OPeNDAP/THREDDS Directory Views

[Christopher Lynnes]

My vote is anything BUT Option 1.

I like the OPeNDAP presentation view the best, in that access to the  
various responses is available directly from the list.

As for problems (2) and (3), problem #2 could be viewed by some sites  
as a feature.  That is, datasets can be presented within the OPeNDAP  
view but not within the THREDDS view.  This could be useful for  
testing, performance considerations, custom THREDDS catalogs, etc.

On Apr 12, 2007, at 5:52 PM, Nathan Potter wrote:

>
> Greetings,
>
> I would like to get some feedback about one of the OPeNDAP  
> "services" and some possible changes to (or elimination/replacement  
> of) the service.
>
> OPeNDAP Directory/Contents
>
> OPeNDAP servers offer a "presentation view" of each collection of  
> datasets on the server. Typically this has been accessed by using a  
> browser to open a URL ending in "/". The OPeNDAP sever returns an  
> HTML document that the browser renders in human readable form.  In  
> server 3 this view was generated by the Apache web server.
>
> Server 3 example: http://test.opendap.org/opendap-3.7/nph-dods/data/ 
> nc/
>
> With Hyrax we have integrated THREDDS catalogs into our server.  
> THREDDS has it's own presentation view which is different from the  
> OPeNDAP presentation view.
>
> Hyrax OPeNDAP presentation view: http://test.opendap.org:8080/ 
> opendap/data/nc/contents.html
> Hyrax THREDDS presentation view: http://test.opendap.org:8080/ 
> opendap/data/nc/catalog.html
>
>
> Unfortunately this is already creating problems:
>
> 1) The THREDDS view may contain additional datasets that are not  
> visible in the OPeNDAP view. (Data providers may add datasets to  
> the catalog that are not associated with data served by the BES)
>
> 2) If the THREDDS catalog.xml doesn't contain a datasetScan element  
> for each of the datasets/directories at the top level of the server  
> then the omitted ones will not appear in the THREDDS view (and  
> catalog). This means that the OPeNDAP view may include datasets  
> that the THREDDS view does not.
>
> 3) The OPeNDAP view differentiates between files that the server  
> recognizes as data and ones it does not. The dataset links in the  
> OPeNDAP view lead to the HTML data request form for data, and will  
> simply return the contents of the file if the server doesn't  
> recognize it as a dataset that it can handle. The THREDDS view is  
> built using the assumption that everything returned in a  
> datasetScan is data. So - THREDDS views don't really have a way to  
> include README files - they show up as a dataset and drilling down  
> leads to broken links and not to access to the file.
>
>
> - I can fix (1).
>
> - Fixing (2) is really a configuration problem that has to be  
> solved by each data provider.
>
> - Fixing (3) is much harder, and begs the question: Why support 2  
> views at all?
>
>
>
> ** OPTION 1 **
> Drop the OPeNDAP presentation view. If we can live with just the  
> THREDDS view then I don't need to fix (1). Problem (2) will be  
> addressed more readily by data providers because the THREDDS  
> catalog will need to be correctly configured for the server to  
> produce THREDDS catalogs and views. The draw back to this is that  
> we would loose the ability to serve "flat files" - README,  
> index.html, info.html, images, etc.
>
>
> ** OPTION 2 **
> Fix (1) and live with (2) and (3), broken links and all.
>
>
> ** OPTION 3 **
> Work with the THREDDS group and woo them to the idea that (3) is a  
> problem and that the THREDDS API's (and catalogs?) need to modified  
> to solve (3). I suspect we could do it by adding a different  
> "service" for the flat files. The CrawlableDataset interface would  
> have to modified so that it could be used to identify which files  
> were to be served using which service. When the datasetScan  
> elements are accessed the catalog get built with the serviceName  
> pointing to the OPeNDAP service for data, to the file service for  
> files that are not data... But I am speculating as I haven't spoken  
> our esteemed THREDDS colleagues.
>
>
>
> What do people think?
>
> Is OPTION 1 viable?
>
> Other ideas/options/thoughts/opinions?
>
>
> Nathan
>
>
>
>
> = 
> Nathan Potter                        ndp at opendap.org
> OPeNDAP, Inc.                        541.752.1852
>

--
Christopher Lynnes             NASA/GSFC, Code 610.2          
301-614-5185