bullet1 Watch out   Concerns


bullet2 Effects of proliferation

Prolifieration of URI schemes works against interoperability


bullet2 Consistency of file: URI scheme

This is a misunderstood URI scheme, where the misunderstandings result in apparent inconsistencies.


bullet2 Application constraints on scheme types

Some applications or protocols may constrain allowable URI schemes, which appears to go against the idea of universality.


bullet2 URI form constraints

Some applications or protocols may constrain the form of allowable URI: e.g. no relative form or fragment identifiers allowed.


bullet2 Internationalization/ Unicode support


bullet2 URIs and QNames

Some XML applications, notable XML namespaces, adopt the idea of a base URI that references a collection of resources, and sub-URIs (path-children or fragment identifiers) that refer to members of the collection.  This combination of base URI and local name is referred to as a QName.