A distributed union catalogue is envisaged as a network of bibliographic systems that cooperate to enable their users to discover sites that hold copies of known items. Some of the participating systems will be traditional union catalogues; others will be single sites with comprehensive collections; others will be local or regional resource sharing systems. These systems are presumed to have resource sharing arrangements, which may be formal or informal.
Typically a user of the distributed union catalogue will approach it with a known item for which locations are required in order to initiate an inter-library loan request or a personal visit to obtain the item. The focus of the system is therefore on searches for known items, normally via a control number such as an ISBN or LCCN or via name and/or title. The ultimate retrieval goal is not primarily bibliographic information, but rather location, and if possible, availability information. Bibliographic information is used primarily to verify that retrieved items are in fact those sought for.
A principal goal of the distributed union catalogue is therefore to allow the user to obtain a useful number of locations for an item with a minimal number of searches. It is not seen to be a goal to enable the user to discover a comprehensive set of locations, merely a sufficient number to allow the user a good chance of being able to obtain the item through inter-library loan processes.
The retrieval of location information is therefore central to the distributed union catalogue. Unfortunately, the standard vehicle for transferring catalogue records, the MARC record, raises a number of issues in using Z39.50 for transferring location information. The USMARC manuals define separate formats for bibliographic information and holdings information. Under some circumstances fields defined for holdings are permitted to be embedded within a MARC bibliographic record, but when there is any level of complexity of description, as, for instance, in enumerating serial holdings for multiple copies, holdings information must be placed in separate holdings records that are linked with a bibliographic record.
The bibliographic record contains one field, 850, that can be used to carry identifiers of institutions that hold the item. No other information is carried in this field. This field, which is repeatable in the bibliographic record, can be used to carry hundred or even thousands of locations if required. While this basic location information is often adequate to enable monographs to be borrowed on inter-library loan, it does not provide a mechanism for carrying local call numbers or availability information, and cannot be used to give information about number of copies held, or details of serial holdings.
The MARC holdings format specifies a number of fields to contain holdings information. The 852 field can be used to give information about the location of a single copy (or multiple copies shelved together) of an item at a single location. It can be used to carry a summary description of holdings for each copy. The 852 field is one of those that may also be embedded in a bibliographic record, and repeats of the field can be used to give information about copies at multiple locations.
The greatest amount of detail is provided by the use of multiple related fields in the ranges 853-855, 863-866, 873-876. Multiple instances of these fields are intended to be used to describe in detail holdings of a single copy of an item, and therefore relate to a single instance of an 852 field. Each grouping of an 852 and multiple related 853-876 fields can be seen as a holdings subrecord. However, US- and CanMARC do not support subrecords, so the holdings format explicitly permits only a single grouping of 852 + 853-876 to be embedded in a bibliographic record. (it should be noted that other MARC formats, notably UNIMARC, do support subrecords). The MARC Manuals therefore specify that only a single "cluster" of 852 with multiple detailed holdings fields may be embedded in a MARC record. Otherwise, the holding must be handled as separate holdings records.
The most detailed holdings for other than a single copy can therefore be transferred only as a cluster of records: a MARC bibliographic record plus multiple linked MARC holdings records. Unfortunately, Z39.50 cannot directly return a cluster of separate records: if a search on a bibliographic access point retrieves 10 records, then only 10 records can be returned, not 10 bibliographic records, plus a cluster of 5 additional holdings records associated with each bibliographic record.
A number of systems have avoided the problem by delivering holdings information, whether for a single catalogue or for a union catalogue, in server defined fields of a MARC bibliographic record. Both RLIN and OCLC have taken this approach. This, however, requires union catalogue participants to be aware of field definitions that are meaningful to a single (vendor's) system, and requires additional development effort on the part of the client implementor for each server that is accessed. It therefore impedes interoperability and encourages multiple incompatible closed groups of union catalogue systems.
