DISCUSSION PAPER NO. 87

DATE: May 5, 1995
REVISED:

NAME: Addition of Subfield $l (Uniform Resource Locator) in Linking Entry Fields 76X-78X in the USMARC Bibliographic Format

SOURCE: Library of Congress

SUMMARY: This paper discusses a new subfield in the linking entry fields that would contain a Uniform Resource Locator (URL). This would provide a link to a related electronic item through an identification of the resource location on the Internet.

KEYWORDS: Subfield $l, in 76X-78X fields [Bibliographic]; Uniform Resource Locator [Bibliographic]

RELATED: 94-3 (Feb. 1994); DP86 (June 1995)

STATUS/COMMENTS:

5/5/95 - Forwarded to the USMARC Advisory Group for discussion at the June 1995 MARBI meetings.

6/25/95 - Results of USMARC Advisory Group discussion - Many participants had concerns about defining a subfield for a URL in the linking entry fields because: 1) the changeable nature of URL's would make it necessary to revise it not only in 856 fields but also in linking entry fields; 2) participants thought it preferable to include the URL in the related record and allow another link to that other record; 3) some were reluctant that it would encourage people to create links without creating a bibliographic record. It was not requested that this come back as a proposal.

DISCUSSION PAPER NO. 87: Addition of Subfield $l 
(Uniform Resource Locator) in Linking Entry Fields 76X-78X
                                         
I.       BACKGROUND

         With Proposal No. 94-3 (Addition of Subfield $u (Uniform
Resource Locator) to Field 856 in the USMARC Holdings/Bibliographic
Formats) a subfield was defined in field 856 (Electronic Location
and Access) to contain a URL, an electronic locator which is in
widespread use and was developed as a draft standard by the
Internet Engineering Task Force URI Working Group.  This element
was intended to be used when it is desired to specify a URL,
instead of parsing the data into the other subfields in the field
or in addition to the other data. Since the implementation of field
856 in many systems in late 1994 and early 1995, USMARC records
have been created using the field 856 (sometimes only the URL) to
link to the electronic item.  In some cases the field is in the
record for the original, with the 856 field linking to the
electronic version of the item described in the record; in other
cases the record is for an electronic item available remotely, with
the 856 field linking to that item.  In addition, it has been used
to link to a subset of the item (either in the record for the
original or the record for the electronic) by specifying the
portion of the bibliographic item to which the field applies in
subfield $3 (Materials specified).

         The USMARC bibliographic format contains the 76X-78X block of
fields for linking to related items and specifying the relationship
between them.  The 1994 edition of the USMARC Format for
Bibliographic Data explains:  
         "These relationships fall into two classes: 1) those related
         items that may assist the user in continuing to search but are
         not necessarily required in order to obtain the target item,
         e.g., former entries for serials, translations of the target
         item; 2) those related items that are required to obtain the
         target item (e.g., the host item for a component part)."
Some of the subfields in the linking entry fields are designed to
display a note in the record in which the field appears.  Much of
the information is descriptive in nature.  Other subfields provide
a machine linkage between the record for the target item and that
for the related item, if one exists.  Often the linking mechanism
is through a record control number in $w.

         It is desirable to include in the linking entry fields a
separate subfield for a Uniform Resource Locator (URL) to create a
machine linkage to a related electronic item.  The URL subfield
could provide a machine link to an item that does not have a
separate bibliographic record.  In addition it could provide
machine linkage to the related item without requiring the user to
go to the related bibliographic record to find the electronic
location information in field 856.  The following situations might
use the new subfield.  This is not a comprehensive list and other
situations will likely arise in the future:

         -       In records for a printed serial to link to the electronic
                 version using field 776 (Additional Physical Form Entry)
                 when the different versions are published simultaneously

         -       In records for a printed serial to link to the electronic
                 version using field 785 (Succeeding Entry) when the
                 printed serial ceases and is published only
                 electronically

         -       In records for a printed book to link to the SGML (or
                 other format) text

         -       In records for Internet resources to link to a related
                 resource (using any of the linking entry fields depending
                 upon what is appropriate)

The use of a linking entry field would allow for giving descriptive
information for the related item in the other available subfields. 
For instance, the field might include the title in $t and the URL
in the new subfield.

