[DDI-SRG] Proposal for DNS-based DDI URN resolution and new DDI URN Syntax

[Joachim Wackerow]

Hi I-Lin,

It is good to hear from you. Thanks for your comments.

Please note that the proposal uses DNS as a generic distributed database 
system not just to look up IP numbers for IP names or the other way 
around. This approach is also used by voice-over-ip techniques like ENUM 
and SIP.

See my notes in the text below.

Additional thoughts welcome.

Achim

I-Lin Kuo wrote:
> 1) In both the examples
>     DDI URN "urn:ddi:gesis.de:3_1:Instance.s1786.4_3"  is resolved to 
> URL "http://repos.gesis.org/URN?urn:ddi:gesis.de:3_1:Instance.s1786.4_3" 
> by the DNS record
The NAPTR record points the URN (written as a DNS domain) just to an URI 
which is here an URL. No wildcards are used in this example, further 
resolution or other techniques (see the "u" flag of NAPTR). You will 
find similar records at ENUM where a phone number points to an 
voice-over-ip address.

>    
>     and the rewrite rule
>     <rewriteURI uriStartString="urn:ddi:gesis.de <http://gesis.de>" 
> rewritePrefix="http://repos.gesis.org/URN"urn:ddi:gesis.de 
> <http://gesis.de>"/>
"rewriteURI"  of XML catalog replaces just the defined prefix with 
another one. It is a simple string replacement, no resolution in a DNS 
sense. The resolver application which reads this XML catalog should 
accordingly map
"urn:ddi:gesis.de:3_1:Instance.s1786.4_3" to 
"http://repos.gesis.org/URN?urn:ddi:gesis.de:3_1:Instance.s1786.4_3"
The repository service at "http://repos.gesis.org/URN" should be able to 
give as response the object identified by the DDI URN.
(See the XML Catalog specification at 
http://www.oasis-open.org/committees/entity/spec-2001-08-06.html#s.rewriteuri)

When an application uses this service it has to do a regular DNS IP 
number lookup for repos.gesis.org. That shouldn't be a problem.

>    
>     the agency ID "gesis.de <http://gesis.de>" is somehow resolved to 
> "repos.gesis.org <http://repos.gesis.org>". Where is this resolution 
> defined? This would seem to me to involve an additional lookup into a 
> DDI agency resolver? It's better to simply use the appropriate domain 
> name or subdomain name in order to avoid this extra step (as well as the 
> creation of a DDI agency resolver)
> 
> 2) There's a conceptual confusion in what DNS is, as evidenced by the 
> statements:
> 
> "The DDI URN (new format)
> urn:ddi:maintaining-agency-id:ddi-version-number:name-of-maintainable-object.id-of-maintainable-object.object-version-number
> is related to the DNS name
> object-version-number.id-of-maintainable-object.name-of-maintainable-object.ddi-version-number.maintaining-agency-id.ddi.urn.arpa."
This is just a rewrite from one naming syntax (DDI URN) to another (DNS 
name). This should be done by the resolver application (client).

> 
> and
> 
> "A DNS name has a maximum length of 255 characters (including all dots)"
> 
> The DNS is a system for mapping readable hostnames to IP addresses. In 
> the narrowest sense of DNS, it simply maps domain names to ip addresses. 
As mentioned above the proposal uses DNS as a distributed database by 
means of the NAPTR records.

> As an example, with a URL such as 
> "http://repos.gesis.org/URN?urn:ddi:gesis.de:3_1:Instance.s1786.4_3", 
> the domain name of repos.gesis.org <http://repos.gesis.org> is resolved 
> to 216.24.138.156. Then the request is forwarded to the server at 
> 216.24.138.156, which decides what it wants to do with the rest of the 
> URL. The 255 octet limit only applies to the domain name 
> "repos.gesis.org <http://repos.gesis.org>", not to the entire URL. There 
> are practical limitations on the length of the entire URL, as browsers 
> may place limitations on the length of the URL, but those limits are 
> unlikely to be reached by DDI.
I would welcome when there is not a limitation on the names which are 
looked up in the DNS, but I'm not sure about that. The domain (at NAPTR 
the key, here the URN) seems to have the limitation of 255 octets (see 
http://tools.ietf.org/html/rfc3403#page-5). The URI (as replacement 
string in the NAPTR record) seems to have no limitation.

> 
> So, I'd recommend that a review of the meanings of URI, URN, and URL be 
> done, and a lot of the references in the document to "DNS" be replaced 
> by URL.
> 
> 3) Instead of resolving "urn:ddi:gesis.de:..." to 
> "http://repos.gesis.org/URN?...", I'd recommend that the resolution be 
> to "http://ddi.repos.gesis.org/...". While Apache can certainly rewrite 
> any URL, the first URL looks as if the main website server is doing the 
> resolution, while the second one looks as if there is a server dedicated 
> to DDI resolution.
I assumed that the web server of GESIS is www.gesis.org. 
ddi.repos.gesis.org is surely be clearer than repos.gesis.org. This is 
up to the institution which provides the service. Actually it could be 
also anything like xy.gesis.org or x.y.z.gesis.org

> 
> On Sun, May 24, 2009 at 2:32 AM, Joachim Wackerow 
> <joachim.wackerow at gesis.org <mailto:joachim.wackerow at gesis.org>> wrote:
> 
>     Attached are two documents on DNS-based DDI URN resolution and on a
>     new DDI URN syntax. Both documents are related.
> 
>     This proposal raises the question, how we can deal with this with
>     the background of the new version 3.1?
> 
>     Achim
> 
>     -- 
>     GESIS - Leibniz Institute for the Social Sciences
>     Postal address: P.O. Box 122155, 68072 Mannheim, Germany
>     Visiting address: B2 1, 68159 Mannheim, Germany
>     Phone: +49 (0)621 1246 262
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>     E-mail: joachim.wackerow at gesis.org <mailto:joachim.wackerow at gesis.org>
>     www.gesis.org/en/institute/ <http://www.gesis.org/en/institute/>
> 
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> 
> 
> 
> -- 
> I-Lin Kuo


-- 
GESIS - Leibniz Institute for the Social Sciences
Postal address: P.O. Box 122155, 68072 Mannheim, Germany
Visiting address: B2 1, 68159 Mannheim, Germany
Phone: +49 (0)621 1246 262
Fax: +49 (0)621 1246 100
E-mail: joachim.wackerow at gesis.org
www.gesis.org/en/institute/