An ontology is a computer-processable collection of knowledge about the world.
This thesis explains how an ontology can be constructed and expanded auto-
matically. The proposed approach consists of three contributions:
1. A core ontology, YAGO.
YAGO is an ontology that has been constructed automatically. It com-
bines high accuracy with large coverage and serves as a core that can be
2. A tool for information extraction, LEILA.
LEILA is a system that can extract knowledge from natural language
texts. LEILA will be used to ¯nd new facts for YAGO.
3. An integration mechanism, SOFIE.
SOFIE is a system that can reason on the plausibility of new knowl-
edge. SOFIE will assess the facts found by LEILA and integrate them
Each of these components comes with a fully implemented system. Together,
they form an integrative architecture, which does not only gather new facts,
but also reconcile them with the existing facts. The result is an ever-growing,
yet highly accurate ontological knowledge base. A survey of applications of the
ontology completes the thesis.