基于网格的分布式虚拟环境仿真海量数据管理

分析了分布式虚拟环境仿真的特点,提出了基于网格的分布式虚拟环境仿真的海量数据管理框架.该框架结构采用分层结构,自底向上依次为网格节点、高性能通信系统、数据存储与处理系统和计算系统.给出了一个基于上述体系结构的原型系统.对该原型系统的仿真结果表明,该海量数据管理体系结构设计符合虚拟环境仿真实时性、稳定性和高可靠性的要求.     

A GIS-based urban simulation model for environmental health analysis

This paper introduces an urban simulation model for environmental health analysis (SIENA). SIENA is a novel tool to explore urban interactions and processes with regard to exposure assessments. It is based on urban structures and relationships observed in real-world cities making it a realistic representation of a functioning city. The development of SIENA involved identifying and quantifying fundamental processes and similarities in urban areas in Great Britain and using those to guide the building of SIENA within a GIS. An internal validation confirmed SIENA's realism. Its generality, achieved through the pooling of information from different real-world cities, makes it particularly useful for developing and testing spatial epidemiological concepts and models; simulating processes and interactions relating to environmental exposure; and exploring theoretical and methodological problems in the spatial analysis of environmental health. SIENA ultimately provides a much needed tool in the form of a controlled, simplified urban simulation model.     

异构数据源城市道路仿真模型接口

根据编译原理中的自动机理论,给出了异构数据源城市道路仿真模型的接口设计及接口实现算法,数据交换采用中性文件交换方式。以DXF格式源文件为例,建立图形实体自动机模型,通过状态转换图跟踪读取信息的轨迹;并给出了城市道路仿真模型在目标平台上重生成时的UML类图。结果表明,自动机理论为交通系统仿真建模提供了一条新的思路和方法,同时使异构数据源城市道路仿真模型接口实现具有一定的理论依据,有利于城市道路基础数据源的共享和重用。     

Multi-level association rules and directed graphs for spatial data analysis

We propose a methodology that upgrades the methods of the Lagrangian analysis of surface sea-water parcels. This methodology includes data mining with efficient visualization techniques, namely, spatial–temporal association rules and multi-level directed graphs with different levels of space and time granularity. In the resulting multi-level directed graphs we can intertwine knowledge from various disciplines related to oceanography (in our application) and perform the mining of such graphs. We evaluate the proposed methodology on Lagrangian tracking of virtual particles in the velocity field of the numerical model called the Mediterranean Ocean Forecasting Model (MFS). We describe an efficient algorithm based on label propagation clustering, which finds cycles and paths in multi-level directed graphs and reveals how the number and size of the cycles depend on the seasons. In addition, we offer three interesting results of the visualization and mining of such graphs, that is, the 12 months periodicity of the exchange of water masses among sea areas, the separation of Mediterranean Sea circulation in summer and winter situations, obtained with the hierarchical clustering of multi-level directed graphs, and finally, with visualization with multi-level directed graphs we confirm the reversal of sea circulation in the Ionian Sea over the last decades. The aforementioned results received a very favorable evaluation from oceanographic experts.     

P2P环境中的空间数据索引模型和生成算法研究

在Peer-to-Peer（P2P）环境中管理复杂的空间数据,首先需要建立空间数据索引。对相关研究进行了分析总结,设计出了一种分布式四叉树与本地R*树相结合的新索引模型P2PQR-tree。P2PQR-tree将四叉树技术应用于P2P环境,并利用复制策略实现了负载均衡。给出了索引生成算法,并对算法性能进行了分析。P2PQR-tree数据组织更加合理、能够更好地支持元数据管理、易于实现权限控制、减少了分布式索引变化,更好地适应了对等网络的动态特性。     

A practical approach to data modelling in spatial applications

The storage and manipulation of spatial data requires a different style of support from that normally found in commercial database systems. This paper explores the use of the functional data model and the high level language Daplex to provide an integrated tool for the conceptual modelling of spatial data and the manipulation of data values. Importance is attached to allowing dynamic schema definition and to the provision of abstract data types to support spatial objects. The implementation comprises three separate modules and uses an underlying relational DBMS to store all metadata and data values. This modular design has enabled the user interface, Daplex language and storage aspects of the software to be developed independently, creating a system which has already proved to be easily portable. Consideration has also been given to ways of improving system performance.     

