The complexity of acyclic conjunctive queries revisited

In this paper, we consider first-order logic over unary functions and study the complexity of the evaluation problem for conjunctive queries described by such kind of formulas. A natural notion of query acyclicity for this language is introduced and we study the complexity of a large number of variants or generalizations of acyclic query problems in that context (Boolean or not Boolean, with or without inequalities, comparisons, etc...). Our main results show that all those problems are \textit{fixed-parameter linear} i.e. they can be evaluated in time $f(|Q|).|\textbf{db}|.|Q(\textbf{db})|$ where $|Q|$ is the size of the query $Q$, $|\textbf{db}|$ the database size, $|Q(\textbf{db})|$ is the size of the output and $f$ is some function whose value depends on the specific variant of the query problem (in some cases, $f$ is the identity function). Our results have two kinds of consequences. First, they can be easily translated in the relational (i.e., classical) setting. Previously known bounds for some query problems are improved and new tractable cases are then exhibited. Among others, as an immediate corollary, we improve a result of \~\cite{PapadimitriouY-99} by showing that any (relational) acyclic conjunctive query with inequalities can be evaluated in time $f(|Q|).|\textbf{db}|.|Q(\textbf{db})|$. A second consequence of our method is that it provides a very natural descriptive approach to the complexity of well-known algorithmic problems. A number of examples (such as acyclic subgraph problems, multidimensional matching, etc...) are considered for which new insights of their complexity are given.Comment: 30 page

Parallel Deferred Update Replication

Deferred update replication (DUR) is an established approach to implementing highly efficient and available storage. While the throughput of read-only transactions scales linearly with the number of deployed replicas in DUR, the throughput of update transactions experiences limited improvements as replicas are added. This paper presents Parallel Deferred Update Replication (P-DUR), a variation of classical DUR that scales both read-only and update transactions with the number of cores available in a replica. In addition to introducing the new approach, we describe its full implementation and compare its performance to classical DUR and to Berkeley DB, a well-known standalone database

Gift Exchange in the Workplace: Money or Attention?

We develop a model of manager-employee relationships where employees care more for their manager when they are more convinced that their manager cares for them. Managers can signal their altruistic feelings towards their employees in two ways: by offering a generous wage and by giving attention. Contrary to the traditional gift-exchange hypothesis, we show that altruistic managers may offer lower wages and nevertheless build up better social-exchange relationships with their employees than egoistic managers do. In such equilibria, a low wage signals to employees that the manager has something else to offer − namely, a lot of attention − which will induce the employee to stay at the firm and work hard. Our predictions are well in line with some recent empirical findings about gift exchange in the field.gift exchange, sabotage, extra-role behavior, wages, manager-employee relationships, social exchange, conditional altruism, reciprocity, signaling game

Accommodation of Latinos on U of I Campus

What I talk about in my research paper is mainly how Latinos, including my self have accommodated here on the U of I campus. In my personal experience, it was very hard to accommodate, and be around people of other cultures and live in the same building with them. The question is, how did other Latinos here on campus accommodate. did they have trouble accommodate in their dorms? with their roommates? in their classes? or on the campus overall? what did they do to feel welcome? who did they go to if they did had trouble accommodating

Local Public Good Provision, Municipal Consolidation, and National Transfers

We analyze a simple model of local public good provision in a country consisting of a large number of heterogeneous regions, each comprising two districts, a city and a village. When districts remain autonomous and local public goods have positive spillover effects on the neighboring district, there is underprovision of public goods in both the city and the village. When districts consolidate, underprovision persists in the village (and may even become more severe), whereas overprovision of public goods arises in the city as urbanites use their political power to exploit the villagers. From a social welfare point of view, inhabitants of the village have insufficient incentives to vote for consolidation. We examine how national transfers to local governments can resolve these problems

Removing bias due to finite measurement of dynamic systems: case study on P2P systems

Mesurer avec pr\'ecision la dynamique des graphes de terrain est une t\^ache difficile, car les propri\'et\'es observ\'ees peuvent \^etre biais\'ees pour diff\'erentes raisons, en particulier le fait que la p\'eriode de mesure soit finie. Dans ce papier, nous introduisons une m\'ethodologie g\'en\'erale qui nous permet de savoir si la fen\^etre d'observation est suffisamment longue pour caract\'eriser une propri\'et\'e donn\'ee dans n'importe quel syst\`eme dynamique. Nous appliquons cette m\'ethodologie \`a l'\'etude des dur\'ees de sessions et des dur\'ees de vie des fichiers sur deux jeux de donn\'ees P2P. Nous montrons que le comportement des propri\'et\'es est diff\'erent : pour les dur\'ees de sessions, notre m\'ethodologie nous permet de caract\'eriser avec pr\'ecision la forme de leur distribution. Par contre, pour les dur\'ees de vie des fichiers, nous montrons que cette propri\'et\'e ne peut pas \^etre caract\'eris\'ee, soit parce qu'elle n'est pas stationnaire, soit parce que la dur\'ee de notre mesure est trop courte

Social Interaction, Co-Worker Altruism, and Incentives

Social interaction with colleagues is an important job attribute for many workers. To attract and retain workers, managers therefore need to think about how to create and preserve high-quality co-worker relationships. This paper develops a principal-multi-agent model where agents do not only engage in productive activities, but also in social interaction with their colleagues, which in turn creates co-worker altruism. We study how financial incentives for productive activities can improve or damage the work climate. We show that both team incentives and relative incentives can help to create a good work climate.social interaction, altruism, incentive contracts, co-worker satisfaction

Managerial Talent, Motivation, and Self-Selection into Public Management

The quality of public management is a recurrent concern in many countries. Calls to attract the economy’s best and brightest managers to the public sector abound. This paper studies self-selection into managerial positions in the public and private sector, using a model of a perfectly competitive economy where people differ in managerial ability and in public service motivation. We find that, if demand for public sector output is not too high, the equilibrium return to managerial ability is always higher in the private sector. As a result, relatively many of the more able managers self-select into the private sector. Since this outcome is efficient, our analysis implies that attracting a more able managerial workforce to the public sector by increasing remuneration to private-sector levels is not cost-efficient.public management, public service motivation, managerial ability, self-selection

Incentives and the Sorting of Altruistic Agents into Street-Level Bureaucracies

Many street-level bureaucrats (such as caseworkers) have the dual task of helping some clients, while sanctioning others. We develop a model of such a street-level bureaucracy and study the implications of its personnel policy on the self-selection and allocation decisions of agents who differ in altruism towards clients. When bureaucrats are paid flat wages, they do not sanction, and the most altruistic types sort into bureaucracy. Pay-for-performance induces some bureaucrats to sanction, but necessitates an increase in expected wage compensation, which can result in sorting from both the top and bottom of the altruism distribution. We also show how client composition affects sorting and why street-level bureaucrats often experience an overload of clients.street-level bureaucracy, sorting, altruism, personnel policy, pay-for-performance

Interpersonal comparison, status and ambition in organizations

This paper shows that introducing status concerns into a tournament model has substantial implications for the provision of incentives. We emphasize the role of reference groups and determine the optimal number of winners and losers in tournaments. To compensate employees for the disutility of low status, a profit-maximizing employer may be reluctant to demote employees and instead reward workers through promotions. This rationalizes the prevalence of compensation systems which reward winners without explicitly identifying losers. Differences in ambition and ability affect contestants’ efforts and may result in inefficient promotion outcomes. We analyze how to mitigate these inefficiencies when managing a diverse workforce by using mixed and segregated tournament