Yes, you need to provide the fact Id inroder to read the fact BO instance in read mode. Additionally, if you need to display the schema for debugging purpose you can make use of % and + operators in script. Refer script tips (View a list of edit data step type commands) for details.
sample code to read the fact BO instance
declareBO "factBOName_Xpath" as 'fact_schema';
move ".../factId" to "fact_schema/factId";
invokeBO "factBO_Xpath" using "fact_schema" for read;