Two-Pillar Taxonomy Architecture

The Framework

Separate taxonomies for “what people do” (occupations) and “what people can do” (skills/competences), connected through typed relationships.

Why This Matters

The naive approach, embedding skills directly under occupations, creates several problems:

1. The same skill appears redundantly under every occupation that needs it
2. Skill portability becomes invisible (can’t see that “project management” transfers across roles)
3. New occupations require rebuilding the entire skill inventory from scratch

The two-pillar approach solves this by treating occupations and skills as first-class entities in their own hierarchies, then connecting them with explicit relationships.

How It Works

Occupations pillar:

• Hierarchical structure (ESCO extends ISCO-08)
• Broad groups narrow to specific occupations
• Each occupation has an occupational profile listing associated skills

Skills pillar:

• Independent hierarchy organized by reusability level
• Skills can connect to multiple occupations
• Reusability levels indicate portability (transversal → occupation-specific)

Relationships:

• Essential: skill required for this occupation regardless of context
• Optional: skill may be required depending on employer/specialization/region

When to Use

When building any professional/competency taxonomy. When skills need to be tracked independently of roles. When demonstrating skill transferability matters (career transitions, reskilling programs).

Limitations

• More complex to maintain than a flat occupation→skills model
• Requires careful governance to keep pillars aligned
• Essential/optional distinction is contextual, what’s essential in one region may be optional in another

Related: 06-molecule—ontology-design-patterns