Which of the five 'walls' bites first in most real projects?

Cardinality — you'll discover within days that you need 'exactly one X'

You hit wall #1 (cardinality) in week 2 of an RDFS-only project. The pragmatic move BEFORE upgrading to OWL is:

Add a SHACL shape with sh:maxCount/sh:minCount — you get the validation you actually wanted, without paying for DL reasoning.

Academy

Where RDFS Hits the Wall

Five things RDFS cannot say — and why you'll need OWL.

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The five walls

Five things RDFS can't say

Cardinality — 'a Person has exactly one date of birth'.
Disjointness — 'no Person is also an Organisation'.
Equivalence — 'foaf:Person is the same class as ex:Human'.
Property characteristics — 'hasAncestor is transitive'.
Defined classes — 'an Adult IS a Person whose age ≥ 18' (sufficient + necessary).

Every one of those is daily work — and every one of them is the reason OWL exists. L2 takes you there.

Driver's licence vs pilot's licence

RDFS is a driver's licence: enough authority to drive a car, sign a delivery slip, prove your age. OWL is a commercial pilot's licence: same skill family (operating a vehicle) but a totally different regulatory regime so you can do things the car licence simply cannot — fly across borders, carry passengers under instrument rules, certify cargo. Trying to fly with a driver's licence is the same category of mistake as trying to express cardinality in RDFS.

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