Crosswalk Pattern
Context
Multiple classification systems exist for the same domain. Different communities have built their own taxonomies optimized for their needs: military uses occupational codes, education uses instructional program codes, labor statistics use SOC codes. Each serves its users well. None will be abandoned.
Problem
How do you enable interoperability between systems without forcing everyone to adopt a single universal taxonomy?
Solution
Build and maintain explicit mappings (crosswalks) between systems. Accept that:
- Mappings won’t be 1:1 (one occupation may map to several)
- Granularity differs (one system’s detailed category is another’s broad bucket)
- Maintenance is ongoing (changes in either system require crosswalk updates)
O*NET maintains crosswalks to seven different classification systems:
- Military Occupational Classifications (by branch)
- Classification of Instructional Programs (CIP)
- Occupational Outlook Handbook
- Standard Occupational Classification (SOC)
- Dictionary of Occupational Titles (DOT)
- RAPIDS (apprenticeship programs)
- ESCO (European classifications)
Each crosswalk is published, versioned, and updated when either system changes.
Consequences
Benefits:
- Communities keep their optimized taxonomies
- Users can traverse between systems
- No “big bang” migration required
- Incremental adoption possible
Costs:
- Maintenance burden scales with number of systems
- Mapping quality requires domain expertise
- Edge cases need ongoing resolution
- Versioning complexity increases
When to Apply
Use crosswalks when:
- Multiple established taxonomies exist
- Political/practical barriers prevent consolidation
- Different communities have legitimately different needs
- Interoperability matters more than uniformity
Avoid when:
- Starting from scratch (design one good taxonomy instead)
- Only two systems exist (consider actual consolidation)
- Maintenance commitment isn’t sustainable