The URI-space at http://id.ninebynine.org/ is reserved for use as identifier values of various kinds (e.g. XML namespaces, XML schema URIs, RDF schema URIs and who knows what else). For each identifier thus allocated, a retrievable document may be made available at this server. The document may be a text/HTML document, XML schema, RDF schema or some other document that describes the purpose and use of the identifier value in some way.
These identifiers may be used as protocol element identifiers in software designs.
Identifiers thus allocated will not be reassigned by the current owner of domain ninebynine.org.
Note: What do URIs identify?
Used for experimental work-in-progress identifier sets. Defined identifiers are not reused, but their definitions may be updated or changed or removed.
I'm not going to try and answer this question, which has been the subject of much debate in the WWW community. But my arrangement of http://id.ninebynine.org/ is an example of one possible answer to the question: if an http: URI identifies an abstract (non-web) resource, how does one identify the web page that is accessed by dereferencing the URI? My approach, in the absence of a more specific widely-held consensus is: use another URI.
I have chosen to use URIs of the form "http://id.ninebynine.org/..." to identify arbitrary concepts. Specifically, I mean the URI http://id.ninebynine.org/ to identify collection of things for which I have allocated such names. On dereferencing that URI using a web browser, a page (this page) is returned describing that intent. So how can I make assertions about this web page, for example that I am its author, distinct from the collection of things that are identified? My answer, at least until the web community finds a strong consensus on some other approach, is that the URI http://www.ninebynine.org/Ident identifies this web page. It happens that defererencing that URI returns the same sequence of bits that one gets by dereferencing http://id.ninebynine.org/, but my intent is that one represents a collection of resources and the other represents a web page.
In time, there may be (say) RDF documents that describe the resources denoted by these URIs, and I would expect to see assertions to the affect that the thing identified by http://id.ninebynine.org/ is a collection of some kind, and the thing identified by http://www.ninebynine.org/Ident is a web page. Thus, authomated processes may know that, even though they return the same representations when dereferenced directly, they do not denote the same things. Also, one day it may be possible that dereferencing the http://id.ninebynine.org/ form may return alternative representations more amenable for direct machine interpretation. Meanwhile, I operate at Tim Berners-Lee's level 2, Human readable, of language evolution [1], and all anyone gets is this web page.
I won't claim this is a perfect use of web features, but so far I've not found a practical situation in which it creates any significant problem.
[1] http://www.w3.org/DesignIssues/Evolution.html