Integrating SAP and non SAP applications

I am trying to integrate a java application with sap using XI. In java application i will enter the materials name and all the reqired details about the material will be fetched from MM module through XI back to Java application.

Java Application -

> HTTP Adapter -

> XI -

> RFC Adapter (Synch interface) -

> R/3

If i have to input the material name in my java application for which all the info would be extracted from the MM module, than where do i define the data type of the parameter that would be sent and the data types of the information that would be retrieved from the MM module. How would XI differentiate between the two.