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IETF URI Working Group                                        R. Denenberg
Internet-Draft                                                J. Kunze
draft-ietf-uri-url-irp-04.txt                                 D. Lynch
5 February 1996                                               Editors
Expires in six months

                  Uniform Resource Locators for Z39.50


1. Status of this Document

This document is an Internet-Draft.  Internet-Drafts are working documents
of the Internet Engineering Task Force (IETF), its Areas, and its Working
Groups.  Note that other groups may also distribute working documents as
Internet-Drafts.

Internet-Drafts are working documents valid for a maximum of six months.
Internet-Drafts may be updated, replaced, or obsoleted by other documents
at any time.  It is not appropriate to use Internet-Drafts as reference
material or to cite them other than as a ``working draft' or ``work in
progress.''

To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or
munnari.oz.au.

Distribution of this document is unlimited.  Please send comments to
jak@violet.berkeley.edu, or to the discussion lists uri@bunyip.com and
z3950iw@nervm.nerdc.ufl.edu.


2. Introduction

Z39.50 is an information retrieval protocol that does not fit neatly into
a retrieval model designed primarily around the stateless fetch of data.
Instead, it models a general user inquiry as a session-oriented, multi-
step task, any step of which may be suspended temporarily while the
server requests additional parameters from the client before continuing.
Some, none, or all of these client/server interactions may require
participation of the client user, depending only on the client software
(the protocol itself makes no such requirements).

On the other hand, retrieval of "well-known" data may be performed in
a single step, that is, with a degenerate Z39.50 session consisting of
exactly one protocol search request and response.  Besides the basic
search sub-service, there are several ancillary sub-services (e.g., Scan,
Result Set Delete).  Among the functions covered by combinations of the
sub-services, two core functions emerge as appropriately handled by two
separate URL schemes:  the Session URL and the Retrieval URL.

Using two schemes instead of one makes a critical distinction between a
Z39.50 Session URL, which opens a client session initialized for
interactive use by the user, and a Z39.50 Retrieval URL, which opens and
closes a client session to retrieve a specific information item.  Making
this distinction at the scheme level allows the user interface to reflect
it on to the user, without requiring the user interface to parse otherwise
opaque parts of the URL (consistent with current practice).


3. The Z39.50 Session URL

The Z39.50 Session URL may be informally described as providing the
mechanism to switch the user to a Z39.50 client application.

   -  Host is required.
   -  Port is optional, and defaults to 210.
   -  All other parameters are optional.
   -  The Z39.50 client will start a session to the specified host/port
      (alternatively, it need not explicitly start a session, but may
      instead utilize an already open session to the same host/port).
   -  A database must be included if docid is included.
   -  If docid is included, the client will perform the specified search
      (in the same manner as for the retrieval URL, specified below).
   -  If docid is not included, and other parameters (besides host/port)
      are specified, the client may use those parameters as "hints".
      Various clients may choose to treat them as requirements, or as
      preferences, or ignore them.
   -  In any case (whether a search is performed or not), the client will
      leave the Z39.50 session open for the user, to do retrievals, new
      searches, etc.  (This is the main distinction from the Retrieval URL
      which leaves it up to the client whether or not to keep the Z39.50
      session open.)


4. The Z39.50 Retrieval URL

The Z39.50 Retrieval URL is intended to allow a Z39.50 session to be used as
a transparent transfer mechanism to retrieve a specific information object.
A Z39.50 client uses information in the URL to formulate a Search Request.
The server's Search Response indicates how many records match the Request.
If the number of matching records does not equal one, the retrieval is
considered unsuccessful, and the client application's behavior is not defined.
If the number of matching records equals one, the server may have included
the desired record in the Search Response.  If not, the client requests
transmission of the record with a Present Request.  After the client has
received the specified record it may close the Z39.50 session immediately,
or keep it open for subsequent retrievals.

   -  Host is required.
   -  Port is optional, and defaults to 210.
   -  A database is required.
   -  The meaning of a retrieval URL with no docid is undefined.
   -  The docid is placed into a type-1 query, as the single term, in
      the general format (tag 45), using the Bib-1 attribute set, with
      a Use attribute value of docid, and a structure attribute of URx.
      The docid string is server-defined and completely opaque to the client.
   -  If element set name (esn) is not specified, it is the client's choice.
      If esn is specified, it should be used either in the Search
      request for the value of small- and/or medium- set-element-set-names
      or in a Present request following a Search.  These terms and their
      use are defined within the Z39.50 Standard [2].
   -  If record syntax (rs) is not specified, it is the client's choice.
      If one or more record syntaxes are specified, the client should select
      one (preferably the first in the list that it supports) and use it in
      a Search or Present request as the value of PreferredRecordSyntax.


