This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
>To: address@hidden >cc: address@hidden >From: Zhangfan Xing <address@hidden> >Subject: virtual data >Organization: UCAR/Unidata >Keywords: 200204252155.g3PLtja18355 Hi Zhangfan, > I would like to know if the current netcdf lib > supports virtual data, i.e., a netcdf entry file > serves data spanning multiple physical files. > It's been mentioned in your FAQ as future plan. > Has that ever got implemented? No, not directly. However as part of the DODS (distributed Oceanographic Data System) project, we have implemented an "aggregation server" which makes multiple netCDF files look like one larger netCDF dataset to its clients. The aggregation server is currently in beta testing. The configuration files are expected to change somewhat, and a 1.0 release will be made by the end of May, 2002. See http://www.unidata.ucar.edu/projects/THREDDS/tech/DODSAggServer.html for more information. As explained on that page, it currently supports three kinds of aggregation. There were always some semantic problems with the original idea of virtual data that were troublesome. For example, how could a dimension be shared between two variables in different datasets? If the size of the dimension changed in one of the datasets so that they were no longer consistent, what should an inquiry of the dimension size return? The aggregation server approach is letting us explore what kinds of aggregations are meaningful and useful and what constraints are required to avoid such problems. --Russ _____________________________________________________________________ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu