Modeling Adoption and Usage of Competing Products

The emergence and wide-spread use of online social networks has led to a dramatic increase on the availability of social activity data. Importantly, this data can be exploited to investigate, at a microscopic level, some of the problems that have captured the attention of economists, marketers and sociologists for decades, such as, e.g., product adoption, usage and competition. In this paper, we propose a continuous-time probabilistic model, based on temporal point processes, for the adoption and frequency of use of competing products, where the frequency of use of one product can be modulated by those of others. This model allows us to efficiently simulate the adoption and recurrent usages of competing products, and generate traces in which we can easily recognize the effect of social influence, recency and competition. We then develop an inference method to efficiently fit the model parameters by solving a convex program. The problem decouples into a collection of smaller subproblems, thus scaling easily to networks with hundred of thousands of nodes. We validate our model over synthetic and real diffusion data gathered from Twitter, and show that the proposed model does not only provides a good fit to the data and more accurate predictions than alternatives but also provides interpretable model parameters, which allow us to gain insights into some of the factors driving product adoption and frequency of use

Submodular Inference of Diffusion Networks from Multiple Trees

Diffusion and propagation of information, influence and diseases take place over increasingly larger networks. We observe when a node copies information, makes a decision or becomes infected but networks are often hidden or unobserved. Since networks are highly dynamic, changing and growing rapidly, we only observe a relatively small set of cascades before a network changes significantly. Scalable network inference based on a small cascade set is then necessary for understanding the rapidly evolving dynamics that govern diffusion. In this article, we develop a scalable approximation algorithm with provable near-optimal performance based on submodular maximization which achieves a high accuracy in such scenario, solving an open problem first introduced by Gomez-Rodriguez et al (2010). Experiments on synthetic and real diffusion data show that our algorithm in practice achieves an optimal trade-off between accuracy and running time.Comment: To appear in the 29th International Conference on Machine Learning (ICML), 2012. Website: http://www.stanford.edu/~manuelgr/network-inference-multitree

An Integrated Semantic Web Service Discovery and Composition Framework

In this paper we present a theoretical analysis of graph-based service composition in terms of its dependency with service discovery. Driven by this analysis we define a composition framework by means of integration with fine-grained I/O service discovery that enables the generation of a graph-based composition which contains the set of services that are semantically relevant for an input-output request. The proposed framework also includes an optimal composition search algorithm to extract the best composition from the graph minimising the length and the number of services, and different graph optimisations to improve the scalability of the system. A practical implementation used for the empirical analysis is also provided. This analysis proves the scalability and flexibility of our proposal and provides insights on how integrated composition systems can be designed in order to achieve good performance in real scenarios for the Web.Comment: Accepted to appear in IEEE Transactions on Services Computing 201

The Epistemic Control Loop

In the ICEA project we are concerned with the extraction of general designs from rat brains

Productivity and Quality-Environmental Changes in Marketing Co-operatives: An Analysis on the Horticultural Sector

The object of the present paper is to analyse productivity incorporating quality-environmental changes in marketing co-operatives. Firstly, it reviews competitiveness factors in the current European agri-food market, especially in relation to the fruit and vegetables sector. Secondly, the productivity trend is studied empirically using nonparametric methods (Malmquist indices) and taking as reference panel data of Andalusian horticultural co-operatives for the period 1994-2001. For this purpose productivity is decomposed into technological change, efficiency and quality-environmental change. Additionally, the correlation of these results with other economic variables is analysed. The indicators obtained show a relevant increase in efficiency for the period under study and a high relationship between the results and product quality-environmental improvement.productivity, quality-environment, efficiency, marketing co-operative, horticultural sector, Agribusiness, Productivity Analysis, D24, Q13, Q21, L15,

Productivity and Environmental Performance in Marketing Cooperatives: Incentive Schemes on the Horticultural Sector

The object of the present paper is to analyze the productivity of marketing cooperatives incorporating environmental inputs/outputs. In the European agricultural policy, expectations for attaining sustainable and competitive agriculture lie to a great extent on the cooperative sector's ability to adapt to the new market conditions. These challenges have led marketing cooperatives in the fruit and vegetables sector to consider improvement in productivity and sound environmental performance. In this sector environmental management was intensified by the Common Agrarian Policy (CAP) through incentives on the so-called Operative Programs (OP). The present study analyses the total factor productivity (TFP) related to environmental variables in this sector using a parametric-stochastic approach and taking as reference a panel data of Spanish cooperatives for the period 1994-2002. Additionally, the determinants of productivity environmental indices are examined econ ometrically. The estimates obtained show a relevant increase in the efficiency component for the period under study and a relatively low impact of incentive schemes. However, they also show a relationship between productivity changes and several management factors in cooperatives, such as labor quality, capital intensity and environmental spillover.Productivity, environmental performance, parametric approach, efficiency, marketing cooperative, horticultural sector, Agribusiness, Environmental Economics and Policy, Productivity Analysis, D24, Q13, Q21, L15,