DATE: May 1, 1997

NAME: Use of the universal code character set in MARC records

SOURCE: MARBI Character Set Subcommittee

SUMMARY: This proposal suggests a preferred technique for encoding MARC data using a repertoire of characters from the universal character set (ISO 10646 (UCS)) to which the existing USMARC character sets have been mapped.

KEYWORDS: Character sets; Field 066 (Character Sets); ISO 10646; Linkage; Repertoire or script; Subfield $6 (in various fields); Subfield $b (066); UCS; Universal coded character set

RELATED: 96-10 (May 1996); DP 73 (December 1993)


5/1/97 - Forwarded to USMARC Advisory Group for discussion at the June 1997 MARBI meetings.

6/28/97 - Results of USMARC Advisory Group discussion - Option 1 for the mapping of the ASCII clones to the unified repertoire in the UCS was approved. The remaining changes were not approved pending the establishment of a follow-on technical committee to consider especially technical aspects for the identification of character codes used in records in the online environment.

8/21/97 - Result of final LC review - Agreed with the MARBI decision.

PROPOSAL NO. 97-10: Use of the universal code character set


For many years interest in a single universal coded character set
to replace all other character sets has been growing.  An
international standard set, ISO 10646 (Universal Coded Character
Set, or, UCS) is generally accepted as a good candidate for
eventual replacement for the 7 and 8-bit character sets now in
use.  The library community has shared this interest in a
universal coded character set and it first addressed the
possibilities with USMARC in 1993.

The MARBI Character Set Subcommittee was formed in June 1994 as a
result of Discussion Paper No. 73 (UCS and USMARC Mapping).  The
Subcommittee was asked to do the following: 1) review the
character set issues related to mapping between the repertoires
of the existing USMARC character sets and the universal set;
2) formulate a proposal that covers how universal character set
encodings might be used in USMARC records; and 3) identify other
issues related to character sets which need to be addressed by
MARBI and/or the library community.

During the past three years the Subcommittee reached consensus on
a mapping to the universal set for most of the characters in the
existing USMARC sets.  It also developed preferences for dealing
with certain mapping issues and revealed the need to add a small
number of characters to the existing USMARC sets.  This paper
presents those preferences and proposes a technique for encoding
characters from the universal character set repertoire in USMARC
records.  It also presents issues which MARBI may wish to
investigate further.

Mappings Completed

There are currently eight graphic and two control character sets
defined for use in USMARC records.  The graphic sets are basic
and extended sets for the Latin, Arabic, and Cyrillic scripts, a
basic set for the Hebrew script, and an extensive set of
ideographic (non-alphabetic) characters for East Asian languages
(i.e., Chinese, Japanese, and Korean, "CJK").  USMARC also
provides a special character encoding technique for a small
repertoire of superscript, subscript characters and three Greek
symbols that can appear in bibliographic data.  The USMARC
control character sets consist of a basic set with four control
characters and an extended set with two control characters.  The
control sets can be used with any of the graphic sets, although
some control characters are only meaningful for certain scripts
(e.g., joiner and nonjoiner are only used with Arabic script).

The task of mapping the characters in these USMARC character sets
to the unversal character set was carefully done following four
working principles:

    -   Round-trip mapping would be provided between USMARC
        characters and characters in the universal set wherever

    -   Transliteration schemes that rely on the USMARC character
        sets would remain unchanged unless no equivalent
        character in the universal set could be found, in which
        case a change to the transliteration schemes might be
        suggested to ALA and LC;

    -   Modified letters (that is, letters with associated
        diacritical marks or vocalization marks) would continue
        to be encoded as a base-letter with an accompanying
        combining character;

    -   Character codes in the private use space of the universal
        set would be used only if necessary to facilitate
        round-trip mapping.

