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Technical Notes

The PADI website was developed in two phases. In phase 1 (released in 1999) PADI was migrated from manually-edited lists of resources to a subject gateway service with a browse interface refreshed dynamically from a metadata repository and a search interface enabling users to search the repository using a range of search criteria, including fielded searching. In phase 2 (released in 2001) a distributed update capability was developed that has enabled maintenance of the repository to be shared with other agencies.

The metadata repository is based on Oracle, the search interface uses Inktomi Enterprise Search (Ultraseek) and the application has been developed using the WebMacro Java servlet framework.

Specifications for the PADI Subject Gateway Project were developed taking into account the National Library of Australia's Best Practice Checklist for Australian Subject Gateways. An assessment of the extent to which PADI meets best practice according to this checklist is given below:

Content Characteristics | Business Characteristics | Functional Characteristics

Content Characteristics

The gateway may describe both print and electronic resources. It should be noted that gateways currently carry with them an expectation of access to content in real time.

PADI describes quality digital preservation resources regardless of format. Where there is no direct access to content, users have the option of viewing the full repository record, where there may be more information about the availability of the resource.

The gateway may include professionally produced descriptions of the resources. Such descriptions may pertain to the content of the resource, in a form ranging from a short annotation to a review. Metadata will be applied to facilitate the description of other attributes of the resource, such as its title, author, format or location.

PADI resource descriptions are created by information professionals from each of the participating agencies using metadata appropriate to the description of each resource type.

The resource types included may describe people, places, events, works

PADI describes events and works. The same metadata schema is used for both to simplify maintenance and processing issues. A separate schema for describing events may be considered as an enhancement when standards in this area have evolved.

Works may be described at collection, whole item, part item or analytical level.

PADI describes works at any of these levels if they fall within scope. Four types of relationship are supported by the PADI Metadata Schema: Is Review Of, Is Paper Of, Is Part Of and Is Archived Version Of.

Resources should be indexed according to a recognised subject classification scheme in order to enable subject browsing. Controlled vocabulary systems such as subject heading lists and thesauri should be used in this process.

PADI resources are described using the PADI Thesaurus.

The resources described in the gateway may be uniquely Australian, or of high use value within Australia.

PADI is being developed with appropriate partners as an international subject gateway. PADI content will be of high use value within Australia and overseas.

The resources linked from the gateway must go through a selection process conducted by the jurisdiction responsible for the gateway, to ensure a high level of quality and relevance to the subject matter. There should be a written policy listing selection criteria to facilitate this process.

The National Library of Australia manages this process with the help of an international advisory committee. A document outlining the PADI Selection Criteria is publicly accessible from the PADI web site.

The resources must have their currency maintained. This may be managed by sub-jurisdictional partners through human intervention, or by an automated process, or by a combination of both strategies. There should be a written policy detailing collection maintenance issues and procedures.

The National Library of Australia is committed to providing the resources needed to maintain the currency of the PADI service. The PADI Subject Gateway Project minimises the costs of meeting this criterion by automating processses and enabling the workload to be shared with partners via distributed data entry and review.Collection maintenance issues and procedures are documented in PADIUpdate Help which is accessible to all registered users of the distributed PADI update function.

The metadata describing the resources in the gateway must meet a recognised standard for resource discovery ...

PADI uses the Dublin Core metadata schema in all processes involving interoperability with other systems.

Extensions to the above-listed metadata may be created, but must be managed through cooperative, responsible and secure processes, to ensure Australian best practice in standards application.

The full PADI metadata schema is described on this site.

The copyright of resources linked from the gateway may be managed by the sub-jurisdictional partners or by the host partner.

Copyright of resources is recorded where publically available. PADI does not extend to the management of copyright, which is seen as the responsibility of the publisher.

Business Characteristics

The gateway should be hosted in Australia, although it may be mirrored internationally.

PADI is hosted by the National Library of Australia.

The gateway host should have recognised jurisdictional carriage of the subject area, either through a statutory or other clear obligation.

The National Library of Australia is recognised nationally and internationally as a centre of excellence in the area of digital preservation.

Contributions to the gateway must be made by a range of partnered organisations and institutions, not a single business entity.

The technical infrastructure supports the development of formal business arrangements with partners who wish to contribute to the gateway.

The gateway should be promoted through more than one Australian entry point.

PADI is promoted through a range of entry points, both in Australia and overseas.

The gateway may provide links to other Australian, and overseas, gateways.

PADI lists such gateways as resources.

The gateway must ensure the long-term sustainability of its service, which may be addressed by a strategic plan covering business and marketing issues.

This is being addressed both in business and system terms.

The gateway should address the responsibility of long-term access to content by taking on a management and preservation role for the Australian resources within its purview, or by supporting national initiatives which aim to do so...

This is being addressed through the Safekeeping Project.

Functional Characteristics

The gateway must support both browse and search access through the use of a metadata-enabled search engine and other value-added features.

PADI has both browse and search interfaces generated dynamically from a metadata repository. Important value-added features are the ability to search the PADI Thesaurus and the ability to conduct a full-text search of linked web sites. In the current version, only the linked page is indexed. An element has been added to the PADI resource record to enable PADI managers to record the level to which the site should be indexed for this service.

The selection criteria used to identify resources, and the metadata schema used to describe them, should be made publicly accessible.

PADI is a subject gateway to digital preservation resources. A document outlining the PADI Selection Criteria is publicly accessible from the PADI web site. The PADI Metadata Schema is published on the PADI Web Site.

The Web access component of the gateway must support a link to the actual content of a resource or its digital surrogate.

Where online content exists, PADI includes a link. The PADI service would not be sustainable if content had to be created as part of the indexing process for resources not directly accessible online. It is considered more important that quality digital preservation resources are brought to users' attention regardless of format, than that user's expectations for direct access are met in all cases. For material not directly accessible online a full resource description acts as the digital surrogate.

The gateway may provide links to related free or paid services, but without a mandatory requirement to provide e-commerce support for them. It should be noted that gateways currently carry with them an expectation of free access.

PADI is freely accessible and provides no e-commerce support.

Access to each type of resource may be exploited by alternative entry points within the same gateway.

A variety of sorting and filtering mechanisms are applied to the resources indexed for PADI depending on resource type.

The gateway should meet accessibility criteria as outlined by the W3C Web Accessibility Initiative, in their Web Content Accessibility Guidelines. The content should be accessible to everyone, including users with disabilities and users of text-only browsers.

The PADI web site meets Conformance Level A of the W3C Web Content Accessibility Guidelines.

The gateway should make provision to support a standard form of cross-gateway-searching, such as Z39.50 or HTTP.

Dublin Core metadata is embedded in all pages generated as part of the Browse interface. Gateways harvesting this metadata will be indexing PADI outputs consisting of lists of resources on a given topic or in a given category. Individual PADI resource records are also available in the form of metafiles containing embedded DC metadata in the head section and the displayed record in the body. These metafiles are the mechanism currently used to generate the indexes to support the search function. They are not publicly accessible but could be provided to another gateway under a formal business arrangement. The Inktomi Enterprise Search (Ultraseek) also supports the Z39.50 search and retrieval protocol.

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