maturation progression, including the characteristic non-monotonous time course of cyclin-Cdks, and unveils the network design principles underlying a precise sequence of meiotic decisions, as captured by bifurcation and sensitivity analyses. Firstly, a coherent and sharp meiotic resumption is triggered by the concerted action of positive feedback loops post-translationally activating cyclin-Cdks. Secondly, meiotic transition is driven by the dynamic antagonism between positive and negative feedback loops controlling cyclin turnover. Our findings reveal a highly modular network in which the coordination of distinct regulatory schemes ensures both reliable and flexible cell-cycle decisions

Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches

Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly

Real Exchange Rates and Skills

While most of the literature on the determination of real exchange rates is focused on the role of standard macroeconomic variables, there exists however a few papers that are more concerned by the impact of factors which are usually considered to play a key role in the process of economic development, like demography or inequality. In the present paper, we extend this small branch of the literature by exploring the relationship between labor skills and real exchange rates over the long-run. According to several theoretical arguments, the real exchange rate of countries experiencing an increase in the ratio between skilled and unskilled workers should appreciate. That is what we actually find empirically using panel regressions covering 22 countries over the period 1950-2010. The impact of skills on real exchange rates is robust to the inclusion of several control variables, like those used in traditional analyses of real exchange rates. The real exchange rate therefore appears as one channel through which increases in skills can alter economic growth. What we call a "skill disease" effect offers a new partial explanation to the weak link between human capital and GDP growth that is often found by the empirical literature

Real Exchanges Rates in Commodity Producing Countries: A Reappraisal

Commodity price booms, as those recorded in the last decade, may have a significant economic impact in small, commodity exporting, developing countries. Whether the impact on output is positive or negative is still unclear. It depends on various factors, notably on the impact that commodity prices can have on the real exchange rate of the commodity exporting countries. Two recent papers show that the real exchange rate appreciates when commodity prices increase. Our analysis produces new estimates of this relationship by focusing on a large sample of developing countries which are specialized in the export of one leading commodity. By using non-stationary panel techniques robust to cross-sectional dependence, we find that the price of the dominant commodity has a significant long-run impact on the real exchange rate when the exports of the leading commodity have a share of at least 20 percent in the country's total exports of merchandises. Our results also show that the larger this share, the larger the size of the impact