Hi Sanjit,
It depends on what master data tables are you interested in and what APO functions are you using. Basically most tables are including MATID (Product Guid) or LOCID (Location Guid) which are the core master data. Most higher level functions orient themselves based on Product and Location. Eg. Hierarchies, Transportation Lanes, Interchangeability.
For More info about APO master data you can check:
SCM Master Data - Supply Chain Management (SCM) - SCN Wiki
There are tables mentioned and briefly described as well.
I hope it helps!
Gergely