How to add a property in ServiceNow which calls REST API of another application for look up?

I have an application (JAVA application running on tomcat) which has SACM and ITSM modules similar to servicenow. From my application I am calling servicenow APIs to look up data and create new records in servicenow. Does servicenow allow it vice versa?

Something like add a new property Associated CIs in Incident module, which...