1. A method for operating a publish-subscribe data messaging system, the method comprising: receiving at a first computer-hosted software application a publication topic associated with a data publication, wherein the publication topic is expressed as a hierarchy of topic levels; selecting a formatting rule associated with a wildcard subscription that is represented in a collection of subscriptions of a second computer-hosted software application, wherein the wildcard subscription is expressed as a hierarchy of topic levels, and wherein the formatting rule identifies at least one topic level of the wildcard subscription that is represented with a wildcard token; for each topic level of the wildcard subscription that the formatting rule indicates is represented with a wildcard token, and that corresponds to a topic level of the publication topic, replacing the corresponding topic level of the publication topic with the wildcard token from the corresponding topic level of the wildcard subscription, thereby creating a wildcard version of the publication topic; determining if a match exists in the collection of subscriptions for the wildcard version of the publication topic; and if the match exists, forwarding the data publication from the first computer-hosted software application to the second computer-hosted software application via a data communications medium.