Schema Crosswalk - Challenges For Crosswalks

Challenges For Crosswalks

One of the biggest challenges for crosswalks is that no two metadata schemes are 100% equivalent. One scheme may have a field that doesn't exist in another scheme, or it may have a field that is split into two different fields in another scheme; this is why you often lose data when mapping from a complex scheme to a simpler one. For example, when mapping from MARC to Simple Dublin Core, you lose the distinction between types of titles:

Simple Dublin Core only has one single "Title" element so all of the different types of MARC titles get lumped together without any further distinctions. This is called "many-to-one" mapping. This is also why, once you've translated these titles into Simple Dublin Core you can't translate them back into MARC. Once they're Simple Dublin Core you've lost the MARC information about what types of titles they are so when you map from Simple Dublin Core back to MARC, all the data in the "Title" element maps to the basic MARC 245 Title Statement field.

This is why crosswalks are said to be "lateral" (one-way) mappings from one scheme to another. Separate crosswalks would be required to map from scheme A to scheme B and from scheme B to scheme A.