Handling Bibliographic Holdings Information in Z39.50:
Implications for the Z Texas Profile

by

William E. Moen, Ph.D.
wemoen@jove.acs.unt.edu
School of Library and Information Sciences
University of North Texas
Denton, TX 76203

Z39.50
Home | Implementation Resources

Contents
1.0    Introduction
2.0    Background
3.0    Problems in Accessing and Retrieving Holdings Information
4.0    The OPAC/Holdings Schema Explained
5.0    The Use of the OPAC/Holdings Schema in the Z Texas Profile
6.0    Conclusion
References
Appendix A: Selected Definitions of OPAC/Holdings Schema Elements

1.0    Introduction

The ANSI/NSIO Z39.50 standard has the positive potential to affect libraries' abilities to share resources.  An early use of Z39.50 was to identify bibliographic records for copy cataloging purposes.  Librarians realized, however, that Z39.50 could enhance service to users by providing information about who owned copies of the resources described by the bibliographic records and any constraints on borrowing those items.   Holdings information is critical to several library applications, especially interlibrary loan and union catalogs.  Recently the Z39.50 Implementors Group (ZIG) has addressed the issues related to exchanging holdings information through Z39.50.   Agreements at the past several ZIG meetings has put in place the mechanism for standardizing the retrieval of holdings information.  The timing is excellent for the Z Texas Project since we can use the standard mechanism and specify its use in the Z Texas Profile.   This paper describes this mechanism and proposes how the Z Texas Profile can specify its use.

2.0    Background

The evolution of Z39.50 has addressed increasingly sophisticated requirements of the library community.  The initial work on Z39.50 in the 1980s focused on search and retrieval of bibliographic records (usually some variant of the MARC record) to assist library cataloging functions. In fact, the earliest application of the Z39.50 protocol was to support the identification and interchange of name authority records.  Since that time, librarians and other groups have identified important functional requirements for Z39.50, and over time the standard has evolved to address these requirements. 

A key requirement for library resource sharing involves the use of bibliographic holdings information.  The Z39.50 standards developers provided one approach to retrieving holdings and circulation information by defining a Z39.50 OPAC Record Syntax in Z39.50-1995.   This approach was limited by they ways in which local systems processed and stored holdings information.  There was also a limit in the extent of holdings that could be contained in a Z39.50 OPAC Record.

Holdings information is critical in another important area: virtual union catalog applications.  The National Library of Canada and other have experimented and deployed Z39.50 to simulate a union catalog. Part of this project included the evaluation of Z39.50 usefulness in creating a virtual union catalog.  An important result of that project was the realization that library automation systems handle and process bibliographic holdings information in various ways . The lack of cross-system consistency in handling holdings information focused renewed attention on solving the Z39.50 holdings information problem.

Participants in the various union catalog projects and other applications wanting to use Z39.50 to access and retrieve holdings information began work in 1997 on a standards-based approach to solving the holdings information problems.  The result of this effort is currently reaching stability with the release of the OPAC/Holdings Schema: Definitions and Examples (Third Draft -- March 10, 1999).   At the most recent ZIG meeting in Palo Alto, California (March 17-19), participants approved, with minor changes, the latest draft of the OPAC/Holdings Schema.  It is now ready for use by Z39.50 implementors.

3.0    Problems in Accessing and Retrieving Holdings Information

The need for bibliographic holdings information, especially in applications of virtual union catalogs, is critical.  When users (librarian or patron) know a specific item they are interested in acquiring,  they search a union catalog with the goal of retrieving  location and availability information rather than the bibliographic information about the item.  Zeeman and Turner (1997) describe some of the basic problems related to interchanging holdings information.  Transferring holdings information is problematic since holdings information may be embedded in a USMARC bibliographic record (i.e. in several of the 85x fields) or may be held in separate holdings records that can be expressed in the USMARC Holdings Format.  The USMARC Holdings records are capable of carrying much more detailed holdings information than is possible by embedding holdings information in a USMARC bibliographic record.

Embedding holdings information in the bibliographic record's 850 field allows the identification of institutions that hold the item, but other pertinent information such as local call numbers, availability information, information about the number of copies, or details of serial holdings cannot be carried in the bibliographic record.  For greater detail, the USMARC Holdings Format needs to be used, and often there will be multiple holdings records linked to a single bibliographic record.  "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" (Zeeman and Turner, 1997).   But there are a limited number of vendors that do or plan to support the MARC holdings format in their implementations.

