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Nod...<br>
<br>
We don't need a service... IMHO we write what we need, as simply as
we need it... and if the complexity grows past an upper bound, then
there is justification for using something else.<br>
<br>
On 3/9/12 2:00 AM, <a class="moz-txt-link-abbreviated" href="mailto:stephen.pascoe@stfc.ac.uk">stephen.pascoe@stfc.ac.uk</a> wrote:
<blockquote
cite="mid:7D87E6CC-D17D-4491-988B-A1894ECA4C9E@stfc.ac.uk"
type="cite">
<pre wrap="">My last email crossed in flight ...
</pre>
<blockquote type="cite">
<pre wrap="">So, to just make a quick shot in terms of PIDs/EPIC:
You'd rather assign identifiers to all the low-level entities and build up a hierarchy through aggregations. If the variables are corrected, you'd publish a new identifier for an extended version of the old collection (some cloning involved here, but still only on the identifier side), and where possible still reference the old variables as their data has not changed. If consequently done, this decouples the identification/publication of identifiers issue from the data layer, and that's one of the strong advantages I can see in a global PID infrastructure.
</pre>
</blockquote>
<pre wrap="">
These are Gavin's Merkel trees -- trees of hashes where each node is a hash of it's children.
The real challenge will be mapping such a system onto the current ESGF components.
S.
On 9 Mar 2012, at 09:51, Tobias Weigel wrote:
</pre>
<blockquote type="cite">
<pre wrap="">On 09.03.2012 10:31:28, Estanislao Gonzalez wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Making a hash that uniquely identifies all the information, like the one
you've proposed Stephen, is certainly appealing. Though we will have a
lot of hashes, most of them pointing to the same data from the user
perspective. For instance, the user download a variable and from that
point onwards, other variables got add and changed, catalogs get
republished unintentionally or moved to other machines, errors at all
stages get corrected, new access to the data get inserted to the
catalogs, etc (They do happen, I've done them all). I'd expect about 20
different hashes from it, none of them would be interesting to the user.
IMHO we need to find proper versioning units; the publication unit
(realm dataset) as we now use might not be the best option.
AFAICT everything moves in variable units (atomic datasets). My
publication tasks are very different, but it never matches the
publication unit we use.... hardly ever.
</pre>
</blockquote>
<pre wrap="">
>From the user's perspective, meaningful IDs (like the ones currently visible in the gateway, "cmip5.output1.MPI-M...") are preferable to hashes. However, from what you are writing here I'd think that such IDs can only be applied to very high-level entities and are useless for the actual data management. This could be addressed through collections/aggregations perhaps. In general, I'd be comfortable with hashes as Stephen originally proposed. I've never seen anyone complaining about git in this respect.
</pre>
<blockquote type="cite">
<pre wrap="">For example this is how publication looks from my perspective:
Normally I get information about a complete ensemble that was created
anew. No information on what was changed or not. Just the data (and the
computed checksums). I have to find out which datasets are there and how
they relate to the ones I've already published (i.e. I have to
distinguish between new, changed and deleted).
Then the other common tasks are, e.g., when a variable was wrongly
computed. So I get something like, "umo,vmo from 1pctCO2 are wrong and
will be recalculated". This requires me to extract the variables from
the datasets (finding out which), publish a new version without them and
when they are corrected, generated yet another new version to include
the corrected variables.
This generates 2 Versions without any meaning for those users interested
in other variables.
</pre>
</blockquote>
<pre wrap="">
So, to just make a quick shot in terms of PIDs/EPIC:
You'd rather assign identifiers to all the low-level entities and build up a hierarchy through aggregations. If the variables are corrected, you'd publish a new identifier for an extended version of the old collection (some cloning involved here, but still only on the identifier side), and where possible still reference the old variables as their data has not changed. If consequently done, this decouples the identification/publication of identifiers issue from the data layer, and that's one of the strong advantages I can see in a global PID infrastructure.
Best, Tobias
</pre>
<blockquote type="cite">
<pre wrap="">All the data I get is not related at all with the "realm" datasets (or
publication units). And this makes the data management more difficult.
I just think we might want to review what we need and distinguish the
bes units from three different perspectives: the producer (cmor), the
data manager (esg) and the user.
Once we know that for sure (and I doubt it will be the same unit for
all), then we can think about unique ids and a hashing procedure, which
I strongly support.