Planning optimal paths: A simple assessment of survey spatial knowledge in virtual environments

In spatial cognition studies several cognitive factors were analysed in order to identify the aspect that could constitute the basis for the capacity of organising spatial knowledge into survey maps.     

Higher-order co-occurrences for exploratory point pattern analysis and decision tree clustering on spatial data

Analyzing geographical patterns by collocating events, objects or their attributes has a long history in surveillance and monitoring, and is particularly applied in environmental contexts, such as ecology or epidemiology. The identification of patterns or structures at some scales can be addressed using spatial statistics, particularly marked point processes methodologies. Classification and regression trees are also related to this goal of finding “patterns” by deducing the hierarchy of influence of variables on a dependent outcome. Such variable selection methods have been applied to spatial data, but, often without explicitly acknowledging the spatial dependence. Many methods routinely used in exploratory point pattern analysis are2nd-order statistics, used in a univariate context, though there is also a wide literature on modelling methods for multivariate point pattern processes. This paper proposes an exploratory approach for multivariate spatial data using higher-order statistics built from co-occurrences of events or marks given by the point processes. A spatial entropy measure, derived from these multinomial distributions of co-occurrences at a given order, constitutes the basis of the proposed exploratory methods.     

A data management scheme for effective walkthrough in large-scale virtual environments

As the complexity of virtual environments increases, it becomes a critical issue to maintain the quality of a walkthrough experience. In this paper, we propose an effective data management scheme to address this issue in client-server architecture. First, we propose using real-time scene management to manage the computing resources on the client side by reducing the amount of transmitted geometry data. Second, we propose a prioritized most likelihood movement model to prefetch potential future objects based on the users current motion intention. Lastly, a hybrid coherence cache model is proposed to take advantages of both the temporal and spatial localities of the walkthrough process. We have done extensive experiments to demonstrate how these techniques can improve the effectiveness of walkthrough in a large virtual environment.     

A spatial model for complex objects with a broad boundary supporting queries on uncertain data

This paper proposes a new data model for spatial databases that supports spatial entities with a broad boundary. The model is proposed as a solution to the problem of handling uncertainty in spatial data. Broad boundaries absorb all the uncertainty by which spatial data are commonly affected and allow computations in presence of uncertainty without rough simplifications of the reality. A specific model for topological relations between regions with a broad boundary is then developed and hierarchically structured topological operators are proposed. Such operators allow users to progressively refine their queries and constitute the basis for a spatial extension to SQL. The model proposed in the paper can be easily integrated into existing data models for spatial databases.     

Quantitative analysis of a certified e-mail protocol in mobile environments: A probabilistic model checking approach

Formal analysis techniques, such as probabilistic model checking, offer an effective mechanism for model-based performance and verification studies of communication systems’ behavior that can be abstractly described by a set of rules i.e., a protocol. This article presents an integrated approach for the quantitative analysis of the Certified E-mail Message Delivery (CEMD) protocol that provides security properties to electronic mail services. The proposed scheme employs a probabilistic model checking analysis and provides for the first time insights on the impact of CEMD’s error tolerance on computational and transmission cost. It exploits an efficient combination of quantitative analysis and specific computational and communication parameters, i.e., the widely used Texas Instruments TMS320C55x Family operating in an High Speed Downlink Packet Access (HSDPA) mobile environment, where multiple CEMD participants execute parallel sessions with high bit error rates (BERs). Furthermore, it offers a tool-assistant approach for the protocol designers and analysts towards the verification of their products under varying parameters. Finally, this analysis can be also utilized towards reliably addressing cost-related issues of certain communication protocols and deciding on their cost-dependent viability, taking into account limitations that are introduced by hardware specifications of mobile devices and noisy mobile environments.     

