1. A computer-implemented method for determining user interests, comprising: receiving user activity data that describes an interaction between a user and digital content; generating first interest-level data that quantifies a first level of interest between said user and an entity that is a topic of said digital content, wherein said entity is one of a plurality of entities included within a knowledge base, said knowledge base comprising an ontology that indicates relationships between said plurality of entities; identifying a candidate entity based on said candidate entity having one of said relationships to said entity within said knowledge base; and generating second interest-level data that quantifies a second level of interest between said user and said candidate entity based on an analysis of said one of said relationships of said candidate entity to said entity within said knowledge base.