My 2c,
Estani
Am 09.03.2012 08:26, schrieb <a class="moz-txt-link-abbreviated" href="mailto:stephen.pascoe@stfc.ac.uk:">stephen.pascoe@stfc.ac.uk:</a>
</pre>
<blockquote type="cite">
<pre wrap="">Hi Gavin,
That would definitely help but I don't think it's sufficient. How many of us would notice if a centre republished the same dataset (same dataset_id and facet metadata) with different checksums? Estani would I expect :-) but the system itself wouldn't.
I would like to see a hash of invariants of each dataset used as identifiers. For that we'd need to strip-out all the information from a THREDDS catalog which might legitimately change without changing the data: URL paths, service endpoints, last-modified, etc., but keeping filenames, checksums and some properties. Canonicalise a serialisiation then generate a hash.
We'd also need to really keep track of these hashes. We have checksums and tracking_ids right now and are under-utilising them.
Cheers,
Stephen.
On 9 Mar 2012, at 05:05, Gavin M. Bell wrote:
Hello,
If we enforced checksums to be done as a part of publication, then this would address this issue, right?
On 3/8/12 8:39 AM, <a class="moz-txt-link-abbreviated" href="mailto:stephen.pascoe@stfc.ac.uk">stephen.pascoe@stfc.ac.uk</a><a class="moz-txt-link-rfc2396E" href="mailto:stephen.pascoe@stfc.ac.uk"><mailto:stephen.pascoe@stfc.ac.uk></a> wrote:
Tobias, sorry I miss-typed your name :-)
S.
On 8 Mar 2012, at 16:00,<a class="moz-txt-link-rfc2396E" href="mailto:stephen.pascoe@stfc.ac.uk"><stephen.pascoe@stfc.ac.uk></a><a class="moz-txt-link-rfc2396E" href="mailto:stephen.pascoe@stfc.ac.uk"><mailto:stephen.pascoe@stfc.ac.uk></a>
wrote:
Hi Thomas,
As you say, it's too late to do much re-engineering of the system now -- we've attempted to put in place various identifier systems and none of them are working particularly well -- however I think there is another perspective to your proposal:
1. ESG/CMIP5 is deployed globally across multiple administrative domains and each domain has the ability to cut corners to get things done, e.g. replacing files silently without changing identifiers.
2. ESG/CMIP5 system is so complex that who'd blame a sys-admin for doing #1 to get the data to scientists when they need it. Any system that makes it impossible, or even only difficult, to change the underlying data is going to be more complex and difficult to administer than a system that doesn't, unless that system was very rigorously designed, implemented and tested.
Because of #1 I'm convinced that a fit-for-purpose identifier system wouldn't use randomly generated UUIDs but would take the GIT approach of hashing invariants of the dataset so that any changes behind the scenes can be detected.
Because of #2 I'm convinced that now is not the time to start building more software to do this. We have to stabilise the system and learn the lessons of CMIP5 first.
Cheers,
Stephen.
On 8 Mar 2012, at 15:32, Tobias Weigel wrote:
Jamie/All,
these are important questions I have been wondering about as well; we just had a small internal meeting yesterday with Estani and Martina, so I'll try to sum some points up here. I am not too familiar with the ESG publishing process, so I can only guess that Stephen's #1 has something to do with the bending of policies that are for pragmatic reasons not enforced in the CMIP5 process. (My intuition is that *ideally* it should be impossible to make data available without going through the whole publication process. Please correct me if I am misunderstanding this.)
Most of what I have been thinking about however concerns point #2. I'd claim that the risk here should not be underestimated; data consumers being unable to find the data they need is bad ("the advanced search issue"), but users relying on deprecated data - most likely without being aware of it - is certainly dangerous for scientific credibility.
My suggestion to address this problem is to use globally persistent identifiers (PIDs) that are automatically assigned to data objects (and metadata etc.) on ESG-publication; data should ideally not be known by its file name or system-internal ID, but via a global identifier that never changes after it has been published. Of course, this sounds like the DOIs, but these are extremely coarse grained and very static. The idea is to attach identifiers to the low-level entities and provide solutions to build up a hierarchical ID system (virtual collections) to account for the various layers used in our data. Such persistent identifiers should then be placed prominently in any user interface dealing with managed data. The important thing is: If data is updated, we don't update the data behind identifier x, but assign a new identifier y and create a typed link between these two (which may be the most challenging part) and perhaps put a small annotation on x that this data is depreca
ted. A clever user interface should then redirect a user consistently to the latest version of a dataset if a user accesses the old identifier.