         The OCLC/NCSA Metadata Workshop held in Dublin, Ohio in March
1995 established a list of core elements (set of metadata) needed
for networked information discovery and retrieval.  One of the
elements is "Relation", defined as "important known relationship to
other objects ... this is where special relationships dealing with
versioning and edition should take place".  It specifies inclusion
of a type subelement to describe the nature of the relationship and
a scheme subelement to identify the notation used to identify the
related object.  The scheme could be the URL.  Thus, in order to
accommodate the recommendations of the Workshop in USMARC, a URL
subfield needs to be defined in the linking entry fields.  See
Discussion Paper No. 86 (Mapping of Dublin Metadata Element Set to
USMARC) for further discussion about the Workshop.


II.      ISSUES   

         Relation to field 856.  In defining a subfield for URL in the
linking entry fields, the question arises as to how it relates to
field 856.  One could link to the related item through the URL in
the linking entry field and bypass the 856 in the record for the
related item.  How does this affect how USMARC fields are used for
supplying version information? Couldn't a 776 field be used for
additional physical forms and not require the creation of a
separate record for the electronic version?  (Linking entry fields
do not require the creation of a record to which it is linked,
although this has been the common practice.)  Use of a 776 field
would not be practical if other information (e.g. compression
information, notes) that would be recorded in a field 856 is
needed.  It would be practical if additional bibliographic
information needs to be recorded in the linking entry field about
the related electronic item.
         
         What guidelines could be established to determine when to use
the URL in field 856 in the related record and when to use the URL
in the linking entry field?  An example that may cause confusion is
the situation where a record for an archival collection refers to
a related item, the electronic finding aid to the collection. 
Could this be considered a related item and the information
recorded in a 787 (Nonspecific Relationship Entry), or does it
belong in a field 856 with subfield $3 specifying that it is a
finding aid?

         Other location information.  There could be situations where
a linking entry field is appropriate but a URL is not available or
desirable for recording location and access information.  For
instance, the National Digital Library Program (formerly American
Memory) at the Library of Congress has digitized parts of LC's
collection and made them available through the LC World-Wide-Web
server.  The bibliographic record for the original contains a link
to the electronic version through field 856.  Because of the
volatility of location information (there is the potential of the
resource being moved from one machine to another or the compression
changed) only the unique elements are recorded in field 856, and
information in a document locator file supplies the additional
information for the specific item.  Typically only subfields $d
(Path), $f (electronic name) and perhaps $3 (materials specified)
are used with the access method in subfield $2 specified as "file". 
Does this type of situation where a URL is not available show a
need to provide other subfields in the linking entry fields?  Or
would it force the user to go to the record for the related item to
find the information in field 856?  

         URL versus URN.  There has been some concern about the
changeable nature of a locator and how it will be able to be
maintained in the future.  The Uniform Resource Name (URN) is also
under development within the URI Working Group of the Internet
Engineering Task Force.  The URN is intended to be a persistent,
location independent identifier for an object, providing a unique
element to identify it.  A resource identified by a URN may reside
at many locations under any number of filenames and may move any
number of times during its lifetime.  The URL identifies the
location for an instance of a resource identified by the URN.  The
URN is still under development and not all issues have been
resolved.  When it is finalized, it will provide bibliographic
control to uniquely identify a resource.  

         Since it is more desirable to use a permanent identifier to
link to the related item, should this new subfield be defined as
URI, allowing for either a URN or URL? This would require that the
wrapper "URN:" or "URL:" be used as data preceding the URN or URL. 
In previous discussions of field 856 it was suggested that "URL:"
not be used as data in subfield $u because it was not needed and it
caused a problem for machine linking using the http URL.  Or should
an additional subfield be defined for URN?  Since the linking entry
fields already contain subfield for unique identifiers ($w for
Record control number, $x for ISSN, $z for ISBN) a URN might be
more appropriate.  However, the standard is still under development
and URN's are not yet in widespread use.


III.  OPTIONS

         The following options might be considered.

         Option 1.  Define subfield $l in Linking entry fields 76X-78X
         for Uniform Resource Locator.  (Note that subfield $u has
         already been defined as Standard Technical Report Number)

         Option 2.  Define subfield $l in Linking entry fields 76X-78X
         for Uniform Resource Locator and subfield $q for Uniform
         Resource Name.

Guidelines need to be determined for when to use field 856$u and
when to use a linking entry field with $l.  

See Attachment A for a description of a possible subfield $l.
See Attachment B for possible examples of how the subfield might be
used.

