DAP Capabilities

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Revision as of 19:36, 5 March 2010 by Ndp (talk | contribs) (Server-side functions.)

1 Overview

Develop a definition of what a DAP servers Capabilities response should ;ook like.

2 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.

3 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)

4 How might a DAP Capabilities response look

4.1 Ownership


4.2 Server-side functions.

We need to develop XML machine readable description of server side functions. Here's a straw man:

           <dap:Parameter occurrence="1" presence="required" >
               <dap:Description>The name of the Grid variable to subsample.</dap:Description>
           <dap:Parameter occurrence="1" presence="required" >
               <dap:Description>Latitude Coordinate</dap:Description>
           <dap:Parameter occurrence="1" presence="required" >
               <dap:Description>Longitude Coordinate</dap:Description>
           <dap:Parameter occurrence="1" presence="required" >
               <dap:Description>Latitude Coordinate</dap:Description>
           <dap:Parameter occurrence="1" presence="required" >
               <dap:Description>Longitude Coordinate</dap:Description>
           <dap:Parameter occurrence="*" presence="optional" >
               <dap:Description>A Relational Expression</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.

4.3 Holdings

         <dap:CatalogRoot xlink:href="/opendap/catalog.xml" >

4.4 Services

       <dap:ServiceIdentification name="hyrax" base="/opendap/hyrax/" >
         <dap:CatalogRoot xlink:href="/opendap/catalog.xml" >
       <dap:ServiceIdentification name="hyrax-WCS" base="/opendap/WCS/" >
         <dap:CatalogRoot xlink:href="/opendap/WCS?service=WCS&version=1.1.2&request=GetCapabilities" >