Principles re: Universal Addressing

Use URIs
All important resources SHOULD be identified by a URI.
URI ambiguity
Ambiguity in the relationship between URIs and resources is harmful for humans and machines.
Resource descriptions
Owners of important resources (for example, Internet protocol parameters) SHOULD make available representations that describe the nature and purpose of those resources.
Safe retrieval
Agents do not incur obligations by retrieving a representation.
New URI schemes
Authors of specifications SHOULD avoid introducing new URI schemes when existing schemes can be used to meet the goals of the specifications.
Unregistered URI schemes
Unregistered URI schemes MUST NOT be used on the public Internet for general purpose applications.
Open issue: IRIs
When to use, when to convert, how to compare