Basic usage of LINK for VOTable in Aladin

Pierre Fernique Pierre.Fernique at
Thu May 31 19:25:10 CEST 2018

Hi DAL, Apps members,

For VOTable providers which want to see usable links in Aladin here the 
basic recipe (see example below).

Just add *<LINK* in your *<FIELD* which are describing your URLs column. 
This method is described in the normative part of VOTable document. By 
this way you will be able to describe the "title of the link" and the 
"content-type" of the result (the URLs are in the cells of the table)

This simple LINK description in the FIELD will allows Aladin to decide 
how to display your link, the title which will appear in the table cells 
(instead of the full URL), and the action to do :

  * basic link to open a web browser,
  * button to load your result in the Aladin itself (if the content-type
    describes a datatype consumable by Aladin (image, catalog, MOC, HiPS)),
  * button to send the result to an aware SAMP client for non supported
    data type (spectrum for instance),
  * popup menu for a datalink stream
  * ...

Example: A link which returns Datalink results

       <FIELD name="access_url" ... >
         <DESCRIPTION>Link to DataLink</DESCRIPTION>
*        <LINK content-type="application/x-votable+xml;content=datalink" 
*      </FIELD>

/Note: This basic LINK annotation is limited to the general case that 
all your URLs on a column return the same content-type. Thus, it is not 
usable for a Datalink VOTable content itself which can return mixed 
content-type results. In this case, just follow the Datalink 
recommendation (access_url + access_format columns)/


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