Architecture and technologies of the ASDD

The ASDD provides direct access to a number of directory systems distributed throughout Australia as shown in the systems architecture diagram. Each data directory in the ASDD is known as a "node".

The Z39.50 protocol (ISO 23950 information search and retrieve protocol) is used to simultaneously search each of the data directories that form the ASDD. The user composes their search query using the WWW gateway interface. Behind the scenes this is translated into Z39.50-speak by the gateway and then broadcast to each of the specified nodes. The individual nodes process the query separately and return their set of results. The results from each node are shown on the results page in order of response from each of the nodes. Further detail can be found in the ASDD search and retrieve overview.

The WWW-Z39.50 gateway interfaces to the ASDD are based on a ZAP Apache module. More information about Zap can be found at URL: http://www.indexdata.dk/zap/. Anyone can also build their own independent gateway to the ASDD. The underlying Z39.50 servers can also be accessed by true Z39.50 client software (see lists at Z39.50 Maintenance Agency.

The Z39.50 server at each node converts the Z39.50 Use Attributes (the standard numbers behind the WWW interface pick-list names) into field names that are relevant to their particular document collection.

The ASDD is searching directories which are based on XML metadata document collections at all nodes, except at some nodes where a relational database is being accessed to retrieve metadata records.