5. BNF for Z39.50 URLs

The Z39.50 Session and Retrieval URLs follow the Common Internet Scheme
Syntax as defined in RFC 1738, "Uniform Resource Locators (URL)" [1].
In the definition, literals are quoted with "", optional elements
are enclosed in [brackets], "|" is used to designate alternatives,
and elements may be preceded with <n>* to designate n or more
repetitions of the following element; n defaults to 0.

z39.50url      = zscheme "://" host [":" port]
                      ["/" [database *["+" database]
                             ["?" docid]]
                           [";esn=" elementset]
                           [";rs=" recordsyntax *[ "+" recordsyntax]]]

zscheme        = "z39.50r" | "z39.50s"
database       = uchar
docid          = uchar
elementset     = uchar
recordsyntax   = uchar

Future extensions to these URLs will be of the form of [;keyword=value].

The following definitions are from RFC 1738. Between the Internet Draft
version and RFC 1738 two relevant changes were made: '=' was moved from
the <extra> character class to <reserved>, and <national> was removed from
the alternatives in <unreserved>. Neither <national> nor <punctuation> is
referred to in this document nor in RFC 1738.

lowalpha       = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
                 "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
                 "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
                 "y" | "z"
hialpha        = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
                 "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
                 "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"

alpha          = lowalpha | hialpha
digit          = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
                 "8" | "9"
safe           = "$" | "-" | "_" | "." | "+"
extra          = "!" | "*" | "'" | "(" | ")" | ","
national       = "{" | "}" | "|" | "\" | "^" | "~" | "[" | "]" | "`"
punctuation    = "<" | ">" | "#" | "%" | <">

reserved       = ";" | "/" | "?" | ":" | "@" | "&" | "="
hex            = digit | "A" | "B" | "C" | "D" | "E" | "F" |
                 "a" | "b" | "c" | "d" | "e" | "f"
escape         = "%" hex hex
unreserved     = alpha | digit | safe | extra
uchar          = unreserved | escape
xchar          = unreserved | reserved | escape
digits         = 1*digit

6. Security Considerations

The two Z39.50 URL schemes are subject to the same security implications
as the general URL scheme [1], so the usual precautions apply.  This means,
for example, that a locator might no longer point to the object that was
originally intended.  It also means that it may be possible to construct
a URL so that an attempt to perform a harmless idempotent operation such
as the retrieval of an object will in fact cause a possibly damaging
remote operation to occur.


7. Acknowledgements

The Z39.50 Implementors Group contributed the substance of this document.


8. References

   [1] Berners-Lee, T., Masinter, L., McCahill, M. (editors), "Uniform
       Resource Locators (URL)", RFC 1738, December 1994.
       ftp://ds.internic.net/rfc/rfc1738.txt

   [2] ANSI/NISO Z39.50-1994, "ANSI Z39.50:  Information Retrieval Service
       and Protocol", 1994.  ftp://ftp.loc.gov/pub/z3950/

   [3] ANSI/NISO Z39.50-1992, "ANSI Z39.50:  Information Retrieval Service
       and Protocol", 1992.
       ftp://ftp.cni.org/pub/NISO/docs/Z39.50-1992/www/Z39.50.toc.html
       (also available in hard copy from Omnicom Information Service,
       115 Park St., SE, Vienna, VA  22180).


7. Editors' Addresses

Ray Denenberg
Library of Congress
Collections Services
Network Development/MSO
Washington DC 20540
ray@rden.loc.gov
Voice: (202) 707-5795
Fax:   (202) 707-0115

John A. Kunze
Center for Knowledge Management
University of California, San Francisco
530 Parnassus Ave, Box 0840
San Francisco, CA  94143-0840
jak@ckm.ucsf.edu
Voice: (415) 502-6660
Fax:   (415) 476-4653

Denis Lynch
TRW Business Intelligence Systems
1329 Moffet Park Drive
Sunnyvale, CA 94089
dml@bis.trw.com
Voice: (408) 541-6418
Fax:   (408) 541-6401


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