Document Requesting with Z39.50
Contribution to eLib Study on Document Requesting Standards

Denis Lynch, SilverPlatter Information Ltd. 
DenisL@SilverPlatter.com

1.	Contents
1. Contents	
2. Introduction	
2.1. Z39.50 Core Operation	
2.2. Extended Services	
2.3. Standard Development	
2.4. Implementation Status	
3. Item Order in Z39.50	
3.1. Operation	
3.2. Standard Development	
3.3. Implementation Status	

2.	Introduction
The Z39.50 Search and Retrieval protocol is an American National Standard that has been adopted as an ISO standard and is in wide use in the library community. Z39.50’s wide use to access bibliographies (library catalogues and abstract & index databases) leads naturally to inclusion of facilities for requesting delivery of items.
This section describes Z39.50 sufficiently to understand the operation of the item order service. The following section describes the item order service itself.
2.1.	Z39.50 Core Operation
The fundamental Z39.50 services are “Init” (login), “Search” and “Present” (retrieval). These services are built on a well articulated model, summarised in Figure 1. Additional services provide capabilities that are common in information retrieval systems, notably “Scan” (index browse) and result set “Sort”. There are several important aspects of the model:
•	Only services directly relevant to information retrieval are included.
•	All operations produce results that exist only within the context of a single session.
•	The model is independent of any underlying implementation. Most Z39.50 servers act as front ends to search engines that were developed independently.
•	The standard query (the “type 1” or “RPN” query) is also defined in a purely logical way, independent of any specific database organization.

Figure 1

2.2.	Extended Services
Practical information systems - from integrated library systems to commercial online services - provide services that go well beyond information retrieval. The most common such services are
•	Saved result sets
•	Periodic queries (also known as SDI) 
•	Document delivery (also interlibrary loan or item order)
•	Record export
These services involve operations that extend beyond a single session. The Z39.50 protocol makes provision for these non-core services with a single service called “Extended Services.” The operation of an Extended Service is basically:
•	The client builds a “parameter package” with the information the server needs for the specific service.
•	The client inserts the parameter package into an Extended Services “Create” request, and sends the request to the server.
•	The server validates the request and processes it in any appropriate way. This will usually involve an offline process of some kind.
•	The server responds to the client indicating that the request has been accepted.
•	At a later time, perhaps in an entirely different session, a client can use standard Search and Present operations directed at the Extended Services database (“IR-Extend-1”) to monitor the progress of the operation.
•	Other Extended Services requests can “Delete” or “Modify” an Extended Services package retained by the server.
	It should be noted that the Extended Services operations and database can be implemented in any way that is appropriate for the situation. In particular the Extended Services database need not literally exist at the server.
	There are many details omitted from this description. The description should be sufficient to set the stage for a description of the Item Order service.
2.3.	Standard Development
The Z39.50 protocol - and the related Extended Services parameter packages - are maintained by the Z39.50 Implementor’s Group (ZIG). The ZIG is chartered by the American National Standards Institute’s National Information Standards Organization. Membership in the ZIG is international and open to all interested parties. Over the past several years the biannual meetings have alternated between locations in the United States and Europe. Much of the business of the ZIG is carried out on its mailing list (Z3950IW). Subscriptions are arranged by mailing the list server at LISTSERV@nervm.nerdc.ufl.edu.
2.4.	Implementation Status
The core of Z39.50 is widely implemented. Nearly all integrated library systems include a Z39.50 server that provides access to the catalogue; many library systems also include a Z39.50 client to incorporate reference data sources. Many large union catalogue systems are accessible by Z39.50, as well as important reference databases supplied by OCLC, Ovid and SilverPlatter for example.
3.	Item Order in Z39.50
Z39.50’s Extended Services provide a natural framework for an item request service. The Item Order request makes explicit provision for using the ILL Request PDU to package the information required to fully specify an item order request. The expectation is that the ILL standard reflects a sufficient range of requirements for a wide range of applications, and that the ILL standard will be updated as new applications arise.
3.1.	Operation
The Item Order extended service is envisioned to be used in a situation where a true ILL system, or an alternative document delivery system, is available to the Z39.50 server. Relevant Extended Services requests are translated into commands appropriate to the specific ILL system. The ILL system will be the participant in all ILL protocol exchanges. Z39.50 clients can only interrogate the status of an active request, or possibly delete or modify the request.

The system environment is show in Figure 2.

Figure 2
An Item Order request will normally be sent after the desired item has been identified in a result set. The Item Order request makes explicit provision for identifying the requested item by a position within a result set. In this case the item information in the ILL Request PDU isn’t used. It is also likely that the system will have much of the user’s identification as a result of the login authentication process. To support requests that omit these items a Z39.50 version of the ILL Request PDU has been defined that has all data items optional.
3.2.	Standard Development
The Z39.50 Item Order usage of the ILL Request Protocol Data Unit was developed and is now maintained by the National Library of Canada, which is also the maintenance agency for the ILL standard itself. Information related to ILL and Z39.50 Item Order can be found at http://www.nlc-bnc.ca/ifla/II/illprot.htm.
3.3.	Implementation Status
The Item Order service is implemented in at least two American systems. OCLC’s First Search accepts Item Order with the ILL Request PDU. The request is forwarded to OCLC’s ILL system.  The AT&T Library system has an experimental implementation of Item Order that is available for interoperability testing.
Indications are that more implementations will follow.