NGDF Metadata Gateway

Architecture V1.1

3. Metadata Management Systems

3.1 Metadata Collection
The NGDF Gateway is reliant on organisations documenting metadata and making it available from a directory node. To ensure consistent and effective searching from the Gateway, NGDF has defined a structure for metadata content and format. Agencies collect and manage metadata using data management systems compliant with their organisational requirements. Depending on the complexity and constancy of datasets will dictate whether agencies manage metadata in a relational database, spreadsheet or text document. Agencies will also assess whether data is managed locally, centrally or in a distributed environment. Appendix A lists a number of the available metadata management and collection tools.

The manner of data storage is not important for the delivery of the Gateway, however, it is important for the NGDF project that these data management systems:
  1. include, as a minimum, the required elements from the NGDF Discovery to enable searching from the NGDF Gateway and
  2. provide metadata in a format that can be used by the local metadata index. The provider of the local metadata index service will determine the appropriate format to be used, however, NGDF have specified a format based on XML (Extendable Mark-up Language) to assist the transfer of NGDF compliant metadata.

There is also an expectation that specifications for the content and format will be updated to comply with the ISO metadata standard when it is ratified (anticipated late in 2000).

3.2 XML
XML is based on the International Standard Generalised Markup Language (SGML). SGML is a text based format that allows for structured exchange format and for flexible presentation (e.g. HTML is a by-product of SGML). XML has been promoted more recently as the industry standard for storing structured data on the Internet. The NGDF Document Type Definition (DTD) specifies the XML format for the transfer of NGDF metadata to the distributed metadata indexes. There is also an expectation that specifications for the content and format will be updated to comply with the ISO metadata standard when it is ratified (anticipated late in 2000).

3.3 Metadata Validation
Each distributed directory service will require compliant output from organisations wanting to promote their data through the distributed directory service and the Gateway. Individual directory service providers will validate and process supplied metadata to ensure NGDF compliance required for the local and NGDF Gateway. Typically each directory service will request data in either XML or another standard text based output which can be "parsed" to validate the content and process the required XML, HTML or text files.

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