------------------------------------------------------------------
                                                  ATTACHMENT A
76X-78X   Linking Entries -- General Information

        760       Main Series Entry
        762       Subseries Entry
        765       Original Language Entry
        767       Translation Entry
        770       Supplement/Special Issue Entry
        772       Parent Record Entry
        773       Host Item Entry
        775       Other Edition Entry
        776       Additional Physical Form Entry
        777       Issued With Entry
        780       Preceding Entry
        785       Succeeding Entry
        786       Data Source Entry
        787       Nonspecific Relationship Entry

Indicators

   First          Note controller
     0          Display note
     1          Do not display note

  Second

  760-777,
  786-787       Undefined
     #          Undefined

    780         Type of relationship
     0            Continues
     1            Continues in part
     2            Supersedes
     3            Supersedes in part
     4            Formed by the union of ... and ...
     5            Absorbed
     6            Absorbed in part
     7            Separated from

    785         Type of relationship
     0            Continued by
     1            Continued in part by
     2            Superseded by
     3            Superseded in part by
     4            Absorbed by
     5            Absorbed in part by
     6            Split into ... and ...
     7            Merged with ... to form ...
     8            Changed back to
Subfield Codes

                  Control subfields
     $3     Materials specified  (NR)   [773 only]
     $6     Linkage  (NR)
     $7     Control subfield  (NR)
                /0 - Type of main entry heading
                /1 - Form of name
                /2 - Type of record
                /3 - Bibliographic level

                  Descriptive information
     $a     Main entry heading  (NR)
     $b     Edition  (NR)
     $c     Qualifying information  (NR)
                 [all except 773]
     $d     Place, publisher, and date of
                publication  (NR)
     $g     Relationship information  (R)
     $h     Physical description of source  (NR)
     $j     Period of content  (NR) 
                  [786 only]
     $k     Series data for related item  (R)
                [all except 760 and 762]

     $m     Material-specific details  (NR)
     $n     Note  (R)
     $p     Abbreviated title  (NR)   [773 only]
     $s     Uniform title  (NR)
     $t     Title  (NR)

              Numbers/codes
     $e     Language code  (NR)   [775 only]
     $f     Country code  (NR)   [775 only]
     <$l    Uniform Resource Locator (R)>
     <$q    Uniform Resource Name  (NR)>?
     $r     Report number  (R)
          [all except 760, 762, and 777]
     $u     Standard Technical Report Number  (NR)
          [all except 760, 762, and 777]
     $v     Source contribution  (NR)
            [786 only]                                      
     $w     Record control number  (R)
     $x     International Standard Serial Number  (NR)
     $y     CODEN Designation  (NR)
     $z     International Standard Book Number  (R)
            [all except 760, 762, and 777]


DEFINITION AND SCOPE

        The linking entry fields contain data concerning related
items.  These fields specify the relationship between the related
bibliographic items.  These relationships fall into two classes: 
1) those related items that may assist the user in continuing to
search but are not necessarily required in order to obtain the
target item, e.g., former entries for serials, translations of the
target item; 2) those related items that are required to obtain the
target item (e.g., the host item for a component part).  The
linking entry fields are designed to display a note in the record
in which the linking entry field appears and to provide machine
linkage between the record for the target item and the record for
the related item, if one exists.

Definitions of terms used in descriptions of the linking entry
fields are:

        Target Item.  A bibliographic item that is the principal or
        primary unit for the description of which the record was
        constructed.  The target item is the item to which the data in
        character positions 06 (Type of record) and 07 (Bibliographic
        level) of the Leader apply.

        Related Item.  A bibliographic item that has either a
        chronological, horizontal, or vertical relationship with a
        target item, and for which the linking entry field is
        formulated.

        Component Part.  A bibliographic item that is physically part
        of another bibliographic item such that the retrieval of the
        part is dependent on the physical identification and location
        of the host item (e.g., a chapter in a book, an article in a
        journal).

        Host Item.  A bibliographic item that physically contains the
        component part described by the target item record (e.g., the
        book containing the described chapter, the journal in which
        the article appears).


        Chronological Relationship.  The relationship in time between
        bibliographic items (e.g., the relation of a serial to its
        predecessors and successors).

        Horizontal Relationship.  The relationship between versions of
        a bibliographic item in different languages, format, media,
        etc.

