Z39.50 Record Source Schema

Revised Draft For Review

August 23, 2000

This schema definition was approved at the July ZIG meeting, subject to the following change: the url for a source record need not necessarily be a Z39.50 url; multiple urls may be supplied (actually, URIs), in the case where multiple URIs (possibly of different types) exist for the record.

The definition has been revised, for review. Please consider the following question. Suppose two or more URIs are supplied by a surrogate record. Should the client assume that they all identify the same source record (i.e. at the same server)? Or, should it be possible for the intermediary, having decided that two or more records on different source servers are duplicates, to supply, within a single surrogate record, URIs to these multiple records? If this is allowed though, then how would the client be able to distinguish these two cases, that is, whether two URIs identify the same source record (at the same server) or duplicate records at different servers?

The Object Identifier for this Schema definition is 1.2.840.10003.13.11

Background

This schema is defined in response to a requirement to identify the "source" of a Z39.50 record. The requirement is for a Z39.50 server, acting as an intermediary, to provide information to the client for a given result set record, enabling the client to subsequently retrieve the record directly from the source server for that record.

Model

In the model for this schema, the Z39.50 server acts as an intermediary, receiving queries against a "virtual" database and retransmiting the queries to a set of other Z39.50 servers. The intermediary server creates a single logical result set combining the results from the individual result sets (although, the nature of this combining process is not prescribed). The records at the intermediary are referred to as "surrogate records" and the records at the source servers are referred to as "source records". Each surrogate record include one or more identifiers (URIs) for the source record that it identifies, enabling the client to subsequently retrieve the source record directly from the respective source servers.

Method

The method prescribed by this schema is for the surrogate record to identify a source record by a URI, conveyed by TagSet-M element 12. The URI might be a Z39.50R url, or another type of URI that identifies the record. The server might supply multiple URIs (via multiple occurences of TagSet-M element 12) when there exist multiple URIs for the source record.

Purpose of this Schema

The purpose of this schema is to assign specific semantics to the usage of tagSet-M element 12, namely, that it is a URI for the source-record. In the base definition of tagSet-M, element 12 is defined as "url", implicitly, a url for the database record. However, for this model, the base definition leaves open the question of whether the url identifies the actual database record that the result set item points to (i.e. the surrogate record at the intermediary server) or the source record.

When used in the context of this schema, tagSet-M element 12 means URI "for the source record" and not "for the surrogate database record on the intermediary server".

Usage

A server constructing a retrieval record including tagSet-M element 12 to be used in this manner should include the schema identifier for this schema. That is, it should include the following two elements:
  1. tagSet-M element 1: Identifier for this schema, 1.2.840.10003.13.11
  2. tagSet-M element 12: URI for source record. Multiple occurence of this element are allowed, when there are multiple URIs for the source record.
The retrieval record may consist entirely of these two elements. Alternatively (and beyond the scope of this definition), it may also include additional elements, for example metadata about (or from) the source record. In that case, Refer to the clarification Use of nested Schemas for Cross-domain searching and Semantic interoperability for constructing retrieval records with multiple schemas. For example, the two tagSet-M elements above could be the first two elements respectively within the retrieval record, followed perhaps by additional tagSet-M elements, followed by a structured element within which a different schema identifier occurs.

Limitation

This schema assumes for a given record that it is possible to create a URI that uniquely identifies the record. The schema does not address records where no such URI can be created.

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