Hi Mark, You are certainly right, URIs should and can't be compared and translated, really. They should be used as is. However, that is exactly the problem. To elaborate: our SAGA implementation binds to different middleware layers at runtime. As SAGA is supposed to abstract the middleware details away from the end user, that seems only sensible. What that means is, obviously, that I can do job submissions to different resources, utilizing different middleware beneath the hood: saga::job_server js_a ("broker_a.remote.net"); js_a.run_job ("/bin/date"); saga::job_server js_b ("broker_b.remote.net"); js_b.run_job ("/bin/date"); assume broker_a runs gram, broker_b runs unicore: that details stays hidden from the developer, and end user, as it should be. Now, URLs and URIs break that for file copies. saga::directory d_a ("gsiftp://server_a.remote.net//data/"); d_a.copy ("1.dat", "2.dat); saga::directory d_a ("ftp://server_b.remote.net//data/"); d_b.copy ("1.dat", "2.dat); In contrast to the job submission above, the end user must be aware that server_a runs gridftp, server_b does not. Although your statement is correct, it leaves that problem. Now, we could just ignore it, and leave the burden to the end user. That is what we did in GAT (which is similar to SAGA in some respect), but the end users have been rather unhappy about this, as that quite immediately destroys the flexibility the API otherwise provides. We also could rely on the availability of grid file systems, which removes that problem due to a global addressing scheme. However, GFS's are not widely deployed as of yet, so that would be overly idealistic. Or we can try to provide workarounds, and that is what the 'any' scheme is supposed to be, really. Its not a new scheme in fact, but a placeholder, which is supposed to be filled by any suitable scheme, if possible. we could also use ...://remote.host.net/tmp/file or such ;-) Hmm, I am not sure if I said anything different to the section in the intro really. Anyway, what I wanted to say is: You are right, mapping is not supposed to be possible. But the problem is that mappings are _very_ useful nevertheless... Cheers, Andre. PS.: sorry, I probably mix URLs and URIs all over the text. However, I think the problem holds for both. Quoting [Mark Mc Keown] (Jun 12 2006):
I have started looking at the SAGA strawman document and wanted to comment on the section "The URL problem".
URL -> URI ----------
In many circumstances URI has replaced URL, see for example Web Arch (http://www.w3.org/TR/webarch/). URIs allow you to identify things for which there may not yet exist a representation - for example an output file for job that has not started or http://host.net/tmp/file in the SAGA document.
Comparing URIs --------------
Rules for comparing URIs are scheme dependent, so you cannot compare a ftp URI to http URI, see http://www.textuality.com/tag/uri-comp-4 and http://www.faqs.org/rfcs/rfc2396.html. The SAGA document effectively says this but I am not sure there is any need to go beyond saying you cannot compare URIs from different schemes.
Two URIs with different schemes can identify the same resource, ie they are aliases, but you cannot tell this from comparing the URIs. However redirection may be used to relate the URIs. For example a HTTP redirect: a user may get a 3XX response when attempting to retrieve a representation of resource using HTTP which points him to a FTP server. So there is a question of how SAGA would handle a redirection - redirection of POST or PUT in HTTP requires user input.
any scheme ----------
The W3C recommends not inventing schemes, section 2.4 of Web Arch.
cheers Mark
-- "So much time, so little to do..." -- Garfield