The Subcommittee was able to map most of the characters in the
existing USMARC sets to unique character code values in the
universal set.  The mapping of these characters was approved by
MARBI as part of Proposal 96-10 (USMARC Character Set Issues and
Mapping to Unicode/UCS).  These mappings are available from LC's
MARC web site at: //  A
mapping of the USMARC "CJK" set to universal character set codes
is not yet available, but a subcommittee is being formed to
consider that task.  The subcommittee will use a mapping produced
by the Unicode Consortium as the basis for the USMARC mapping.


Treatment of the ASCII Clones

Round-trip mapping of a small subset of USMARC characters,
referred to as the "ASCII clones", mostly numbers, punctuation
marks, and special symbols shared by more than one script, was
problematic.  MARBI was unable to reach consensus at the time
Proposal 96-10 was discussed and the portion of the proposal
dealing with the ASCII clones was sent back to the character set
subcommittee for reexamination.

At the February 1997 meeting of the subcommittee various options
were considered, each of which had advantages and disadvantages
relating to the ability to return to the original USMARC encoding
of one of the ASCII clone characters once conversion of data to
one of the universal character set encodings had been performed. 
The problem is that the basic USMARC character set for each
script includes its own set of ASCII clones.  In the universal
set these are unified into a single repertoire of numbers,
punctuation marks, and special symbols.  The mapping of USMARC
characters to the universal set would be "many-to-one", making
exact reversability back to the USMARC sets impossible, unless
special characters were defined in the private use space.

The Subcommittee was unable to reach consensus on a solution and
has thus forwarded to MARBI the following options.  Two options
were formulated to resolve the problem.  A description of each
option, including advantages and disadvantages, follows.

Option 1: Map USMARC ASCII clones to a unified repertoire in
    the universal set


    1.  Mappings are to universally defined characters only, thus
        off-the-shelf products could be used by USMARC users and
        systems outside the USMARC community would have no
        difficulty interpreting USMARC data.

    2.  There would be no complications in the use of standard
        print and display drivers designed to work with character
        encodings from the universal set.

    3.  Other data originally created using character codes from
        the universal set is likely to use the ASCII clone
        characters rather than character codes from the Private
        User Space.

    4.  Future databases would not be cluttered with special
        characters which had a meaning only in an older system


    1.  The original USMARC encodings for ASCII clone characters
        might be lost after conversion to universal character set
        encodings unless an adequate algorithm could be developed
        to restore the original USMARC character values.  (It has
        been suggested that such an algorithm cannot be
        developed.)  This problem would be particularly serious
        for non-Latin character strings beginning with one of the
        ASCII clone characters.

    2.  The handling of bi-directional text may be more complex
        for character strings converted back into the USMARC
        character encodings.  Conversion and ordering of numeric
        strings may be problematic.

Option 2: Precede each ASCII clone by a script flag character
    defined in private use space


    1.  The original USMARC character set from which the ASCII
        clone came could be easily identified by the script flag
        character, thus facilitating conversion back to the
        original USMARC encoding.

    2.  The handling of bi-directional text may be simpler for
        character strings converted back into the original USMARC
        character encodings.

    3.  If later there is no need for perfect reversability, the
        script flags could be dropped from records, leaving data
        encoded as it would be with Option 1.


    1.  Records created originally within systems using one of
        the universal sets would need to use script flag
        characters defined in the private use space for all ASCII
        clones or the data would be incompatible with data
        converted from USMARC encodings.

    2.  USMARC-based library systems and databases would included
        encodings different from the standard encodings using the
        universal sets.  This would create a "library dialect" of
        the universal character set.

Technique for Using Characters from the Universal Set in USMARC

The second important charge of the Character Set Subcommittee was
to develop a technique for using characters from the universal
coded character set in USMARC records.  The Subcommittee
unanimously opposed the notion of mixing characters from the
existing USMARC sets and characters from one of the universal set
in a single USMARC record.  What remained was to develop a
technique that would fit within the USMARC structural framework
and accommodate the character set mappings proposed.  To fully
understand the proposed USMARC universal character encoding
technique, several assumptions have to be made about the

    1)  The MARC record structure (ANSI/NISO Z39.2 or ISO 2709)
        would not change.  Records would continue to be
        structured the way they always have been, with a
        24-character Leader, 12-character Directory entries,
        fixed-length and variable-length fields identified by
        alphanumeric field tags, alphanumeric subfield codes, and
        indicator positions in all non-control fields.

