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Mapping and Crosswalking

Mapping and Crosswalking. “Absolute Crosswalking” “Relative Crosswalking” “Switching-across”. Think of mapping between a DC record and a LOM record. A LOM record (partial) hierarchical structure (not flat) many more elements than DC several elements correspond to one DC element.

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Mapping and Crosswalking

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  1. Mapping and Crosswalking “Absolute Crosswalking” “Relative Crosswalking” “Switching-across”

  2. Think of mapping between a DC record and a LOM record • A LOM record (partial) • hierarchical structure (not flat) • many more elements than DC • several elements correspond to one DC element

  3. Absolute Absolute Relative Relative target crosswalking crosswalking crosswalking crosswalking source VAR Core (3.0) VAR Core (3.0) Dublin Core Dublin Core Dublin Core Dublin Core Technique Technique ---------- ---------- Format Format Location.Current Location.Current ---------- ---------- Contributor Contributor Repository Repository Coverage Coverage Common Crosswalking Approaches

  4. Pros and Cons -- Absolute Crosswalking • ensures the equivalency (or closely-equivalent matches) of elements • does not work well for data conversion • data values in non-mappable space will be left out, especially when a source schema has a richer structure than that of the target schema. • E.g., from LOM records to DC records vra:title = dc:titlevra:technique = xxx

  5. Pros and Cons -- Relative Crosswalking • When data conversion is conducted, at least the values in the fields of a source database will find a place to reside in the target database. • Appears to work better when mapping from complex to simpler schema, e.g., from MARC to DC, but not vice versa. http://www.loc.gov/marc/marc2dc.html • The problem is that mapped elements are not really equivalent. vra:title = dc:titlevra:technique = dc:format

  6. Problems exist in direct mapping when: • converting from a less inclusive format to a more inclusive format, • converting from an uncontrolled vocabulary content to a controlled vocabulary content, • converting to fields where there are indirect impacts on the corresponding fields and values, (e.g., 043 and 6xx #z), • data contents using different controlled vocabularies, • data being converted into non-searchable fields.

  7. Incorrect element mapping missed?! missed?! before … OPTIONS mapped to SUBJECT, missing all KEYWORDS after … missing keywords

  8. AUTHOR mapped to DESCRIPTION before … after … noCREATOR 3357 records !

  9. after … Incorrect values before … If re-generate records based on the embedded metadata, all can be corrected.

  10. Inappropriate mapping before … missed? missed? after … CLASSIFICATION mapped to SUBJECT and missed all the KEYWORDs.

  11. Missed Data Values • When a group of elements map to a single one, there could be missed data values. dc:rights

  12. Missed Data Values which may cause in-accessible IDs • WHY do some data sets have 100% inaccessible IDs in a repository after a few years? • The IDENTIFIER only provided the information of the record, such as a local access number ID. • When data were migrated or moved around in these collections’ servers, these IDs became obsolete.

  13. From a LOM record: 3 identifiers • When crosswalking, there should be multiple elements mapped to dc:identifier element

  14. Switching-across when multiple schemas are involved.

  15. Mapping Process • One of the schemas is used as the switching mechanism among multiple schemas. • Instead of mapping between every pair in the group, each of the individual metadata schemas is mapped to the switching schema only. • Example: http://www.getty.edu/research/conducting_research/standards/intrometadata/metadata_element_sets.html

  16. Common properties in crosswalks • definition of each metadata element • mandatory, optional, or mandatory based on certain conditions • may occur multiple times • constraints due to the structure • e.g., hierarchical parent-child relationships • constraints imposed on the value • e.g., free text, numeric range, date, or a controlled vocabulary • locally defined metadata element (s) - Based on St. Pierre and Jr. William. 1998. Issues in Crosswalking Content Metadata Standards. Bethesda, MD: NISO Press.

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