including XML, JSON, HTML and ASCII. In response to requests for content, OPeNDAP servers can respond with multi-part mime documents that include a binary portion with NetCDF or DAP-native encoding. (These binary forms offer compact means to deliver large volumes of content, and the DAP-native form may even be streamed if desired.) OPeNDAP's software for building DAP servers (on top of Apache) is dubbed Hyrax and includes adapters that facilitate serving a wide variety of source data. DAP servers most frequently enable (remote) access to (large) HDF or NetCDF files, but the source data can exist in databases or other formats, including user-defined ones. When source data are organized as files, DAP retrievals enable, via subsetting, finer-grained access than does the FTP. Furthermore, OPeNDAP servers can aggregate subsets from multiple files for delivery in a single retrieval. Taken together, subsetting, aggregation and streaming can yield substantial data-access efficiencies, even in the presence of slow networks. OPeNDAP and other DAP servers are used operationally in government agencies, including NASA and NOAA, for providing access to Earth science data, including satellite imagery and other high-volume information sources. The DAP data model embraces a comprehensive set of data structures, including multidimensional arrays and nested sequences (i.e., records), complemented by a correspondingly rich set of constraint expressions. Hence the OPeNDAP data-retrieval architecture has demonstrated utility across a broad range of scientific data types, including data generated via simulations and data generated via observations (whether remotely sensed or measured in situ). References External links OPeNDAP.org Tutorial on using OPeNDAP for data access at PO.DAAC (NASA's Distributed Active Archive Center for Physical Oceanography) THREDDS -- Thematic Realtime Environmental Distributed Data Services dapper - OPeNDAP server for in-situ data DChart - Web viewer for NOAA Observing System data (in-situ data) GrADS ncBrowse - Java viewer for OPeNDAP netCDF files (supports wide range of netCDF conventions) netCDF Explorer - netCDF Explorer is multi-platform graphical browser for netCDF files. netCDF Explorer can browse files locally or remotely, by means of OPeNDAP NCAR Command Language - analysis and visualization software Ferret Pydap - client/server implementation written in Python ERDDAP - OPeNDAP server for gridded and tabular data; supports a wide range of output file formats NASA GCMD OPeNDAP portal Global Change Master Directory (GCMD) Asia-Pacific Data Research Center -- a textbook example OPenDAP implementation Earth sciences Web services Data analysis Technical communication Meteorological data and networks Earth sciences data formats