基于元数据和CORBA服务的地图数据网络分发系统

利用空间地图数据（SMD）的海量特征、多尺度、广泛性和其离散分布适合于网络环境分布、共享、异构和可扩展的应用特点，提出了SMD远程分发的地图数据网络分发（MDND）系统．首先定义了SMD、元数据和以图论的方式描述的网络资源节点，建立了SMD资源与网络资源的关系，然后给出了MDND的形式化定义和基于CORBA的SMD分发架构及其系列分布服务，创建了基于元数据的查询条件输入方法，并在元数据集查询服务和地理信息路由指向服务的基础上实现了MDND．经CORBA服务、FTP和直接拷贝等模式的性能比较表明，所提系统可以有效完成SMD分发，在CORBA服务模式下的传输性能与直接拷贝模式相当却明显优于FTP模式，能快速达到最大传输速率且对数据量的依赖性不强．

Map Data Network Dissemination System Based on Metadata and CORBA Services

Taking advantage of some characteristics of spatial map data(SMD),such as mass data,multi-scales,universality,and discrete distribution that is suitable to be processed in the network environment with distributive,sharing,self-adaptive,heterogeneous and scalable features,a map data network dissemination(MDND)system for disseminating SMD to remote users is presented.!Firstly,SMD,the associated metadata and the network resource nodes described as a graphic form are defined.The relations between SMD and network resources are established.After giving formulized definition to MDND,SMD dissemination framework and series of services based on CORBA, the input methods are provided according to the three query conditions of metadata.MDND is implemented on the basis of metadata set inquiry service and route-pointed service of geographic information.Comparision in the modes of CORBA service,FTP and direct copy shows that the proposed system can effectively achieve SMD dissemination,its transfer performance in CORBA service mode is equivalent to the direct copy,better than FTP,and it approaches to the biggest transfer rate more quickly with weak dependence on data amount.