[Uri-review] Allow identifying issues with ISSN NID

[Kristof Zelechovski <[e-mail]>]

Problem statement


The ISSN NID syntax, as defined in RFC 3044, does not allow to identify
specific issues of a serial publication.  It only identifies a serial
publication, as a set of past and future issues.  This is an abstract entity
and it is not in line with the prevailing URN practice that URN should be
used to name concrete resources and not sets thereof.  While the present
state of affairs is acceptable, the ability to identify specific issues is
missing.


Use case


The authorities of Republic of Poland publish the acts of law in a serial
publication called The Journal of Statutes with the corresponding URN
urn:ISSN:0867-3411.  It is common for Web content related to Polish law to
refer to individual acts of law contained within this publication; this URN
is not sufficient for the purpose.


Benefits


Allowing ISSN NID to refer to fragments of particular publications would
allow: 

*	content management systems - to supply the correct human-readable
reference to the fragment,
*	Web browser protocol handlers - to provide textual information about
the availability of the particular issue both in printed and downloadable
form.


Proposed Solution


Allow extended ISSN of the form urn:ISSN:0867-3411:2001:72#747, meaning year
2001, issue 72, position 747, where:

*         The format of the year part is four digits.  

*         The format of the issue number part is generally a number but it
depends on the publication; several publications have several versions of
the same issue with varying components; the versions are distinguished by an
alphabetic suffix appended to the issue number.  Formally, the issue number
can contain any characters allowed in an URI, except the reserved characters
as defined by RFC 3986 and the colon character ":", and can contain
percent-encoded characters in the UTF-8 character set.  The colon character
is not allowed because it is reserved for future development.  

*         The meaning of the fragment identifier depends on the particular
publication and it is not defined by the present specification.  The
fragment identifier is supposed to be the position number for scientific and
legal journals that maintain running position numbers, which constitute the
majority of use cases of references to serial publications.  It should also
be possible to address a range of pages within an issue using the syntax
urn:ISSN:0867-3411:2001:72#pages=247-259 ; this way of identifying a
fragment is deprecated when position numbers are provided by the editor.


Known problems


ISSN URN can resolve to electronic publications available in various media
types as well as printed publications.  The meaning of the fragment
identifier part as defined above is valid for printed publications only.  As
the interpretation of fragment identifiers is different for different media
types, the fragment identifier, if carried over from the ISSN URN without
reinterpretation, need not denote a valid fragment identifier in the sense
of the media type of the resource retrieved.  However, if the human reader
can see the identifier of the fragment that is being referred to, he can
find it in the retrieved resource by reading it as if it were a printed
publication.