An 'info' URI with namespace 'bnf' takes the form:

info:bnf/<bnf-context>/<sub-context>

bnf-context

bnf-context = ALPHA *(ALPHA / DIGIT )

i.e. alphanumeric with leading alphabetic character.

Values of <bnf-context> correspond to naming authorities 
assigned by the national library of France and registered at
http://bibnum.bnf.fr/identifiants/bnFInfoURI.html.

sub-context

sub-context = sub-context-component *("/" sub-context-component) ["#" component]

sub-context-component

sub-context-component = pchar *(pchar)

The value of <sub-context-component> is an alphabetic string assigned 
by the national library of France and corresponding to the 
name of a specific data dictionary. 

component

component = pchar *(pchar) 

The value of <component> is an alphabetic string assigned 
by the national library of France and corresponding to the 
name of an element inside a specific data dictionary.

All data dictionaries are declared in the national library 
of France preservation system documentation. When 
applicable, they are published at http://bibnum.bnf.fr. 
Data dictionaries are expressed using a human readable 
format and can also be formalized according to a machine 
readable format such as XML schema, RDFS, OWL.


pchar (and others)

pchar is as defined in RFC 3986, that is:

pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded = "%" HEXDIG HEXDIG
sub-delims  = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

ALPHA, DIGIT, AND HEXDIG are as defined in RFC 2234: upper 
or lower case alphabetic (A-Z / a-z), decimal digit (0-9), 
and hexadecimal digit (DIGIT / "A" / "B" / "C" / "D" / "E" / 
"F") respectively.

Percent Encoded Characters 

Percent Encoded Characters are used in the rare cases where 
non US-ASCII characters appears in the URI.

All identifiers in the info:bnf namespace are case-sensitive.

The info:bnf is primarily used to assign URIs to classes 
and properties in data dictionaries that are intended to be 
expressed in RDF.

These URIs correspond to abstract concepts and they don't 
need to be actionable or to dereference a resource. The BnF 
is using another persistent identifier scheme (ARK) for 
resources that need to be dereferenced such as digital 
objects, web documents, etc.

The info URIs are meant to be easily readable for ease of 
use in the system (for instance, to construct a RDF 
ontology or to query it with SPARQL) so they are composed 
with semantic elements rather than opaque strings.

More information on the use of identifiers can be found at 
http://bibnum.bnf.fr/identifiants/index.html