Allocating Planning Effort When Actions Expire

Making plans that depend on external events can be tricky. For example, an agent considering a partial plan that involves taking a bus must recognize that this partial plan is only viable if completed and selected for execution in time for the agent to arrive at the bus stop. This setting raises the thorny problem of allocating the agent’s planning effort across multiple open search nodes, each of which has an expiration time and an expected completion effort in addition to the usual estimated plan cost. This paper formalizes this metareasoning problem, studies its theoretical properties, and presents several algorithms for solving it. Our theoretical results include a surprising connection to job scheduling, as well as to deliberation scheduling in time-dependent planning. Our empirical results indicate that our algorithms are effective in practice. This work advances our understanding of how heuristic search planners might address realistic problem settings.

O desfio de planejar e produzir expansão urbana com qualidade: a experiência colombiana dos planos parciais em Bogotá, Colômbia

Resumo: O artigo discute a necessidade de planejar o crescimento urbano em extensãonas cidades latino-americanas face à exacerbada mercantilização do desenvolvimentourbano que envolve disponibilizar áreas urbanizáveis e atender às estratégias do mercado interessado na dispersão e em ganhos especulativos, nem sempre produzindo espaços comqualidade urbano-ambiental ou dando conta das necessidades habitacionais. Reconhecendoa perversidade desse quadro e admitindo-se que o crescimento em extensão é um padrão recorrente, procurou-se visitar a experiência colombiana que obriga os municípios a planejarema expansão urbana em diversas escalas, articulando plano urbano, execução e investimentos. Este processo centralizador, elaborado essencialmente por técnicos, parece ter tido resultados urbanos: produziu preventivamente novas áreas urbanizadas com qualidade em Bogotá edeixou aos empreendedores privados a construção da habitação. No entanto, manteve algumas características do padrão periférico de crescimento, como a não mescla de classes sociais, a concentração de habitação distante de outros usos ou trabalho.Palavras-chave Bogotá; Colômbia; expansão urbana; planejamento urbano; plano parcial; plano urbano. Abstract: The paper discusses the possibility of planning urban growth in LatinAmerican cities facing the radicalization of urban sprawl, mercantilization of urban landand speculative land markets that seldom produce spaces of quality, neither respond to housing needs. Recognizing this model as inadequate, and assuming that urban growth is a recurring pattern, this paper brings the Colombian experience, which requires municipalities to planurban expansion in many realms, concerning urban plans, implementation and investmentson settlements. This centralized process, developed essentially by experts, seems to have produced positive achievements: produced good quality urbanized areas in Bogota while leaving housing building to private developers. However, some patterns of peripheral growth were mantained,such as social homogeinity and settlements distant from other urban activities.Keywords: Bogota; Colombia; partial plan; urban plan; urban planning;urban sprawl.

ADAPTIVE QUERY OPTIMIZATION IN DYNAMIC DATABASES

This paper addresses the problem of query optimization for databases in which objects frequently change their values. A greedy, adaptive query optimization algorithm is proposed to evaluate relational queries and queries containing complex objects. Rather than contructing a full plan for an access path and executing it, the algorithm constructs a partial plan, executes it, updates the statistics, and constructs a new partial plan. Since a partial plan is constructed based on the latest statistics, the algorithm is adaptive to data modifications and errors from the statistics. It is proved that the algorithm can produce an optimal solution for a class of queries. Furthermore, experiments show that the overhead associated with the algorithm is negligible and the algorithm is efficient for other cases.