Knowledge in Probase is harnessed from digitized footprints of human behavior and communications.

But Probase is much more than a traditional ontology/taxonomy, which can be seen in three dimensions: the concept dimension, the data dimension, and the relationship dimension.

Compared with other knowledgebases, Probase is unique in two aspects. First, Probase has an extremely large concept/category space (2.7 million categories). As these concepts are automatically acquired from Web pages authored by millions of users, it is probably true that they cover most concepts in our mental world (about worldly facts). Second, data in Probase, as knowledge in our mind, is not black or white. Probase quantifies the uncertainty. These serve as the priors and likelihoods that become the foundations of probabilistic reasoning in Probase. With this probabilistic Probase, we build several interesting applications, such as topic search, Web table search and document understanding.

You can find all the information about the project at http://research.microsoft.com/en-us/projects/probase/