Free Choice Systems Research Articles

Tackling school segregation with transportation network interventions: an agent-based modelling approach

We address the emerging challenge of school segregation within the context of free school choice systems. Households take into account both proximity and demographic composition when deciding on which schools to send their children to, potentially exacerbating residential segregation. This raises an important question: can we strategically intervene in transportation networks to enhance school access and mitigate segregation? In this paper, we propose a novel, network agent-based model to explore this question. Through simulations in both synthetic and real-world networks, we demonstrate that enhancing school accessibility via transportation network interventions can lead to a reduction in school segregation, under specific conditions. We introduce group-based network centrality measures and show that increasing the centrality of certain neighborhood nodes with respect to a transportation network can be an effective strategy for strategic interventions. We conduct experiments in two synthetic network environments, as well as in an environment based on real-world data from Amsterdam, the Netherlands. In both cases, we simulate a population of representative agents emulating real citizens’ schooling preferences, and we assume that agents belong to two different groups (e.g., based on migration background). We show that, under specific homophily regimes in the population, school segregation can be reduced by up to 35%. Our proposed framework provides the foundation to explore how citizens’ preferences, school capacity, and public transportation can shape patterns of urban segregation.

Analysis and Transformation of Overlapped Patterns in BPEL Process Modeling

PDF HTML阅读 XML下载 导出引用 引用提醒 BPEL 流程建模中的交叠模式分析与转换 DOI: 10.3724/SP.J.1001.2011.04075 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(60910004, 60873018, 91018010, 61003078, 61003079, 61133001); 国家重点基础研究发展计划(973)(2010CB328102); 国家教育部博士点基金(200807010012); 中央高校基本科研业务费专项资金(JY10000903004); 综合业务网国家重点实验室基金(201102001) Analysis and Transformation of Overlapped Patterns in BPEL Process Modeling Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:由图形化流程建模语言生成可执行的业务流程语言(business process execution language,简称BPEL)时,对于源模型中顺序与并发结构交织的情况(称为交叠模式),传统的复制相关活动方法缺少系统分析及形式化描述.针对这一现状,提出基于工作流网的UML 活动图生成BPEL 方法,以自由选择工作流网作为活动图的理论基础,利用活的、有界的自由选择网系统的合成规则,定义合理的自由选择工作流网中的两种交叠模式,针对其中一种给出复制相关活动的形式化转换方法,并借助Petri 网的并发正则表达式证明转换等价性,说明另一种交叠模式中复制相关活动方法的适用范围.针对BPEL 流程建模及图形化流程语言生成块状语言过程中的交叠模式转换问题,给出形式化的描述与解决方法. Abstract:During the derivation of the business process execution language (BPEL) from graph-oriented process modeling languages, there exist structures called overlapped patterns, which mix sequential and parallel structures together. The existing duplication approach lacks systematical analysis and formal presentations. In view of this problem, a transformation of UML activity diagrams to BPEL based on WF-nets is proposed. By choosing free choice WF-nets as the foundation of activity diagrams and by utilizing the synthesis rules of live and bounded free choice systems, two types of overlapped patterns are defined. For one type of patter, the duplication method is formally represented, and the transformation equivalence is proved using the concurrent regular expressions of Petri nets. For the other type, the applicable range of the duplication method is described. This method presents a solution in formal representations to the transformation of overlapped patterns in BPEL modeling, and distinguishes the derivation of the block-oriented modeling languages from graph-oriented ones. 参考文献 相似文献 引证文献

Free-Choice Petri Nets without Frozen Tokens, and Bipolar Synchronization Systems

Bipolar synchronization systems (BP-systems) constitute a class of coloured Petri nets, well suited for modelling the control flow of discrete dynamical systems. Every BP-system has an underlying ordinary Petri net, a T-system. It further has a second ordinary net attached, a free-choice system. We prove that a BP-system is safe and live if the T-system and the free-choice system are safe and live and the free-choice system in addition has no frozen tokens. This result is the converse of a theorem of Genrich and Thiagarajan and proves an old conjecture. As a consequence we obtain two results about the existence of safe and live BP-systems with prescribed ordinary Petri nets. For the proof of these theorems we introduce the concept of a morphism between Petri nets as a means of comparing different Petri nets. We then apply the classical theory of free-choice systems.

Structure theory of equal conflict systems

Equal conflict net systems are a weighted generalisation of the (extended) free choice subclass that keeps the total autonomy of choices. A substantial part of the analytical branch of the structure theory of free choice systems, including decomposition and duality, the rank theorem, characterisations of impartial sequences and prompt interfaces, and the existence of home states, is extended to the equal conflict case. In so doing, several familiar concepts and objects from the structure theory of place/transition net systems are revisited from a linear algebraic perspective, which is specially adequate to cope with weighted nets.

Reachability in cyclic extended free-choice systems

The reachability problem for Petri nets can be stated as follows: Given a Petri net ( N, M 0) and a marking M of N, does M belong to the state space of ( N, M 0)? We give a structural characterisation of reachable states for a subclass of extended free-choice Petri nets. The nets of this subclass are those enjoying three properties of good behaviour: liveness, boundedness and cyclicity. We show that the reachability relation can be computed from the information provided by the S-invariants and the traps of the net. This leads to a polynomial algorithm to decide if a marking is reachable.

Traps characterize home states in free choice systems

Free choice nets are a subclass of Petri nets allowing to model concurrency and nondeterministic choice, but with the restriction that choices cannot be influenced externally. Home states are ground markings which can be reached from any other reachable marking of a system. A trap is a structurally defined part of a net with the property that once it is marked (that is, carries at least one token), it will remain remarked in any successor marking. The main result of this paper characterizes the home states of a live and bounded free choice system by the property that all traps are marked. This characterization leads to a polynomial-time algorithm for deciding the home state property. Other consequences include the proof that executing all parts of a net at least once necessarily leads to a home state; this has been a long standing conjecture.

Free choice systems have home states

This paper contains a proof that live and safe free choice Petri nets have home states. Home states are ones which can be reached from every successor state of the initial state. Liveness means that all actions remain executable, and safeness means that all capacities are finite. The result is interesting because it may help in the analysis of behavioural properties of complex systems. The existence of home states is a strong property which (as we will also show) fails to hold for a slightly generalised class of nets.

A multiple free choice model for pigs

Multiple free choice systems may provide one way of evaluating the relative preference of animals for different housing systems. This paper proposes a possible model that attempts to take into consideration previous criticism on multiple free choice systems. A hexagonal housing system was constructed with 6 identical cubicles, which allowed elimination of all variables except the one to be investigated. Barriers could be introduced at the entrance to each cubicle to prevent easy access to the cubicle of preference. To test the usefulness of this system, several different types of flooring were used. In each cubicle, we introduced either sawdust, straw, concrete, concrete slats, perforated metal, rubber or plywood. The results clearly indicate that preferences for a particular type of flooring may be investigated by this model.