Access Control, Account, Browse and Sort

The Access control, Accounting, Browse and Sort facilities provide the next level of services for Z39.50 beyond the basic search and retrieve.

Contents Map: Z39.50 Part 2

Contents: this page

Access Control, Accounting/Resource Control, Browse, Sort

Access Control

Access control has far reaching implications for the services that libraries might wish to operate via Z39.50.  There have been debates about what should be allowed to happen over a Z39.50 session - should libraries download MARC records or not - who has copyright?  The Access control built into Z39.50 allows the Z-server (target) to disallow virtually any operation that might be asked of it by the Z-client (origin).  If access control fails, then the Z-Association can either continue with those operations that it is allowed to use or terminate. An access control “challenge” can be made in respect of individual records if desired. Thus a library might want certain records only to be provided on a paid for basis or, for security reasons, not to be viewed without authorisation.

The format of the messages is defined in the standard or can be agreed separately by libraries and information resources.

This service is initiated by the Z-server (target) as part of a specific operation or the whole Z-association. It can optionally include a resource report which could say how current or predicted expenditure was looking and whether it would exceed agreed limits. Consent to continue an operation can be sought from the Z-client - “can I spend some more of your money?”

Resource Control

This service is initiated by the Z-server (target) as part of a specific operation or the whole Z-association. It can optionally include a resource report which could say how current or predicted expenditure was looking and whether it would exceed agreed limits.  Consent to continue an operation can be sought from the Z-client - “can I spend some more of your money?”

Trigger Resource Control

This service is triggered by the Z-client (origin) and basically asks the Z-server (target) “how much is there left in the account?”  The response is a resource control message with a resource report. 

Resource Report

The resource report which is passed to the Z-client (origin) can contain a lot of detailed information including figures on:

• Numbers of records in current set so far
• Estimated complete set size
• Processing time so far and estimated
• Cost so far for this operation
• Estimated cost if completed
• Cost for the Z-Association

Summary

Thus the Z-client can ask the Z-server “how much is this costing me?” to which a response might be $300 - do you want me to continue? The Z-Association can set, at the Initialisation stage, how resource control should be used. Typically, the Z-client (origin) might always have to respond with a “Yes” to a “Continue?” from the Z-server (target).

The sort facility is a single service of Sort carried out on the Z-server (target).  Some Z-clients have sorting built in so that they can sort (and filter) the results once they have the records retrieved. This way of working is easier, faster and more flexible. Currently not many Z-servers have the sort facility operational so it is the sensible way to approach this function.  It is also the most efficient way to handle the vagaries of international sorting sequences since different languages sort in different orders.

The standard defines parameters for the naming of the sorted result set, the sort sequence and statuses to say whether they have been successfully completed or not.

Browse (Scan)

Browse is another facility that is not currently (early 1998) supported on many Z-servers. The single service is called Scan and allows an ordered list e.g. alphabetical list of subject headings or authors to be scanned or browsed.  This is in contrast to a typical Z39.50 search and retrieve where a Result-Set of records is retrieved in response to a query. Scan is a request to bring back a list of headings in order from a specific start point and allow browsing.  Browsing is an important part of research and the adoption and improvement of this feature will provide much improved features when searching remote catalogues.

The Scan request is issued from the Z-client (origin) much as a Query is issued. The parameter list shows the controls that can be set for a scan operation.  A good Z-Client can also use the returned information as a specific Query without re-entry so that on selection of a personal author for example, the user can then request books by that author.