Discovering land transaction relations from land deeds of Taiwan

Land deeds were the only proof of ownership in pre-1900 Taiwan. They are indispensable for the studies of Taiwan's social, anthropological, and economic evolution. We have built a full-text digital library that contains almost 40,000 land deeds. The deeds in our collection range over 250 years and are collected from over 100 sources. The unprecedented volume and diversity of the sources provide an exciting source of primary documents for historians. But they also pose an interesting challenge: how to tell if two land deeds are related. In this article, we describe an approach to discover two important relations: successive transactions and allotment agreements involving the same property. Our method enabled us to construct 6,035 such transaction pairs. We also introduce a notion of 'land transitivity graph' to capture the transitivity embedded in these transactions. We discovered 2,436 such graphs, the largest of which includes 104 deeds. Some of these graphs involve land behavior that had never been studied before.