The diversity of detail of holdings information, the various ways the information an be carried in MARC records, and the differences in how library systems implementors process the holdings information (i.e., store, retrieve, and express) has led to major challenges for designers and builders of virtual union catalogs.  The experience of the vCuc Project demonstrated that "there are no common ways, at this time, to retrieve consistent holdings information using the Z39.50 protocol, due to the fact that most implementors have adopted a more or less proprietary approach in retrieving this information" (St-Gelais & Data Research Associates, 1997, p. 2).

In part, the difficulty of using Z39.50 to retrieve holdings information is a problem because of the constraints of the underlying model of Z39.50.  This model simply is that a Z-client passes a query to a Z-server that executes it on a local database.   The Z-server compiles a result set that consists of the records in the database that meet the query criteria.  The Z-client can then ask for one or more records from the result set.  If there is a cluster of holdings records associated with one of the bibliographic records in the result set, the Z39.50 protocol doesn't offer a way for the Z-client to request or the Z-server to return them from the initial result set.  Several project and systems have attempted to solve this and other holdings information problems by implementing proprietary solutions, but this has simply compounded the problem since there is no standards-based approach that might provide consistency in transferring holdings information.

The approach in Z39.50-1995 defined an OPAC Record Syntax that could be used to wrap clusters of bibliographic and holdings information together for transfer to the Z-client.  This solution was problematic because the OPAC Record Syntax allowed either the transfer of MARC Holdings records within it or the compilation of holdings and circulation data.  Options such as this make interoperability more difficult.  Further, the OPAC Record Syntax was oriented to transferring holdings and circulation data for a single library and thus did not accommodate needs for a virtual union catalog. 

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4.0    The OPAC/Holdings Schema Explained

The origins of the current OPAC/Holdings Schema date from 1997 when Data Research Associates (DRA) under the authorship of Rolande St-Gelais issued Holdings Retrieval using GRS-1 and OPAC for discussion at the August 1997 ZIG meeting. Based on discussions at that meeting, St. Gelais worked with a subgroup of ZIG members developed a proposal for an OPAC/Holdings Schema that would address the problems outlined above.  An early controversial decision was to use the Z39.50 Generic Record Syntax (GRS-1) to retrieve and package up holdings information as specified in the OPAC/Holdings Schema. 

St-Gelais' paper included Table 1 (below) that details a set of objectives related to retrieving holdings information.  Some of the objectives were considered "fundamental" (objectives 1-4), "quite important" (objectives 5-6), "if possible" (objectives 7-8), and "nice to" (objectives 9-10).   Any solutions developed needed to address these objectives:

Table 1
Objectives and Purposes of Holdings Information Exchanged through Z39.50

Taking account of the challenges in achieving these objectives, St-Gelais also identified a set of criteria to consider when evaluating the proposed solutions:

• Respect the Z39.50 result set model, i.e., one retrieval record is to be returned per result set item
• Version 2 compatible
• Performance versus holdings information needed
• Common holdings data vehicle
• Independence between bibliographic and holdings data vehicles
• No prior knowledge of a specific server's database model.

Since the early discussion papers and proposals, work continued on an OPAC/Holdings Schema, and this Schema was approved by the ZIG at the March 1999 meeting in Palo Alto, CA.

The Schema describes a model of a bibliographic item that is accommodated by the Schema.  The Schema defines an OPAC/Holdings record constituted by the schema as carrying both bibliographic information about an item along with holdings information associated with the item. The Schema document adopts fundamental definitions for a bibliographic item and bibliographic unit from ISO 10324.  (See Appendix A for definitions to assist in understanding this explanation of the OPAC/Holdings Schema.) 

