1. A method comprising: carrying out offline functionality-based co-ranking and clustering on a knowledge base, said knowledge base characterizing a heterogeneous information technology services network comprising a plurality of services, a plurality of providers, and a plurality of attributes; storing results of said functionality-based co-ranking and clustering as annotations of said services and said providers in said knowledge base, to obtain an annotated knowledge base; obtaining a service requirement from a customer requiring information technology services; querying said annotated knowledge base, based on said service requirement; and returning to said customer an ordered list of at least given ones of said services, based on said querying.