[Dachs-support] Two questions on datalinking
Markus Demleitner
msdemlei at ari.uni-heidelberg.de
Thu Aug 26 09:02:08 CEST 2021
Hi Yan,
On Wed, Aug 25, 2021 at 12:53:56PM +0200, Yan Grange wrote:
> 1. Is there a way to communicate the information from the import to the
> datalink service, without necessarily putting it in a table that is visible?
> This is not secret information, but I just feel I do not want to confuse the
> casual visitor by having a table that basically stitches PIDs together (or
I think you're right there -- administrative information that cannot
reasonably be used by outside people generally shouldn't be shown to
them.
> links). One thing I was thinking of is using a (few) hidden column(s), or
> columns with very high verbosity. But maybe I am making the problem too hard
> and there is an easy fix here.
Well, if the information the datalink meta maker needs cannot be
computed from what's in the table already, you don't have much choice
but to add it there; you *could* store whatever extra information you
need in a separate text file, but in 99.9% of the cases that's a
worse choice in all of maintanability, performance, and amount of
code.
So, hidden columns look like the way to go for me.
This, by the way, *is* a good reason to upgrade to 2.4: It has the
//datalink#fromtable descriptor generator that makes it quite a bit
more straightforward to just pull a database row into a datalink
descriptor.
> 2. The main download link of the data then. I think I have three choices
> (basically what I want to bind the path to). The dlmeta, the dlget or a
> direct link to the remote data set. I find it hard to understand how much of
> a difference that makes in practice and whether or not there should be a
> preference for using either. Will Aladin be able to handle dlmeta links more
> or less transparently for instance?
So, last time I checked the mainstream Aladin didn't handle datalink
all that smoothly, but it's been a while. Still, I'd see two basic
cases:
(a) smallish data (up to ~1e8 bytes these days): Just put in the
direct link. Datalink-aware clients will still find datalinks
because there's a descriptor block, and if you want, you can put in
an extra datalink column as described at the end of
http://docs.g-vo.org/DaCHS/ref.html#integrating-datalink-services so
even browsers can see datalinks.
(b) largeish data (more than ~1e8 bytes these days): You probably
don't want to entice people to blindly download those, and so I'd
point to dlmeta. It'll not be immediately pretty, but when people
have to pull large amounts of data, it'll never be really pretty.
-- Markus
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