Re: [urn] URI Scheme with Complex Equality Rules

["Randy Armstrong (OPC)" <[e-mail]>]

Hi Dale,

That was my original thinking if my proposed requirements are acceptable for a URN scheme.

Regards,

Randy

-----Original Message-----
From: Dale R. Worley <[e-mail]> 
Sent: Saturday, August 27, 2022 11:44 AM
To: Randy Armstrong (OPC) <[e-mail]>
Cc: [e-mail]
Subject: Re: [urn] URI Scheme with Complex Equality Rules

"Randy Armstrong (OPC)" <[e-mail]> writes:
> Specifically we need:

>   1.  Equality checks with case-insensitive string comparisons;
>   2.  Human readable strings with uniqueness provided by a DNS name or IP address (always lower case).
>   3.  A valid URI.
>   4.  R/Q/F components not allowed.
>
> We have been using urns of the form: urn:<dnsname>:<additional
> context>, however, this is not technically allowed by the URN RFC.
> We do not want a syntax that needs to be parsed before any comparison 
> can be done.

One simple approach would be to adjust the URN form you are using to

   urn:example:<dnsname>:<additional context>

You could pick what you choose in place of "example"; I notice that the namespace "opc" is available.

Given that it's a URN, the "urn" and "example" parts are required to be case-insensitive, but your specification can define the equality rule for the rest of it to be case-insensitive as well, but allow no other variation.  Having done that, comparing two URNs of this scheme becomes exact equality of the URNs as strings, except for being case-insensitive.

That seems to satisfy all your requirements with about the minimum change to your current practice.  Indeed, you can implement upward-compatibility between the previous and new usage by, whenever you see it, changing "urn:<something-that-is-not-example>:<stuff>" into "urn:example:<something-that-is-not-example>:<stuff>".

Dale