    2)  For USMARC records encoded using the universal character
        sets, a character would be defined as 16 consecutive bits
        instead of eight.  This would allow the definition of the
        length and address portions of the USMARC Leader and
        Directory (which contain values that indicate character
        counts) to remain unchanged.

    3)  Encoding of letters modified by diacritics would make use
        of the combining (non-spacing) characters, encoded
        following the base letter with which they were
        associated.  This would represent a change in the order
        of encoding of combining characters which are currently
        encoded preceding the base letter with which they are
        associated.  NOTE: Precomposed (letter-with-diacritic)
        characters defined in the universal character set would
        not be allowed in USMARC.

    4)  Since all scripts would be accommodated by a single
        character set, the locking escape sequences currently
        used in conjunction with latin and non-latin scripts in
        USMARC records would no longer be needed and could be
        dropped during conversion to universal character
        encodings.  They would need to be generated during
        conversion back to the USMARC sets.

These assumptions offer various advantages to USMARC users. 
Primary among the advantages would be that there wouldn't be
great differences between MARC records encoded with the existing
USMARC character sets and the universal set except for the
character encodings themselves.  The overall structure of the
data would not be affected.

The restriction of USMARC records to either all universal
character encodings or none would make processing of USMARC data
easier.  The character set used in records could be identified
systematically by the presence or absence of binary zeros as the
first eight bits in the record.  This implicit character set
identifier would be the result of the configuration of the first
five characters in every MARC record.  The first five characters
in a record indicate the record length, represent by numeric
characters 0 through 9.  In the universal character sets, numeric
characters 0 through 9 have binary zero as the first eight bits. 
In the existing USMARC sets, the first eight bits are never all
binary zero.  Binary zero is not allowed anywhere in USMARC
records encoded using the existing 8-bit USMARC character sets. 
Although not all universal set characters have binary zero as the
first eight bits, this 8-bit sequence of binary zeros would
always occur at the beginning of a recorded encoded with the
universal character set.  It could serve as an implicit flag. 
Recognition of this implicit flag could be designed into USMARC
systems to handle the import of records using both old and
new-style encodings.

Identification of Repertoire or Script

Since locking escape sequences would no longer be used to envoke
character set changes in USMARC records, the use of field 066
(Character Sets Present) needs to be examined.  The current
configuration of field 066 is as follows:

   066  Character Sets Present
    Indicators  (both are undefined and contain blank (#))
        $a   Non-ASCII GO default character set designation  (NR)
        $b   Non-ANSEL G1 default character set designation  (NR)
        $c   Alternate graphic character set idntification  (R)

The definition of the field could be expanded to allow the
identification of character sets by more than an escape sequence. 
It might also be useful to identify early in the record what
portions of a universal character set repertoire are present in
the record.  This could be done using new subfields in field 066;
subfield $d (Character set identifier) and subfield $e
(Repertoire).  These would carry codes that identify the base
character set and the repertoires from which characters found in
the record have been taken.  The repertoire codes could be based
on ISO 10646 Annex A (Collections of Graphic Characters for
Subsets) which provides a list of numeric codes for logical
repertoires.  The new subfield for repertoire could also contain
codes assigned to repertoires that relate to the existing USMARC
character sets, if this would be useful or necessary.  It would
be repeatable to identify multiple repertoires present.

Example:  066  ##$ducs$e1$e7$e10

    This example illustrates the identification of ISO 10646 in
    subfield $d and codes that identify the basic Latin and
    combining diacritical marks ("1" and "7") and Cyrillic ("10")
    repertoires of ISO 10646 (UCS) in repetitions of subfield $e.