矢量空间数据库中关联规则的挖掘算法研究

按照矢量空间数据的特点和空间数据挖掘的要求,以GIS的空间分析和空间数据处理为工具,探讨了矢量空间数据库中关联规则挖掘的数据处理方法,提出了关联规则的挖掘算法。最后,通过实例进行了验证。     

Collaborative distributed environments for learning design tasks by means of modelling and simulation

The Simulation discipline has to face new challenges such as the incorporation of Collaborative Technologies for professional use as well as for teaching purposes. This integration permits the creation of new kinds of support for collaborative learning processes. In this paper, we explore the potential of this synergy with DomoSim-TPC, a synchronous distributed collaborative environment for the teaching and learning of Domotics. The system supports an active, simulation-based and problem-based approach for learning house automation design. Using this learning environment, teachers propose and organize problem solving activities and the students carry out, in a collaborative way, the construction of artefacts (designs) using modelling and simulation tools.     

关系数据模型与面向对象数据模型的关系探讨

面向对象数据模型的应用打破了油田单一关系数据库体系架构。如何在面向对象数据模型和关系数据模型并存条件下构建和优化协调统一的数据库体系架构,是油田数据库建设的重要技术方向之一。本文从油田数据库应用的角度概要对比了关系数据模型和面向对象数据模型的特点,对关系数据模型和面向对象数据模型共存条件下建立油田数据库体系架构的可能性进行了探讨。     

新的空间数据模型选取方法与实现

空间数据模型是地理信息系统开发应用的核心和基础,选择合适的空间数据模型,直接关系到整个系统的算法实现和开发效率.结合软件工程学的思想,提出一种新的空间数据模型选取方法,并以城镇土地定级估价系统的构建为例,详细介绍该方法的实现过程.实践表明,该方法具有抗风险、敏捷等特点,在实际工程运用中具有较好的可行性和优越性.     

A gamified peer assessment model for on-line learning environments in a competitive context

Peer Assessment (PA) offers a powerful solution that helps teachers in online learning environments to correct essays by distributing the workload among students. Nevertheless, the quality of the results in PA depends on good evaluations of reviewers. Thus, the main drawback for scaling up the use of PA is the presence of inadequate behaviours, such as being too harsh or too soft in the assessment, or even not offering a helpful feedback. This usually occurs due to the lack of motivation and engagement of students in the PA process. To deal with this problem, this paper proposes a gamified peer assessment model, where gamification elements are used to engage students in PA activities. Two experiments using the proposed model within an intelligent tutoring system called MeuTutor shows satisfactory outcomes. We verified that the average grade given by students to an essay are equivalent to those given by experts, but the time and costs to complete the assessments were largely reduced. Furthermore, the use of gamification helped to increase the amount of students' access to the system in 64.28%; increase in 10.53% the number of essays written and submitted; and improve the quantity and quality of assessments for each essay.     

Collaborative virtual geographic environments: A case study of air pollution simulation

The integration of high dimensional geo-visualization, geo-data management, geo-process modeling and computation, geospatial analysis, and geo-collaboration is a trend in GIScience. The technical platform that matches the trend forms a new framework unlike that of GIS and is conceptualized in this paper as a collaborative virtual geographic environment (CVGE). This paper focuses on two key issues. One is scientific research on CVGE including the concept definition and the conceptual and system framework development. The other is a prototype system development according to CVGE frameworks for air pollution simulation in the Pearl River Delta. The prototype system integrates air pollution source data, air pollution dispersion models, air pollution distribution/dispersion visualization in geographically referenced environments, geospatial analysis, and geo-collaboration. Using the prototype system, participants from geographically distributed locations can join in the shared virtual geographic environment to conduct collaborative simulation of air pollution dispersion. The collaborations supporting this simulation happen on air pollution source editing, air pollution dispersion modeling, geo-visualization of the output of the modeling, and geo-analysis.