The Semantic Spectrum — Pick Your Rung

Six rungs on one ladder

Rung	Adds	Reasoning power	Cost
Controlled vocab	enumerated terms	none	trivial
Taxonomy	hierarchy	parent/child traversal	low
Thesaurus (SKOS)	broader / narrower / related	navigation, alignment	low
RDFS	classes, properties, domain/range	subsumption	moderate
OWL DL	class expressions, restrictions	classification, consistency	high
OWL + rules	Horn-like rules	derivation beyond DL	very high — decidability at risk

Engineering rule: climb only until your competency questions are answered. Every extra rung adds reasoner complexity, author training cost, and a longer list of consultants in the room.

Think of cooking tools:

• Controlled vocabulary = a labelled jar.
• Taxonomy = a spice rack with categories.
• Thesaurus = the spice rack + cross-references ('paprika ≈ sweet pepper').
• RDFS = a small recipe book — categories with ingredient rules.
• OWL = a full cookbook with chemistry — a recipe that defines what is a soup vs a stew.
• OWL + rules = a Michelin kitchen brigade — exquisite, slow, and overkill for breakfast.

Most teams need a recipe book. Some teams build cookbooks. Almost nobody needs the brigade.