求教：在gis9.1中，network analyst和utility network analyst两个模块的异同？请各位朋友帮忙解答。

<P><img src="images/post/smile/dvbbs/em02.gif" /> 在arcgis9.1中又新增了一个扩展模块network analyst，这个也是可以进行gis的网络分析的，但是不知道network analyst和utility network analyst两个模块的有什么不同之处，和相同之处？它们之间有什么联系？请各位朋友帮忙讨论解答，非常感谢。</P>

<P>From the GIS Dictionary ( <a href="http://support.esri.com/index.cfm?fa=knowledgebase.gisDictionary.gateway" target="_blank" >http://support.esri.com/index.cfm?fa=knowledgebase.gisDictionary.gateway</A> ): <BR>- A NETWORK DATASET is a collection of topologically connected network elements (edges, junctions and turns) that are derived from network sources, typically used to represent a linear network, such as a road or subway system. Each network element is associated with a collection of network attributes. Network datasets are typically used to model undirected flow systems. <BR>- A GEOMETRIC NETWORK is a collection of topologically connected edge and junction features that represent a linear network such as a utility or hydrologic system. The connectivity of features within a geometric network is based on their geometric coincidence. A geometric network does not contain information about the connectivity of features; this information is stored within a logical network. Geometric networks are typically used to model directed flow systems. <BR>- A LOGICAL NETWORK is an abstract representation of a network, consisting of a collection of hidden tables. A logical network contains edge, junction, and turn elements or features, the connectivity between them, and the weights necessary for traversing the network. It does not contain information about the geometry or location of its elements or features; this information is one of the components of a network system. </P>
<P>The geometric network and the network dataset are two different entities in the geodatabase. Both the geometric network and the network dataset have an associated logical network to store network connectivity and attributes/weights for use when performing network analysis. One of the major differences between the geometric network and the network dataset is how each of them maintains its logical network. As you noted in <a href="http://edndoc.esri.com/arcobjects/9.1/ArcGISDevHelp/TechnicalDocuments/Network/ArcGISNetworkModel/ArcGISNetwork.htm" target="_blank" >http://edndoc.esri.com/arcobjects/9.1/ArcGISDevHelp/TechnicalDocuments/Network/ArcGISNetworkModel/ArcGISNetwork.htm</A> the geometric network automatically updates its logical network immediately after an edit is made. The network dataset, on the other hand, does not automatically update its logical network. It updates it when the network is rebuilt ( as noted in <a href="http://webhelp.esri.com/arcgisdesktop/9.1/index.cfm?ID=2603;TopicName=Editing%20network%20datasets;rand=541;pid=2597" target="_blank" >http://webhelp.esri.com/arcgisdesktop/9.1/index.cfm?ID=2603;TopicName=Editing%20network%20datasets;rand=541;pid=2597</A> ). </P>

太复杂