This does not make it impossible to use deprecated data, but at least it raises the consumer's awareness of the issue and lowers the barrier to re-retrieve valid data.
As for the point in time; I'd be certain that it is too late now, but it is always a good idea to have plans for future improvement.. :)
Best, Tobias
Am 08.03.2012 13:06, schrieb Kettleborough, Jamie:
Thanks for the replies on this - any other replies are still very welcome.
Stephen - being selfish - we aren't too worried about 2 as its less of an issue for us (we do a daily trawl of thredds catalogues for new datasets), but I agree it is a problem more generally. I don't have a feel for which of the problems 1-3 would minimise the risk most if you solved it. I think making sure new data has a new version is a foundation though.
Part of me wonders though whether its already too late to really do anything with versioning in its current form. *But* I may be overestimating the size of the problem of new datasets appearing without versions being updated.
Jamie
-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:go-essp-tech-bounces@ucar.edu">go-essp-tech-bounces@ucar.edu</a><a class="moz-txt-link-rfc2396E" href="mailto:go-essp-tech-bounces@ucar.edu"><mailto:go-essp-tech-bounces@ucar.edu></a>
[<a class="moz-txt-link-freetext" href="mailto:go-essp-tech-bounces@ucar.edu">mailto:go-essp-tech-bounces@ucar.edu</a>] On Behalf Of Sébastien Denvil
Sent: 08 March 2012 10:41
To: <a class="moz-txt-link-abbreviated" href="mailto:go-essp-tech@ucar.edu">go-essp-tech@ucar.edu</a><a class="moz-txt-link-rfc2396E" href="mailto:go-essp-tech@ucar.edu"><mailto:go-essp-tech@ucar.edu></a>
Subject: Re: [Go-essp-tech] What is the risk that science is
done using 'deprecated' data?
Hi Stephen, let me add a third point:
3. Users are aware of a new versions but can't download files
so as to have a coherent set of files.
With respect to that point the p2p transition (especially the
attribut caching on the node) will be a major step forward.
GFDL just upgrad and we have an amazing success rate of 98%.
And I agree with Ashish.
Regards.
Sébastien
Le 08/03/2012 11:34, <a class="moz-txt-link-abbreviated" href="mailto:stephen.pascoe@stfc.ac.uk">stephen.pascoe@stfc.ac.uk</a><a class="moz-txt-link-rfc2396E" href="mailto:stephen.pascoe@stfc.ac.uk"><mailto:stephen.pascoe@stfc.ac.uk></a> a écrit :
Hi Jamie,
I can imagine there is a risk of papers being written on
deprecated data in two scenarios:
1. Data is being updated at datanodes without creating a
new version
2. Users are unaware of new versions available and
therefore using
deprecated data
Are you concerned about both of these scenarios? Your
email seems to mainly address #1.
Thanks,
Stephen.
On 8 Mar 2012, at 10:21, Kettleborough, Jamie wrote:
Hello,
Does anyone have a feel for the current level of risk that
analysists
are doing work (with the intention to publish) on data
that has been
found to be wrong by the data providers and so deprecated (in some
sense)?
My feeling is that versioning isn't working (that may be
putting it a
bit strongly. It is too easy for data providers - in their
understandable drive to get their data out - to have
updated files on
disk without publishing a new version. How big a deal does anyone
think this is?
If the risk that papers are being written based on
deprecated data is
sufficiently large then is there an agreed strategy for
coping with
this? Does it have implications for the requirements of the data
publishing/delivery system?
Thanks,
Jamie
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Department of Data Management
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</pre>
</blockquote>
<pre wrap="">
</pre>
</blockquote>
<pre wrap="">
--
Tobias Weigel
Department of Data Management
Deutsches Klimarechenzentrum GmbH (German Climate Computing Center)
Bundesstr. 45a
20146 Hamburg
Germany
Tel.: +49 40 460094 104
E-Mail: <a class="moz-txt-link-abbreviated" href="mailto:weigel@dkrz.de">weigel@dkrz.de</a>
Website: <a class="moz-txt-link-abbreviated" href="http://www.dkrz.de">www.dkrz.de</a>
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Sitz der Gesellschaft: Hamburg
Amtsgericht Hamburg HRB 39784
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<br>
<pre class="moz-signature" cols="72">--
Gavin M. Bell
--
"Never mistake a clear view for a short distance."
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</pre>
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