1. A method comprising: accessing, by one or more computers, a hierarchical network of connected concepts that defines a semantic space, the concepts being connected to one another through connections that have different strength values and different types of relationships, the relationships including (i) a parent-child type of relationship that connects concepts in a first direction in the hierarchical network, (ii) a child-parent type of relationship that connects concepts in a second, different direction in the hierarchical network, and (iii) a lateral bond type of relationship that connects concepts in a third, different direction in the hierarchical network; identifying multiple connections that define a path between a first concept and a second concept in the hierarchical network; aggregating the strength values of the multiple connections that define the path; determining that one or more changes in direction occur along the path; scaling, by one or more computers, the aggregated strength value using a penalty factor based on determining that one or more changes in direction that occur along the path; and assigning the scaled strength value as a value that quantifies a proximity of the first concept to the second concept in the semantic space.