at berkeley we've recently prototyped a simple php program that uses an existing tapirlink installation to periodically dump tapir resources into a csv file. the solution is totally generic and can dump darwin core (and technically abcd schema, although it's currently untested). the resulting csv files are zip archived and made accessible using a web service. it's a simple approach that has proven to be, at least internally, quite reliable and useful.
for example, several of our caching applications use the web service to harvest csv data from tapirlink resources using the following process: 1) download latest csv dump for a resource using the web service. 2) flush all locally cached records for the resource. 3) bulk load the latest csv data into the cache.
in this way, cached data are always synchronized with the resource and there's no need to track new, deleted, or changed records. as an aside, each time these cached data are queried by the caching application or selected in the user interface, log-only search requests are sent back to the resource.
after discussion with renato giovanni and john wieczorek, we've decided that merging this functionality into the tapirlink codebase would benefit the broader community. csv generation support would be declared through capabilities. although incremental harvesting wouldn't be immediately implemented, we could certainly extend the service to include it later.
i'd like to pause here to gauge the consensus, thoughts, concerns, and ideas of others. anyone?
thanks, aaron
2008/5/5 Kevin Richards RichardsK@landcareresearch.co.nz:
I think I agree here.
The harvesting "procedure" is really defined outside the Tapir protocol, is it not? So it is really an agreement between the harvester and the harvestees.
So what is really needed here is the standard procedure for maintaining a "harvestable" dataset and the standard procedure for harvesting that dataset. We have a general rule at Landcare, that we never delete records in our datasets - they are either deprecated in favour of another record, and so the resolution of that record would point to the new record, or the are set to a state of "deleted", but are still kept in the dataset, and can be resolved (which would indicate a state of deleted).
Kevin
"Renato De Giovanni" renato@cria.org.br 6/05/2008 7:33 a.m. >>>
Hi Markus,
I would suggest creating new concepts for incremental harvesting, either in the data standards themselves or in some new extension. In the case of TAPIR, GBIF could easily check the mapped concepts before deciding between incremental or full harvesting.
Actually it could be just one new concept such as "recordStatus" or "deletionFlag". Or perhaps you could also want to create your own definition for dateLastModified indicating which set of concepts should be considered to see if something has changed or not, but I guess this level of granularity would be difficult to be supported.
Regards,
Renato
On 5 May 2008 at 11:24, Markus Döring wrote:
Phil, incremental harvesting is not implemented on the GBIF side as far as I am aware. And I dont think that will be a simple thing to implement on the current system. Also, even if we can detect only the changed records since the last harevesting via dateLastModified we still have no information about deletions. We could have an arrangement saying that you keep deleted records as empty records with just the ID and nothing else (I vaguely remember LSIDs were supposed to work like this too). But that also needs to be supported on your side then, never entirely removing any record. I will have a discussion with the others at GBIF about that.
Markus
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