        Vertical Relationship.  The hierarchical relationship of the
        whole to its parts and the parts to the whole (e.g., a journal
        article to the journal, subseries to main entry series).

Record Links and Notes

        The record-linking technique in USMARC is described below.

* Linking Entry Fields (fields 760-787) -- These fields carry
          descriptive data concerning the related item, the control
          number for the record of the related item, or both.  Minimal
          content designation is provided for the data concerning the
          related item that is used in the linking entry fields.  For
          data operations requiring fuller content designation such as
          indexing and sorting, subfield $w (control number for the
          related item) allows the system to follow that link to the
          related record to obtain fully content-designated data. 
          Moreover, the coded data in control subfield $7 allows some
          types of indexing without reference to the actual related
          record.

* Linking Entry Complexity Note (field 580) -- The Linking Entry Fields
          are designed to support generation of a note concerning the
          related item in a display of the record for the target item. 
          When the relationship is too complex to be expressed using a
          display constant and the data from the linking entry field or
          the linked record, the note is recorded in the Linking Entry
          Complexity Note field.  When used, this field appears in
          addition to any relevant linking entry field.  The value used
          in the first indicator position of the linking entry fields
          determines whether a note is to be generated from the linking
          entry field or from field 580.

* Linked-Record Requirement (Leader/19) -- This data element indicates
          whether sufficient information is present in the linking
          entry field to support generation of an eye-legible note that
          identifies the related item or whether only a related record
          number is recorded.  If only a record number appears, the
          system will need to obtain the appropriate information from
          the related record to construct a standard display.

        The following subfields or subfield combinations are
        considered sufficient for display purposes:

        Subfield $a+$t               Main entry heading + Title
        Subfield $a+$s               Main entry heading + Uniform title
        Subfield $t                  Title
        Subfield $u                  Standard Technical Report Number
        Subfield $r                  Report Number

* Added Entries (fields 700-730) -- When an added entry is needed for
          a title used in a linking field, the added entry is recorded
          in the appropriate 700-730 field.  Linking fields are not
          intended take the place of added entries.  Likewise, an added
          entry in field 700-730 does not take the place of a linking
          field, as it cannot cause a note to be generated or carry a
          record link.

* Component Parts -- The linking entry field 773 (Host Item Entry) is
          used to link a target item that is an integral part of
          another item to the record for the other item.  For example,
          in records for journal articles it contains the
          identification of the journal.  In subfield $g of field 773,
          the exact location of the article in the journal is recorded.

------------------------------------------------------------------

                     ATTACHMENT B
                       Examples

Note that the following are serial examples.  It has not been
determined whether CONSER will decide to use the linking entry
subfield or whether 856$u will continue to be used.

Example 1.  Use of field 776 in record for print journal;
electronic journal published simultaneously.
Print version:
001         $a sn91-19114
022         $a 1053-1920
035         $a (OCoLC)23234647
245     00    $a Postmodern culture $b PMC : an electronic journal of
        interdisciplinary criticism $h [microform].
246     10    $a PMC
246     13    $a Postmodern culture journal
250         $a [Microfiche ed.]
260         $a [Raleigh, NC :$b Postmodern Culture],$c c1990-
310         $a Three times a year
362         $a Vol. 1, no. 1 (fall 1990)-
500         $a Eye-readable title: Postmodern culture journal.
515         $a Issue for fall 1990 called also Sept. 1990.
530         $a Available also on electronic mail (INTERNET and
            BITNET) and on computer disk.
650     #0    $a Postmodernism $x Periodicals
776     1   $t Postmodern culture $w (OCoLC)22471982
            $w(DLC)sn90003259 
            $l gopher://jefferson.village.Virginia.edu:70/00/pubs/pmc

Electronic version:
001         $a sn90-3259
022         $a 1053-1920
035         $a (OCoLC) 22471982
210     0   $a Postmod. cult.
222     #0    $a Postmodern culture
245     00    $a Postmodern culture : $bPMC :$ban electronic journal
              of interdisciplinary criticism $h[computer file]
246     10    $a PMC
260         $a Raleigh, NC :$bPostmodern Culture,$c1990-
265         $a Postmodern Culture, Box 5657, Raleigh, NC 27650
310         $a Three no. a year
350         $a Free (electronic mail) $a$30.00 (institutions,
            microfiche or disk) $a$15.00 (individuals, microfiche or
            disk)
362     0   $a Vol. 1, no. 1 (fall 1990)-
500         $a Mode of access: Electronic mail on INTERNET and
            BITNET.
500         $a Description based on surrogate.
530         $a Available also on microfiche and computer disk.
776     1   $t Postmodern culture $w(OCoLC)23234647 $w(DLC)
            sn91019114
856     7   $ugopher://jefferson.village.Virginia.edu:70/00/pubs/pmc
            $2gopher

