DAP Capabilities
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Revision as of 19:57, 5 March 2010 by Ndp (talk | contribs) (→How might a DAP Capabilities response look)
Overview
Develop a definition of what a DAP servers Capabilities response should ;ook like.
What is a Capabilities response?
In the world of OGC it's a document that contains a description of the ownership (ows:ServiceProvider), service identification (ows:ServiceIdentification), service access (ows:OperationsMetadata), and holdings (*:Contents) of the server.
What are we doing now that's similar?
- Ownership Nothing similar. Data providers can (but none that I have seen have) configure the OLFS to replace the standard documentation found through the Documentation link on every contents.html page. Otherwise they might get an email address about weho to write of the BES sends one in an error. The OLFS saves propagates the email address support@opendap.org from 14 different places in the code through a number of HTML responses . These could be modified by determined Hyrax installer, but it would be a hassle and wouldn't persist between installs. We have no structured response in this regard.
- Service Identification Nothing similar. In the current version of Hyrax we return an list of the DAP versions the server supports in a larger XML document containing the names and version numbers of the software components running on the server.
- Service Access Nothing similar
- Holdings Currently we provide a linked list of holdings through THREDDS catalogs. Our THREDDS catalogs do not contain any THREDDS metadata, (or WCS metadata for that matter)
How might a DAP Capabilities response look
Ownership
<dap:Contact> <dap:Email>name@org.org</dap:Email> <dap:/Contact>
Holdings
<dap:CatalogRoot xlink:href="/opendap/catalog.xml" >
Services
<dap:Services> <dap:ServiceIdentification name="hyrax" base="/opendap/hyrax/" > <dap:ServiceType>DAP</dap:ServiceType> <dap:Version>2.0</dap:Version> <dap:Version>3.1</dap:Version> <dap:Version>3.2</dap:Version> <dap:CatalogRoot xlink:href="/opendap/catalog.xml" > <dap:ReturnFormat>DAP</dap:ReturnFormat> <dap:ReturnFormat>NetCDF</dap:ReturnFormat> <dap:ServiceIdentification> <dap:ServiceIdentification name="hyrax-WCS" base="/opendap/WCS/" > <dap:ServiceType>WCS</dap:ServiceType> <dap:Version>1.1.2</dap:Version> <dap:CatalogRoot xlink:href="/opendap/WCS?service=WCS&version=1.1.2&request=GetCapabilities" > <dap:ServiceIdentification> </dap:Services>
Server-side functions.
We need to develop XML machine readable description of server side functions. Here's a straw man for geogrid, grid, linear_scale, and version:
<dap:ServerSideFunctions> <dap:ServerSideFunction> <dap:Name>geogrid</dap:Name> <dap:Description> The geogrid() function applies a constraint given in latitude and longitude to a DAP Grid variable. The arguments to the function are: geogrid(variable, top, left, bottom, right[, expression ...]) The variable is the data to be sub-sampled. The Top, left, bottom, right are the latitude and longitude coordinates of the northwesterm and southeastern corners of the selection box. The expressions consist of one or more quoted relational expressions. Each relational expression is applied to the grid using the server's constraint evaluator and the resulting grid is returned. The expressions may use constants and the grid's map vectors but may not use any other variables. In particular, you cannot use the grid values themselves. Two forms of expression are provided: "var relop const" and "const relop var relop const" Where relop stands for one of the relational operators, like = and > For example: grid(sst,"20>TIME>=10") and grid(sst,"20>TIME","TIME>=10") are both legal and, in this case, also equivalent. </dap:Description> <dap:Parameter occurrence="1" presence="required" > <dap:Name>variable</dap:Name> <dap:Type>String</dap:Type> <dap:Description>The name of the Grid variable to subsample.</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>top</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>Latitude Coordinate</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>left</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>Longitude Coordinate</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>bottom</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>Latitude Coordinate</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>right</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>Longitude Coordinate</dap:Description> </Parameter> <dap:Parameter occurrence="*" presence="optional" > <dap:Name>expression</dap:Name> <dap:Type>String</dap:Type> <dap:Description>A Relational Expression</dap:Description> </Parameter> </dap:ServerSideFunction> <dap:ServerSideFunction> <dap:Name>grid</dap:Name> <dap:Description> The grid() function takes a DAP Grid variable and zero or more relational expressions. Each relational expression is applied to the grid using the server's constraint evaluator and the resulting grid is returned. The expressions may use constants and the grid's map vectors but may not use any other variables. In particular, you cannot use the grid values themselves. Two forms of expression are provided: "var relop const" and "const relop var relop const" Where relop stands for one of the relational operators, like = and > For example: grid(sst,"20>TIME>=10") and grid(sst,"20>TIME","TIME>=10") are both legal and, in this case, also equivalent. </dap:Description> <dap:Parameter occurrence="1" presence="required" > <dap:Name>variable</dap:Name> <dap:Type>String</dap:Type> <dap:Description>The name of the Grid variable to subsample.</dap:Description> </Parameter> <dap:Parameter occurrence="*" presence="required" > <dap:Name>expression</dap:Name> <dap:Type>String</dap:Type> <dap:Description>A Relational Expression</dap:Description> </Parameter> </dap:ServerSideFunction> <dap:ServerSideFunction> <dap:Name>linear_scale</dap:Name> <dap:Description> The linear_scale() function applies the familiar y = mx + b equation to data. It has three forms: linear_scale(var), linear_scale(var,scale_factor,add_offset) linear_scale(var,scale_factor,add_offset,missing_value) If only the name of a variable is given, the function looks for the COARDS/CF-1.0 scale_factor, add_offset and missing_value attributes. In the equation, 'm' is scale_factor, 'b' is add_offset and data values that match missing_value are not scaled. If add_offset cannot be found, it defaults to zero; if missing_value cannot be found, the test for it is not performed. In the second and third form, if the given values conflict with the dataset's attributes, the given values override. </dap:Description> <dap:Parameter occurrence="1" presence="required" > <dap:Name>var</dap:Name> <dap:Type>String</dap:Type> <dap:Description>The name of the Grid variable to subsample.</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>scale_factor</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>The "m" in "y = mx + b"</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>add_offset</dap:Name> <dap:Type>String</dap:Type> <dap:Description>The "b" in "y = mx + b"</dap:Description> </Parameter> <dap:Parameter occurrence="1" presence="required" > <dap:Name>missing_value</dap:Name> <dap:Type>Float</dap:Type> <dap:Description>A data values that match missing_value are not scaled.</dap:Description> </Parameter> </dap:ServerSideFunction> <dap:ServerSideFunction> <dap:Name>version</dap:Name> <dap:Description> The version function provides a list of the server-side processing functions available on a given server along with their versions. For information on a specific function, call it with no arguments or look at this page. </dap:Description> </dap:ServerSideFunction> </dap:ServerSideFunctions>