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MARC XML Design ConsiderationsThe Library of Congress' Network Development and MARC Standards Office is developing a framework for working with MARC data in a XML environment. This framework is intended to be flexible and extensible to allow users to work with MARC data in ways specific to their needs. The framework will contain many components such as schemas, stylesheets, and software tools developed and maintained by the Library of Congress.
1. Simple and Flexible MARC XML Schema
The core of the MARC XML framework is a simple XML schema which contains MARC data. This base schema output can be used where full MARC records are needed or act as a "bus" to enable MARC data records to go through further transformations such as toDublin Core and/or processes such as validation. The MARC XML schema will not need to be edited to reflect minor changes to MARC21. The schema retains the semantics of MARC.
All control fields, including the leader are treated as a data string. Fields are treated as elements with the tag as an attribute and indicators treated as attributes. Subfields are treated as subelements with the subfield code as an attribute.
2. Lossless Conversion of MARC to XML
All of the essential data in a MARC record is converted and expressed in XML. MARC structrual elements, such as the length of field and starting position of field data in directory entries are not needed in the XML record. Leader data positions not needed in the XML environment are retained as place holders or carried as blanks.
3. Roundtripability from XML back to MARC
As a consequence of the lossless conversion from MARC (2709), information in a MARC XML record enables recreation of a MARC (2709) record without loss of data. A MARC (2709) record can also be created without data loss from MARC XML records.
4. Data Presentation
Once MARC data has been converted to XML, data presentation is possible by writing a XML stylesheet to select the MARC elements to be displayed and to apply the appropriate markup.
5. MARC Editing
Some single or batch updates such as adding, updating, or deleting a field to a MARC record can be accomplished with simple XML transformations
6. Data Conversion
Most data conversions can be written as XML transformations. For more complex transformations of the data, software tools which read MARC XML can be written.
7. Validation of MARC data
Validation with this schema is accomplished via a software tool. This software, external to the schema, will provide three possible levels of validation:
By using XML as the structure for MARC records, users of the MARC in the XML framework can more easily write their own tools to consume, manipulate, and convert MARC data.