1. Darwin: it uses the principles of specialization and inheritance
2. Information Typing: it capitalizes on the semantics of topics (concept, task, reference) and of content (messages, typed phrases, semantic tables)
3. Architecture: it provides vertical headroom (new applications) and edgewise extension (specialization into new types) for information

This architecture supports the proper construction of specialized DTDs from any higher-level DTD or schema. The base DTD is ditabase DTD, which contains an archetype topic structure and three additional peer topics that are typed specializations from the basic topic: concept, task, and reftopic. The principles of specialization and inheritance resemble the principle of variation in species proposed by Charles Darwin. So the name reminds us of the key extensibility mechanism inherent in the architecture.