14. A system for creating a hierarchy of topics, the system comprising: a processor; a memory communicatively coupled to the processor and including instructions, when performed by the processor cause the system to perform operations to: training a skill classifier using training data, the training data comprising a plurality of skill pairs, each skill in the plurality of skill pairs selected from a predetermined list of skills; determining for each particular skill pair in a target set of skill pairs, using the skill classifier and feature data, a probability that a first skill in each particular skill pair is a parent of a second skill in each particular skill pair, the first and second skills included in the predetermined list of skills; wherein the feature data includes a ratio of a number of times the first skill was explicitly included in member profiles of a social networking service to a number of times the first skill was implicitly included in member profiles of the social networking service; collecting, in response to the determining the probability for each particular skill pair, a collection of probabilities for the target set of skill pairs; and constructing a hierarchy of skills based upon the collection of probabilities for the target set of skill pairs.
14. A system for creating a hierarchy of topics, the system comprising: a processor; a memory communicatively coupled to the processor and including instructions, when performed by the processor cause the system to perform operations to: training a skill classifier using training data, the training data comprising a plurality of skill pairs, each skill in the plurality of skill pairs selected from a predetermined list of skills; determining for each particular skill pair in a target set of skill pairs, using the skill classifier and feature data, a probability that a first skill in each particular skill pair is a parent of a second skill in each particular skill pair, the first and second skills included in the predetermined list of skills; wherein the feature data includes a ratio of a number of times the first skill was explicitly included in member profiles of a social networking service to a number of times the first skill was implicitly included in member profiles of the social networking service; collecting, in response to the determining the probability for each particular skill pair, a collection of probabilities for the target set of skill pairs; and constructing a hierarchy of skills based upon the collection of probabilities for the target set of skill pairs. 18. The system of claim 14 , wherein the training data comprises feature data and for each particular pair of skills in the training data a designation of whether a first skill in the particular pair of skills is a parent skill of a second skill in the particular pair of skills.