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ivoa-std / DataLink

DataLink standard (DAL)
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Data link #52 #54

Closed Bonnarel closed 2 years ago

Bonnarel commented 3 years ago

This PR is proposed by Laurent and me. It introduces the description of the templating mechanism in service descriptor accessURL. It's related to issue #27. takes into account the recent Running meetings discussions

mbtaylor commented 3 years ago

"A templating mechanism is proposed" - this is not appropriate language for a standard. The text needs to specify in this and the preceding section that the accessURL value is a templated URL that must be interpreted according to RFC6570 (otherwise clients that don't do that will understand the wrong URLs for services that do specify templated URLs).

You can't use the "Fields:" prefix for namespacing, since it violates the RFC6570 syntax for variable naming (see the varspec production in RFC6750 section 2.3). For simplicity I would be in favour of just not namespacing here, on the grounds that the PARAM and FIELD names ought not to share any of the same names (either enforce that with a MUST or just note undefined behaviour in case that a variable name refers to both a FIELD and a PARAM in the same context).

Third example: the referenced fields are

<FIELD ID="RAJ2000" name="RAJ2000"  datatype="double" arraysize="1"/>
<FIELD ID="DEJ2000" name="DEJ2000"  datatype="double" arraysize="1"/>

and referenced as "{Fields:RAJ2000}{Fields:DEJ2000}". Thus it's not clear from the example whether the reference is to the name or ID attribute. Remove or rename the non-referenced attributes to clarify what's going on here. From the other example it looks like the name attribute is what's being referenced, but that is not explicitly written, please add some text to this effect. I suggest also adding some text that makes clear what the RFC6570 syntax restrictions are on substitution variable names (RFC 6570 section 2.3): essentially alphanumerics, period, underscore, and percent-encoded characters.

Note also that arraysize="1" should be removed from these FIELD elements, deprecated since VOTable 1.3 Erratum 3 (and also in VOTable 1.4).

The template "-c={Fields:RAJ2000}{Fields:DEJ2000}" is reported as expanding to "-c=250.456+27.863". Where does the "+" character come from in that expansion?

pdowler commented 2 years ago

Is it OK if we close this PR and start fresh after DataLink-1.1? I am pretty sure, at a minimum, the conflicts will be tough to manage without losing other work.

Bonnarel commented 2 years ago

OK with me for that

Bonnarel commented 2 years ago

Laurent ?

pdowler commented 2 years ago

closed this because it is now significantly out of date and issue deferred to 1.2