In an attempt to overcome this problem, in July 1995 the National Library of Canada proposed, for its Virtual Canadian Union Catalogue project, a mechanism that could be used to support multiple holdings subrecords within a MARC bibliographic record. This involved the addition of a $9 subfield to explicitly link details fields with the 852 describing the copy. This solution is however not fully satisfactory since it introduces a private extension to the semantics of the existing MARC formats, one that a number of vendors are unable or unwilling to support.
A third approach is to use multiple searches to implement the functionality of the union catalogue. In this approach a first search would be carried out to retrieve bibliographic records, which would presumably be delivered as MARC bibliographic records. These might return locations in field 850 and copy information in repeats of 852. Subsequently, additional searches would be carried out to retrieve detailed holdings information for specific items discovered in the bibliographic search. The search for detailed holdings might be directed to a different server, such as the system indicated by the location obtained from a union catalogue. The detailed holdings can be returned in the form of MARC holdings records, and this approach therefore offers the potential of an entirely MARC-based solution. Unfortunately, very few vendors have indicated their intention to implement support for the MARC holdings format, so the level of interest in this approach is likely to be low.
An alternative approach wrap clusters of bibliographic and holdings records inside a different syntax that acts as a wrapper to hold multiple records. The OPAC record defined in the 1995 Z39.50 standard is a candidate for such a wrapper record. The OPAC record has an additional advantage in that it permits the transfer of circulation status information. This information cannot be carried in a MARC bibliographic or holdings record by itself.
Use of the OPAC record, however, requires some agreement among the parties cooperating to implement the distributed union catalogue. The record provides a choice of two mechanisms for including holdings information: MARC holdings records, or the HoldingsAndCircData data type defined for the record. It seems unreasonable to expect the implementors to have to support both of these forms of carrying holdings information. Only one of these choices may be present for each holding, and neither the MARC bibliographic nor holdings record carries circulation information. The HoldingsAndCircData subrecord, however, does not provide the same level of granularity of information as does the MARC holdings record, so there are trade-offs. It should also be noted that the OPAC record was designed to carry the information required to construct displays to be used by patrons of a single library. It does not, therefore, carry some information that is essential for union catalogue and interlending purposes, such as the library's lending policy for an item.
This section describes some of the issues that must be addressed by a profile for transferring holdings information via Z39.50.
Z39.50 is coming to be seen as a vital tool in enabling libraries and their patrons to cope with the increasing importance of resource sharing in libraries and the increasingly heterogeneous computing environment in which they operate. If Z39.50 is to be used effectively for resource sharing, implementors, and particularly library system vendors must begin to support agreed-on mechanisms transferring locations, holdings and circulation information in a standardized way. If the virtual library is ever to become a reality, real interoperability between library systems via Z39.50 is an essential precondition.
In order to achieve interoperability, the issues described in this paper need to be resolved by consensus, and all the parties concerned need to agree to undertake any implementation effort required within a reasonable timeframe.
RecordSyntax-opac {Z39-50-recordSyntax opac(102)} DEFINTIONS ::=
BEGIN
IMPORTS InternationalString FROM Z39-50-APDU-1995;
OPACRecord ::= SEQUENCE {
bibliographicRecord [1] IMPLICIT EXTERNAL OPTIONAL,
holdingsData [2] IMPLICIT SEQUENCE OF HoldingsRecord OPTIONAL
}
HoldingsRecord ::= CHOICE {
marcHoldingsRecord [1] IMPLICIT EXTERNAL,
holdingsAndCirc [2] IMPLICIT HoldingsAndCircData
}
HoldingsAndCircData ::= SEQUENCE {
-- the following elements are required to display holdings in conformance with NISO standards.
