SHF: Small: An Aspect-Oriented Approach to Large-Scale Urban Simulations

人口、环境和技术的变化正在重塑我们城市环境的基础设施，并将在不久的将来成为关注的焦点。随着替代能源和物联网的出现，突然出现了大量的新技术，这将需要对城市进行重大重组。为了建立健全的公共政策，所有这些新技术都可以从城市模拟中受益匪浅，在政策确定之前衡量它们对城市和人民的影响。大规模的城市模拟往往过于庞大和复杂，无法适应单个机器的资源和单个团队的专业知识。因此，分布式和分散的城市模拟是一种值得开发的技术。不幸的是，分布式模拟仍然很少被使用（除了军事应用）。开发分布式仿真比开发非分布式仿真要困难得多，并且需要更高水平的软件工程专业知识，而建模和仿真专家通常不具备这些专业知识。研究人员和工程师已经知道了这些困难，多年来也有一些努力来解决这些问题。最重要的工作之一是开发高级体系结构（HLA）标准。然而，HLA在实践中的应用一直非常缓慢。调查表明，领域特定的适配器和中间件可以帮助弥合软件知识方面的技术差距。使用适当的软件工程概念和理论可以大大降低开发此类中间件的技术复杂性，并使HLA能够为包括科学家在内的更广泛的受众所使用。本提案的主要目的是研究面向方面编程（AOP）概念的使用是否有助于克服分布式仿真系统所面临的工程挑战。1997年由Kiczales、Lopes等人引入的AOP提出了一种系统分解模型，该模型包含一个基本的功能分解以及一个或多个正交的功能分解，这些功能分解相互交叉。方面的概念（由AOP给出）和城市规划研究人员经常使用的城市方面的一般概念之间有许多相似之处。所有这些方面在概念上是不同的，但在模拟的相同对象，城市及其坐标系统上相互作用。在将AOP范例应用到仿真领域中存在许多未知变量。例如，如果模拟器按方面划分，那么个人、车辆和建筑物等城市实体很有可能是多个模拟器共有的。HLA标准强制一个对象的属性可以被任何模拟器拥有（即读和写权限），但只能被一个模拟器拥有。因此，同一对象的多个方面需要共存，但作为不同的对象。一致性和性能成为维护本质上相同实体的不同版本的问题。确定如何维护方面之间的语义互操作性将解决分布式模拟的一个主要问题。如果AOP被证明非常适合分布式仿真，那么这项工作将对大量建模和仿真专家的分布式仿真的可访问性产生巨大的影响，因此也会对策略制定产生潜在的影响，无论在哪里使用建模和仿真。在科学、物流、社会行为、交通管理、卫生、土地等方面仅举几个例子。

Population, environmental, and technological changes are reshaping the infrastructure of our urban environments, and will be a major focus of attention in the near future. With the advent of alternative energy and the Internet of Things, there is suddenly a plethora of new technologies that will require major restructuring of cities. In order to establish sound public policies, all these new technologies can greatly benefit from urban simulations, to measure their impact on the city and on the people before the policies are defined. Large-scale urban simulations tend to be too large and complex to fit a single machine's resources and a single group's expertise. As such, distributed and decentralized urban simulations are a desirable technology to develop. Unfortunately, distributed simulations are still rarely used (except in military applications). Developing distributed simulations is much harder than developing non-distributed ones, and requires a much higher level of software engineering expertise, which usually modeling and simulation experts do not have. The difficulties have been well-known by researchers and engineers, and over the years there have been a few efforts to address them. One of the most important efforts was the development of the High Level Architecture (HLA) standard. The adoption of HLA in practice, however, has been very slow. Surveys suggest that domain-specific adaptors and middleware could help bridge the technical gap in software knowledge. The use of appropriate software engineering concepts and theories can greatly reduce the technical complexity of developing such middleware, and make HLA accessible to a much wider audience, including scientists.The main objective of this proposal is to investigate whether the use of Aspect Oriented Programming (AOP) concepts will help overcome the engineering challenges faced by distributed simulation systems. Introduced in 1997 by Kiczales, Lopes et. al, AOP put forward a model of system decomposition that encompasses a base functional decomposition as well as one or more orthogonal ones that cut across the base and each other. There are many similarities between the concept of aspect (as given by AOP) and the general concept of aspect of a city that urban planning researchers routinely use. All these aspects are conceptually distinct, but interact with each other over essentially the same objects of simulation, the city and its coordinate system. There are many unknown variables in applying the AOP paradigm to the simulation field. For instance, if simulators are divided by aspects, there is a high chance that urban entities such as individuals, vehicles, and buildings, will be common to multiple simulators. The HLA standard enforces that an attribute of an object can be owned (i.e. read and write permission) by any simulator, but only by one simulator. Thus multiple aspects of the same object will need to coexist, but as different objects. Consistency and performance become issues in maintaining separate versions of what is essentially the same entity. Determining how to maintain a semantic interoperability between aspects would solve one of the major issues with distributed simulations. If AOP proves to be a good fit for distributed simulations, this work can have a tremendous influence on the accessibility of distributed simulations for a large number of modeling and simulation experts, therefore also having a potential impact on policy making, wherever modeling and simulation is used ? in science, logistics, social behavioral, transportation management, health, and land to mention only some examples.