The following is presented for consideration:

    -   Treatment of ASCII clones:

        Option 1: Map the USMARC ASCII clones in the Arabic,
             Cyrillic, and Hebrew sets to the unified
             repertoire in the universal coded character set
             (ISO 10646)

        Option 2: Same as option 1, also define script flag
             characters for Arabic, Cyrillic, and Hebrew in
             private use space to be used in conjunction with each
             occurrence of an ASCII clone character in Arabic,
             Cyrillic, and Hebrew character strings

    -   Establish that USMARC records employing character codes
        from the universal character set would use only those
        listed in the USMARC to UCS mapping and the existence of
        binary zeros in the first eight bits of a record will be
        an indicator for universal character set encoding.

    -   Define subfield $d (Character set) in field 066 to allow
        for a code that indicates the universal coded character

    -   Define a repeatable subfield $e (Repertoire) in field 066
        for indicating the subset of universal characters which
        can be expected in the MARC record.  A new USMARC list of
        repertoire codes would be established or ISO 10646 Annex
        A could be used.


The development of a proposal to allow the use of a universal
character set in USMARC records raises questions about the
scripts currently supported in USMARC and how non-Latin data is
usually  represented.  At present, USMARC only supports the
encoding of information in the "vernacular" (i.e., original
script) for languages that use the Arabic, Cyrillic, Hebrew, and
Latin script, or the Chinese/Japanese/Korean writing systems. 
Currently, all other languages must be represented by
transliterations of the vernacular script into the Latin script. 
The availability of character repertoires in the universal
character sets for a majority of modern writing systems (e.g.,
Greek), not to mention plans to add repertoires of characters for
numerous archaic writing systems (e.g., Glagolitic), allows
USMARC to expand the approved repertoires to encompass all

Prior to MARC, the Library of Congress and other libraries
produced printed catalog cards which included a variety of non-
Latin scripts.  Only with the switch to machine-readable
cataloging records in the 70's did this vernacular cataloging
give way to fully transliterated cataloging using only Latin
script characters.  The switch to fully transliterated cataloging
was intended to be temporary until technology permitted input of
vernacular scripts.  Systems have slowly begun to offer non-Latin
scripts.  The approval of a technique for using universal
character set encodings suggests that this may be the time for
MARBI to consider widening the scope of non-Latin character set
use for USMARC.  MARBI needs to consider what other scripts might
be usefully permitted in USMARC records, using characters from
the universal set, and the impact of such a change.

Related to the issue of non-Latin character set use in USMARC
records is the USMARC technique for recording alternate graphic
representations.  USMARC currently provides a technique for
recording alternate graphic representations of cataloging data
using repetitions of often non-repeatable variable USMARC fields. 
Repetitions of fields such as 100, 245, and 260  are carried in
occurrences of field 880 (Alternate Graphic Representation). 
Alternate graphic representations in occurrences of field 880 are
linked to Latin script transliterations in regularly tagged
fields using subfield $6 (Linkage).  This technique has been used
in a relatively small subset of all USMARC implementations, the
most important of which is maintained by the Research Libraries
Group.  RLG's RLIN database includes thousands of USMARC
bibliographic records that include information in the original
script linked to fully transliterated data.  This technique was
implemented to allow for the production of vernacular records for
systems that can handle them, and records with fully
transliterated data for other systems.

The adoption and implementation of USMARC in countries where all
information is in one non-Latin script (e.g., Russia) has not
required the use of 880 fields and transliterations. 
Incompatibilities between USMARC records from, for example
Russia, where non-Latin script data is recorded in regular
variable fields and records (like those in RLIN) in which
vernacular data is carried in occurrences of field 880, suggest
that the alternate graphic representation technique may not be
well suited for global use of USMARC.  Even internally, RLG does
not carry alternate graphic representations in 880 fields but
rather associates vernacular data with transliterations in
parallel occurrences of the regular variable fields.  MARBI may
want to consider making changes to the field 880/subfield $6
technique.  One alternative is to use subfield $6 to identify
repertoire/script only and use the newly-defined subfield $8
(Field link and sequence number) to handle related
representations of the information.

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