In general, one aspect of the subject matter described can be embodied in a method that includes receiving a first repair request for a first computer hardware component and receiving a second repair request for a second computer hardware component. The method can further include selecting first numerical tokens to describe the first repair request and selecting second numerical tokens to describe the second repair request, wherein each of the first and second tokens are associated with a different level of a hierarchy of tokens. The method can additionally include, for each level of the hierarchy of tokens, selecting each unique individual token associated with the level of the hierarchy of tokens from the first tokens and from the second tokens. The method can further include determining an aggregate cost of the first request and the second request from the selected unique individual tokens.