The paper discusses issues related to the use of faceted classifications in an online environment. The author argues that knowledge organization systems can be fully utilized in information retrieval only if they are exposed and made available for machine processing. The experience with classification automation to date may be used to speed up and ease the conversion of existing faceted schemes or the creation of management tools for new systems. The author suggests that it is possible to agree on a set of functional requirements for supporting faceted classifications online that are equally relevant for the maintenance of classifications, the creation of classification indexing tools, or the management of classifications in an authority file. It is suggested that a set of requirements for analytico-synthetic classifications may be put forward to improve standards for the use and exchange of knowledge organization systems.