The Schema views a bibliographic unit as comprising any number of parts that may be issued over time.  It defines three levels at which holdings information may be associated with a bibliographic item (paraphrased from the Schema document):

• Bibliographic Level: holdings data for a bibliographic item in a generic way, i.e., independently of any specific copy.
• Copy Level: holdings data for each individual copy of a bibliographic item
• Piece Level: circulation data for the different physical units associated with a bibliographic item

Associated with these levels are three holdings reporting levels that correspond with the levels described previously:

• Bibliographic Level Holdings
• Copy Level Holdings
• Piece Level Holdings

For each reporting level, the Schema offer several associated levels of data as follows:

• Bibliographic Level Holdings
  • Level B-1: Minimal bibliographic level holdings (i.e., "Location only")
  • Level B-2: Summary bibliographic level holdings (i.e., non copy-specific summary holdings)
  • Level B-3: Detailed bibliographic level holdings (i.e., non copy-specific detailed holdings)
• Copy Level Holdings
  • Level C-1: Minimal copy level holdings (i.e., "Copies only")
  • Level C-2: Summary copy level holdings (i.e., summary holdings per copy)
  • Level C-3: Detailed copy level holdings (i.e., detailed holdings per copy)
  • Level C-4: Extended copy level holdings (i.e., detailed holdings with circulation information)
• Piece Level Holdings
  • Level P-1: Minimal piece level holdings (i.e., circulating pieces only)
  • Level P-2: Summary piece level holdings (i.e., summary content of circulating pieces)
  • Level P-3: Detailed piece level holdings (i.e., detailed content of circulating pieces)

The Schema defines the elements associated with holdings data for the three reporting levels and the levels of data included at each level.  In addition, the Schema indicates the USMARC Authority Format fields and subfields associated with selected elements.

The use of schemas in Z39.50 provides a vocabulary and language shared by both the Z-client and Z-server for purposes of communication.  In the case of the OPAC/Holding Schema, the schema elements provide labels to identify discrete units of holdings information.  For example, the OPAC/Holding Schema element locationName will be associated with the following information: "name of the physical site, i.e., name of institution followed, optionally, by the name(s) of one or many of its sub-divisions."  Thus, for each schema element, exact definitions and descriptions of the data to be associated with the element are provided (see Appendix A).

The Schema in its final form will provide an OPAC/Holdings Tagset that will assign a number to each of the elements in the schema. In addition, the Schema provides an Abstract Record Structure that shows the relationship between the elements of defined by the Schema, especially the hierarchical relationships where one schema element is a subelement to another element.

In summary, the OPAC/Holdings Schema provides a fully detailed structure in which Z39.50 implementors can map local holdings information where each unit of holdings information is explicitly labeled.  Upon retrieval by the Z-client of an OPAC-1 record, the Z-client will be able to process the information in a meaningful manner.  The OPAC/Holdings Schema makes no assumptions nor prescribes how local systems store or process their local holdings information.  The local server is free to utilize existing USMARC Holdings Format records, assemble the holdings information at the time of retrieval, etc.   Local server implementors need only map their holdings information to the elements of the OPAC/Holdings Schema.  Once the OPAC-1 Record is assembled by the Z-server, the Generic Record Syntax (GRS-1) provides the syntax to package the elements for transfer to the Z-client. 

Because of the various levels of reporting that are offered and the likelihood that a single bibliographic item may be available in  multiple copies and locations, the OPAC/Holdings Schema's Abstract Record Structure indicates for each of the reporting levels the elements that are mandatory, optional, and repeatable.  In addition, to make the OPAC/Holdings Schema usable by Version 2 Z-clients and Z-servers, the final version of the Schema will define a set of static element set names (ESNs) that group selected sets of elements for retrieval in an OPAC-1 record. These ESNs will likely correspond to the 10 reporting levels listed above (see discussion below in 5.0 Use of OPAC in the Z Texas Profile).  Z-clients and Z-servers supporting Version 3 may use the comp-Spec parameter of the Present Service to specify the desired composition of elements for the retrieval record.  The latter approach provides the potential for further customization of the composition of the retrieval record.

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5.0 The Use of the OPAC/Holdings Schema in the Z Texas Profile

At the February 1999 meeting of the Z39.50 Texas Implementors Group (TZIG), the participants agreed that Release 1.0 of the Z Texas Profile would include the specifications for using the OPAC/Holdings Schema.  Participants agreed that access to holdings information was a fundamental requirement, especially as the Z Texas Profile is attempting to lay the technical infrastructure for state-wide resource sharing.   This section proposes how the OPAC/Holdings Schema may be specified in the Profile.

