We have used a very similar protocol to assemble the latest AVH cache. It should be noted that this is an as-well-as protocol that only works because we have an established semantic standard (hispid/abcd).
greg
trobertson@gbif.org wrote:
Hi All,
This is very interesting too me, as I came up with the same conclusion while harvesting for GBIF.
As a "harvester of all records" it is best described with an example:
- Complete Inventory of ScientificNames: 7 minutes @ the limited 200
records per page
- Complete Harvesting of records:
- 260,000 records
- 9 hours harvesting duration
- 500MB TAPIR+DwC XML returned (DwC 1.4 with geospatial and curatorial
extensions)
- Extraction of DwC records from harvested XML: <2 minutes
- Resulting file size 32MB, Gzipped to <3MB
I spun hard drives for 9 hours, and took up bandwidth that is paid for, to retrieve something that could have been generated provider side in minutes and transferred in seconds (3MB).
I sent a proposal to TDWG last year termed "datamaps" which was effectively what you are describing, and I based it on the Sitemaps protocol, but I got nowhere with it. With Markus, we are making more progress and I have spoken with several GBIF data providers about a proposed new standard for full dataset harvesting and it has been received well. So Markus and I have started a new proposal and have a working name of 'Localised DwC Index' file generation (it is an index if you have more than DwC data, and DwC is still standards compliant) which is really a GZipped Tab file dump of the data, which is slightly extensible. The document is not ready to circulate yet but the benefits section reads currently:
- Provider database load reduced, allowing it to serve real distributed
queries rather than "full datasource" harvesters
- Providers can choose to publish their index as it suits them, giving
control back to the provider
- Localised index generation can be built into tools not yet capable of
integrating with TDWG protocol networks such as GBIF
- Harvesters receive a full dataset view in one request, making it very
easy to determine what records are eligible for deletion
- It becomes very simple to write clients that consume entire datasets.
E.g. data cleansing tools that the provider can run:
- Give me ISO Country Codes for my dataset
- The application pulls down the providers index file, generates ISO
country code, returns a simple table using the providers own identifier
- Check my names for spelling mistakes
- Application skims over the records and provides a list that are not
known to the application
- Providers such as UK NBN cannot serve 20 million records to the GBIF
index using the existing protocols efficiently.
- They have the ability to generate a localised index however
- Harvesters can very quickly build up searchable indexes and it is easy
to create large indices.
- Node Portal can easily aggregate index data files
- true index to data, not an illusion of a cache. More like Google sitemaps
It is the ease at which one can offer tools to data providers that really interests me. The technical threshold required to produce services that offer reporting tools on peoples data is really very low with this mechanism. This and the fact that large datasets will be harvestable - we have even considered the likes of bit-torrent for the large ones although I think this is overkill.
As a consumer therefore I fully support this move as a valuable addition to the wrapper tools.
Cheers
Tim (wrote the GBIF harvesting, and new to this list)
Begin forwarded message:
From: "Aaron D. Steele" eightysteele@gmail.com Date: 13 de mayo de 2008 22:40:09 GMT+02:00 To: tdwg-tapir@lists.tdwg.org Cc: Aaron Steele asteele@berkeley.edu Subject: Re: [tdwg-tapir] Tapir protocol - Harvest methods?
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:
- download latest csv dump for a resource using the web service.
- flush all locally cached records for the resource.
- 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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