ASDD Z39.50 search and retrieve overview

Note: This document explains ASDD Z39.50 search and retrieve using Isite as an example. However, these notes apply to all Z39.50 servers that wish to participate in the ASDD. See ASDD Architecture Diagram

Z39.50 servers can connect to any back-end document management system. Documents can be stored in any brand of database, or as a collection of SGML/XML text files. Each particular server can interrogate many back-end document collections. Importantly, this enables the custodian to leave their existing document management systems in place and simply install a front-end interface to index and serve them.

The ASDD user-interface is an HTML form and associated broker software (HTTP-Z39.50 gateway) which could reside at any node (currently only at Geoscience Australia). The broker initiates the broadcast query to all of the selected Z39.50 servers, then monitors progress and delivers results back to the user as a dynamic web page. The user can select a particular document from the result set. The broker retrieves an HTML copy of the relevant metadata document by way of the distributed custodian node's Z39.50 server and presents it through the Web server of the initiating node.

A Z39.50 server that uses Isite has two ways of interacting with the data. One way is for Isite to pass the search or presentation request off to a relational database. The other way is for Isite to use its inbuilt "Isearch" application. Isearch uses programs called "doctypes" which know how to read and interpret metadata as structured text files. Specifically there are two Isearch doctypes for parsing geospatial metadata in SGML (Standard Generalized Markup Language) or eXtensible Markup Language (XML) format. The SGML/XML metadata documents must conform to the ANZMETA SGML/XML Document Type Definition (DTD) for geospatial metadata which defines the document structure and required elements. The Isearch doctype "anzmeta" is for the current version of the ANZMETA DTD. The Isearch doctype "anzlic" is for old, basic metadata.

Z39.50 uses "Element Sets" to specify how the search results will be returned to the client. If the client specifies a "brief" element set ("B") then the server will return a list of hits (the title of each document that matches the query). If the client specifies a "full" element set ("F") then the server will present the relevant full document. Other element sets can be used to retrieve specific elements from the metadata documents (e.g. Element Set "A" could give title + abstract).

The Isearch doctypes will present a particular full document simply by substituting the filename extension. If the client requested a "Record Syntax" (presentation format) of HTML then the doctype will add the ".html" or ".htm" extension and present that pre-prepared document. If the client requested a "Record Syntax" of SUTRS (Simple Unstructured Text Record Syntax) then the doctype will add the ".txt" extension and present the plain text version of the document. XML (eXtensible Markup Language) has a registered Z39.50 Record Syntax Object Identifier (OID). Some WWW browsers do not yet support XML. However, it can be delivered if the client so requests.