A key decision for the Profile is to determine the level of reporting of holdings information that is necessary, at least in the short -term to gain experience with the OPAC/Holdings Schema.   Section 4.0 identified the various levels of reporting, and for Release 1.0 of the Z Texas Profile, the following reporting levels are proposed as indicated by bold:

• Bibliographic Level Holdings
  • Level B-1: Minimal bibliographic level holdings (i.e., "Location only")
  • Level B-2: Summary bibliographic level holdings (i.e., non copy-specific summary holdings)
  • Level B-3: Detailed bibliographic level holdings (i.e., non copy-specific detailed holdings)
• Copy Level Holdings
  • Level C-1: Minimal copy level holdings (i.e., "Copies only")
  • Level C-2: Summary copy level holdings (i.e., summary holdings per copy)
  • Level C-3: Detailed copy level holdings (i.e., detailed holdings per copy)
  • Level C-4: Extended copy level holdings (i.e., detailed holdings with circulation information)
• Piece Level Holdings
  • Level P-1: Minimal piece level holdings (i.e., circulating pieces only)
  • Level P-2: Summary piece level holdings (i.e., summary content of circulating pieces)
  • Level P-3: Detailed piece level holdings (i.e., detailed content of circulating pieces)

Each of these levels of reporting will be assigned an Element Set Name (ESN), and the Z-client will use the ESN to request the holdings information at a single reporting level.  The Z-client may use successive Presents using different ESNs to retrieve additional holdings information.

The following describes the OPAC/Holdings Schema elements that would be associated for each ESN (note that the names used in the ESN's listed below may be changed when the official ESNs are assigned by the OPAC/Holdings working group).  Readers should refer to the OPAC/Holdings Scheme for additional details.  The first instance of an element in the tables is linked to its definition in Appendix A.

Level B-1: Minimal bibliographic level holdings (i.e., "Location only")
ESN: MinimalBibliographicLevelHoldings
Description: Provides list of sites that have holdings of the bibliographic item 

Level B-2: Summary bibliographic level holdings (i.e., non copy-specific summary holdings)
ESN: SummaryBibliographicLevelHoldings
Description: Reports summary holdings information about the bibliographic item, and not copy-level information

Level C-1: Minimal copy level holdings (i.e., "Copies only")
ESN:MinimalCopyLevelHoldings
Description: Reports the specific location of each (full or partial) copy of a bibliographic item held by a site

Level C-2: Summary copy level holdings (i.e., summary holdings per copy)
ESN: SummaryCopyLevelHoldings
Description: Reports summary holdings for each copy held by a site

Level C-4: Extended copy level holdings (i.e., detailed holdings with circulation information)
ESN: Extended CopyLevelHoldings
Description: Reports detailed holdings for each copy along with circulation information on the copy held by a site

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6.0    Conclusion

Z39.50 now has a mechanism in the OPAC/Holdings Schema to standardize the retrieval of holdings information across multiple databases.  While it allows Version 2 Z-clients and Z-servers to use this Schema, it does raise the requirement that they must support GRS-1.  The Z Texas Profile, in its attempt to lay a technical foundation for statewide information sharing, will break new ground by profiling the use of the OPAC/Holding Schema.  It is a wise decision and may lead to an appreciation of Z39.50 utility within the state's library community.

References

International Organization for Standardization.  (1997).  ISO 10324: Information and documentation -- Holdings statements -- Summary level.

St-Gelais, Rolande.  (1999, March 10). OPAC/Holdings schema: Definitions and Examples. Third draft -- March 10, 1999).  Available: <http://www.collectionscanada.ca/iso/z3950/archives/holds7.htm>.

St-Gelais, Rolande & Data Research Associates, Inc. (1997, August 15).  DRA information: Holdings retrieval using GRS-1 and OPAC.  St. Louis, MO: Data Research Associates. 

Zeeman, Johan & Turner, Fay. (1997, April 2).  Use of Z39.50 to access distributed union catalogues: Discussion paper. Available: <http://www.collectionscanada.ca/iso/z3950/archives/holds.htm>.

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Appendix A
Selected Definitions of OPAC/Holdings Schema Elements

The following extracts from St-Gelais, Rolande a selected set of elements for which definitions are provided. These elements correspond to the elements required in the several Element Set Names (and associated reporting levels) proposed for use in the Z Texas Profile.  For a complete list of elements, their definitions, and the controlled values for some of the elements, please see the original document.

copyLocation:

This element provides the physical location of a full or partial copy of the bib item within a site. (The location therefore indicates where a certain number of parts (physical units) of a specific copy reside and where this portion may be found).