Ontopia has a web service interface which provides a number of generic requests such as get-topic, get-tolog (query results), delete-topic, add-fragment (in some Topic Maps syntax), and so on. This interface is exposed both as a plain HTTP interface and using SOAP, so that requests can be sent using both styles. 

The web service interface is used by the graphical visualization applet to lazily download a topic map fragment by fragment as the user browses the topic map in the applet.