1. A system comprising: a deep network implemented in one or more computers that defines a plurality of layers of non-linear operations, wherein the deep network comprises: an embedding function layer configured to: receive an input comprising a plurality of features of a resource, wherein each feature is a value of a respective attribute of the resource, and process each of the features using a respective embedding function to generate one or more numeric values, and one or more neural network layers configured to: receive the numeric values, and process the numeric values to generate an alternative representation of the features of the resource, wherein processing the numeric values comprises applying one or more non-linear transformations to the numeric values; and a classifier configured to: process the alternative representation of the input to generate a respective relevance score for each concept term in a pre-determined set of concept terms, wherein each of the respective relevance scores measures a predicted relevance of the corresponding concept term to the resource.