Example 2: Print publication published simultaneously; multiple
856 fields.
Print version:
001         $asn94-7041
022         $a1080-6040
035         $a(OCoLC)31848353
130     0   $a Emerging infectious diseases (Print)
222     #0    $aEmerging infectious diseases $b(Print)
245     00    $aEmerging infectious diseases.
246     10    $aEID
260         $aAtlanta, GA :$bNational Center for Infectious Diseases,
300         $a v.
310         $a Four times per year
350         $a Free
580         $aPrint version of: Emerging infectious diseases
            (Online).
710     20    $a National Center for Infectious Diseases (U.S.)
776     1     $tEmerging infectious diseases (Online) $x1080-6059
              $w(DLC)sn95007042 $w(OCoLC)31949043
              $lftp://ftp.cdc.gov/pub/EID
              $lhttp://www.cdc.gov/ncidod/EID/eid.htm 

Electronic version:
001         $a sn95-7042  
022     0   $a 1080-6059  
037         $b Centers for Disease Control and Prevention, 1600
            Clifton Rd., Mailstop C-12, Atlanta, Ga 30333.
            Email:eideditor@cidod1.em.cdc.gov $c Free
130     0   $aEmerging infectious diseases (Online)  
222     0   $aEmerging infectious diseases $b (Online)  
245     00    $aEmerging infectious diseases $h [computer file] :
              $b EID.  
246     30    $aEID  
260         $aAtlanta, GA : $b National Center for Infectious
            Diseases, Centers for Disease Control and Prevention
            (CDC), $c[1995- 
310         $aFour times per year  
362     0   $aVol. 1, no. 1 (Jan.-Mar. 1995)-
538         $aMode of access: Internet email, FTP, and World Wide
            Web.
500         $aDescription based on hypertext version as viewed over
            the World Wide Web; title from homepage.
516     8   $aAvailable in ASCII, Adobe Acrobat, and PostScript file
            formats
580         $aOnline version of: Emerging infectious diseases
            (Print).  
710     2   $aNational Center for Infectious Diseases (U.S.)  
776     1   $t Emerging infectious diseases (Print) 
            $w (DLC)sn95007041 $w (OCoLC)31848353  
856     0   $alist.cdc.gov $h lists $i subscribe EID-<format>
            $z<format> refers to ASCII, PDF, or PS selection made by
            subscriber
856     1   $aftp.cdc.gov $d pub/EID $l anonymous
856     7   $u http://www.cdc.gov/ncidod/EID/eid.htm $2 http


Example 3: Library of Congress World Wide Web Home Page

001     95888888
040     $aDLC $cDLC
245     00$a Library of Congress World Wide Web Home Page
260     $a Washington, DC :$b Library of Congress,$c 1994-
505     0#$a About the Library and the World Wide Web -- Exhibits
        and Events -- Services and Publications -- Digital Library
        Collections -- LC Online Systems -- Congress and government
610     20$a Library of Congress$xInformation services.
650       #0$a Library resources $z United States
650       #0$a Wide Area Networks (Computer Networks)
710       2$a Library of Congress.
856       7$u http://lcweb.loc.gov $7http

001     95888889
040     $aDLC $cDLC
245     00$a LOCIS, Library of Congress Information System.
246     3#$a LOCIS
246     30$a Library of Congress Information System
260     $a Washington, DC :$b Library of Congress,$c 1968-
300     $a records <26+ million>
307     $a M-F 6:30 AM to 9:30 PM, Sa 8:00 AM to 5:00 PM Su 1:00 PM
        to 5:00 PM; closed on national holidays 
310     $a Updated daily
520     $a A conglomeration of files containing more than 26 million
        records, the earliest of which was created in 1968.
610     20$a Library of Congress$xInformation services.
710     2 $a Library of Congress.
773     0#$t Library of Congress World Wide Web Home Page 
        $l http://lcweb.loc.gov $w95888888
856     2$u telnet://locis.loc.gov

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