Where can I get an compact overview of RFC 2396?

Question

I want to understand RFC 2396 and the whole URL / URI thing better, and since NSURL from Cocoa is based on RFC 2396, I look for an overview. The RFC itself is too hard to read for me.

Answer 1

For an overview, the abstract and the introduction of the actual RFC should be sufficient. You can pick specific sections of the RFC out that you want to understand better.

Basically, to understand RFC 2396 better or more thoroughly - which is what you are asking (as well as an overview..), you can't do much better than reading the RFC itself to be honest. Seems logical to me.

Answer 2

I'm going to assume that your real question is about the whole URI / URL / URN split. And I'll start by saying that it's just terminology, and in many cases they're interchangeable.

A URL is a Uniform Resource Locator: it identifies an access "scheme", such as http:, and contains enough information to locate that resource using that scheme. It doesn't necessarily contain enough information to access the resource: For example, an HTTP URL will get you to a page, but that page may have authentication requirements for access.

A URN is a Uniform Resource Name: it also starts with a "scheme", then contains arbitrary information appropriate for that scheme. URNs are confusing because, while there are several predefined schemes such as "uuid", there's no specified use for those schemes (unlike, say, HTTP). This is not necessarily a bad thing: I like to use URNs for things like XML Namespaces, where I don't want there to be any implication that you can actually retrieve something related to that namespace.

A URI is a Uniform Resource Identifier: a superset containing URLs, URNs, and a few other identifier types. The RFC mentions URLs and URNs, but doesn't go into a lot of detail. That's because it focuses on the physical construction of a URI (the general format, how it should be encoded, &c), not the usage.

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Edit for the nitpickers: assume that when I say "starts with a scheme", there is the text "(which may be implied by current context)".

Answer 3

RFC 3305 might help:

This document [...] addresses and attempts to clarify issues pertaining to URIs. This document addresses how URI space is partitioned and the relationship between URIs, URLs, and URNs, describes how URI schemes and URN namespaces ids are registered, and presents recommendations for continued work on this subject.