[this last section is out of date and is pending an update]
eSTEM works through a standard web service communicating over HTTP/HTTPS via SOAP as defined by the relevant standards (see http://www.w3.org/2002/ws/ and http://msdn.microsoft.com/en-us/library/ms951274.aspx). The URL by which the service is accessed is controlled by the administrator of the eSTEM server. Implied Logic’s own service is at http://stem.impliedlogic.com/STEMWebService.asmx and you can obtain a WSDL description of the inputs and outputs of the service from there.
The web service provides a single method named RunModel. This is the only access point that web-based users have to the service. This method takes as inputs the model identifier string created when the model was exported from STEM and an array of inputs. The exact set of inputs exported by the modeller from STEM must be provided, in exactly the order specified in WebServiceModelConfig.txt. If this is not the case, the web service will respond with an error message and will not run the model.
If the inputs to the RunModel method are suitable, then the web service will set those inputs on a copy of the model, run it and return the results of that run. The results returned will be exactly the set of results selected by the modeller when exporting from the STEM Results Program, and thus defined in WebServiceModelConfig.txt.