10. The system of claim 8 , wherein the numeric representations are vectors of floating point values.
8. A system comprising one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations comprising: receiving an input comprising a plurality of features of a resource, wherein each of the features is of a different feature type; generating an alternative representation of the features of the resource, comprising: generating a respective numeric representation of each the features by processing each of the features using a respective embedding function, wherein each of the embedding functions is specific to features of a respective feature type, and processing the respective numeric representations through one or more neural network layers to generate the alternative representation; and providing the alternative representation of the features of the resource as input to a neural network classifier for classification of a relevance of a plurality of concept terms to the resource.