typeOfRecord [1] IMPLICIT InternationalString OPTIONAL, -- LDR 06
encodingLevel [2] IMPLICIT InternationalString OPTIONAL, -- LDR 17
format [3] IMPLICIT InternationalString OPTIONAL, -- 007 00-01
receiptAcqStatus [4] IMPLICIT InternationalString OPTIONAL, -- 008 06
generalRetention [5] IMPLICIT InternationalString OPTIONAL, -- 008 12
completeness [6] IMPLICIT InternationalString OPTIONAL, -- 008 16
dateOfRecord [7] IMPLICIT InternationalString OPTIONAL, -- 008 26-31
nucCode [8] IMPLICIT InternationalString OPTIONAL, -- 852 $a
localLocation [9] IMPLICIT InternationalString OPTIONAL, -- 852 $b
shelvingLocation [10] IMPLICIT InternationalString OPTIONAL, -- 852 $c
callNumber [11] IMPLICIT InternationalString OPTIONAL, -- 852 $h and $i
shelvingData [12] IMPLICIT InternationalString OPTIONAL, -- 852 $j thru $m
copyNumber [13] IMPLICIT InternationalString OPTIONAL, -- 852 $t
publicNote [14] IMPLICIT InternationalString OPTIONAL, -- 852 $z
reproductionNote [15] IMPLICIT InternationalString OPTIONAL, -- 843
termsUseRepro [16] IMPLICIT InternationalString OPTIONAL, -- 845
enumAndChron [17] IMPLICIT InternationalString OPTIONAL, -- all 85x, 86x
volumes [18] IMPLICIT SEQUENCE OF Volume OPTIONAL,
-- repeats for each volume held
circulationData [19] IMPLICIT SEQUENCE OF CircRecord OPTIONAL
-- repeats for each circulating item.
}
Volume ::= SEQUENCE {
enumeration [1] IMPLICIT IntenationalSting OPTIONAL,
chronology [2] IMPLICIT InternationalString OPTIONAL,
enumAndChron [3] IMPLICIT InternationalString OPTIONAL
}
CircRecord ::= SEQUENCE {
availableNow [1] IMPLICIT BOOLEAN,
availabilityDate [2] IMPLICIT InternationalString OPTIONAL,
availableThru [3] IMPLICIT InternationalString OPTIONAL,
restrictions [4] IMPLICIT InternationalString OPTIONAL,
itemId [5] IMPLICIT InternationalString OPTIONAL,
renewable [6] IMPLICIT BOOLEAN,
onHold [7] IMPLICIT BOOLEAN,
enumAndChron [8] IMPLICIT InternationalString OPTIONAL,
midspine [9] IMPLICIT InternationalString OPTIONAL,
temporaryLocation [10] IMPLICIT InternationalString OPTIONAL
}
Leader/06 - Type of record: v multipart item holdings x single-part item holdings y serial item holdings Leader/17 - Encoding level 1 holdings level 1 2 holdings level 2 3 holdings level 3 4 holdings level 4 5 holdings level 4 with piece designation m mixed levels z other level 001 Control number 004 Control number of related bibliographic record 005 Date/time of latest transaction 007 Physical description fixed field 008 Fixed-length data elements /00-05 - Date entered on file /06 - Receipt or acquistion status 0 unknown 1 other receipt or acquisition status 2 completed 3 on order 4 currently received 5 not currently received /07 - Method of acquisition d deposit e exchange f free g gift p purchase z other u unknown /08-11 - Intent to cancel date /12 - General retention policy 0 unknown 1 other 2 retained except as replaced by updates 3 sample issue retained 4 retained until replaced by microform 5 retained until replaced by cumulation [etc.] 6 retained for a limited period 7 not retained 8 permanently retained /13-15 - Specific retention policy /16 - Completeness 0 other 1 complete 2 incomplete 3 scattered 4 not applicable /17-19 - Number of copies reported /20 - Lending policy a will lend b will not lend u unknown /21 - Reproduction policy a will reproduce b will not reproduce c unknown /22-24 - Language [of holdings statement] /25 - Separate or composite copy report 0 separate copy report 1 composite copy report /26-31 - Date of report 010 Library of Congress Control Number [for bibliographic item] 014 Linkage number 020 ISBN 022 ISSN 023 Standard Film Number 024 Standard Recording Number 027 Standard Technical Report Number 030 CODEN Designation 035 System Control Number 583 Action Note 841 Holdings Coded Data Values - contains coded data from the leader and 008 when a holdings record is embedded in a bibliographic record 842 Textual Physical Form Designator 843 Reproduction Note 844 Name of Unit 845 Terms Covering Use and Reproduction Note 852 Location $a - location $b - sublocation or collection $c - shelving location $e - address $f - coded location qualifier $g - non-coded location qualifier $h - classification part [of call number] $i - item part [of call number] $j - shelving control number $k - call number prefix $l - shelving form of title $m - call number suffix $n - country code $p - piece designation $q - piece physical condition $s - copyright article-fee code $t - copy number $x - nonpublic note $z - public note $2 - source of classification or shelving scheme $3 - materials specified $8 - link and sequence number 853 Captions and Pattern - Basic Bibliographic Unit $a - first level of enumeration $b - second level of enumeration $c - third level of enumeration $d - fourth level of enumeration $e - fifth level of enumeration $f - sixth level of enumeration $g - alternative numbering scheme, first level of enumeration $h - alternative numbering scheme, second level of enumeration $i - first level of chronology $j - second level of chronology $k - third level of chronology $l - fourth level of chronology $m - alternative numbering scheme, chronology $t - copy $u - bibliographic units per next higher level $v - numbering continuity $w - frequency $x - calendar change $y - regularity pattern $3 - materials specified $8 - link and sequence number 854 Captions and Pattern - Supplementary Material
subfields as 853 plus $o - type of supplementary material 855 Captions and Pattern - Indexes
subfields as 853 plus $o - type of index 856 Electronic Location and Access $a - host name $b - IP address $c - compression information $d - path $f - electronic name $g - electronic name - end of range $h - processor of request $i - instruction $j - bits per second $k - password $l - logon/login $m - contact for access assistance $n - name of location of host in subfield $a $o - operating system $p - port $q - file transfer mode $r - settings $s - file size $t - terminal emulation $u - URL $v - hours access method available $w - record control number $x - nonpublic note $z - public note $2 - access method $3 - materials specified 863 Enumeration and Chronology -Basic Bibliographic Unit [requires 853 to generate a display] $a - first level of enumeration $b - second level of enumeration $c - third level of enumeration $d - fourth level of enumeration $e - fifth level of enumeration $f - sixth level of enumeration $g - alternative numbering scheme, first level of enumeration $h - alternative numbering scheme, second level of enumeration $i - first level of chronology $j - second level of chronology $k - third level of chronology $l - fourth level of chronology $m - alternative numbering scheme, chronology $n - converted Gregorian year $p - piece designation $q - piece physical condition $s - copyright article-fee code $t - copy number $w - break indicator $x - nonpublic note $z - public note $8 - link and sequence number 864 Enumeration and Chronology - Supplementary Material [requires 854 to generate a display] subfields as 863 plus $o - title of supplementary material 865 Enumeration and Chronology - Indexes [requires 855 to generate a display]
subfields as 863 plus $o - title of index 866 Textual Holdings - Basic Bibliographic Unit $a - textual string $x - nonpublic note $z - public note $8 - link and sequence number 867 Textual Holdings - Supplementary Material - subfields as 866 868 Textual Holdings -Iindexes - subfields as 866 876 Item Information - Basic Bibliographic Unit $a - internal item number $b - invalid or cancelled internal item number $c - cost $d - date acquired $e - source of acquisition $h - use restrictions $j - item status $l - temporary location $p - piece designation $r - invalid or cancelled piece designation $t - copy number $x - nonpublic note $z - public note $3 - material specified $8 - link and sequence number 877 Item Information - Supplementary Material
subfields as 876 878 Item Information - Indexes
subfields as 876