Something about oracle inventory

The inventory is created once you install Database or used for upgrades and patches. two kind of oracle inventory  one called central inventory per server and another one called local inventory for each ORACLE_HOME, the difference between each of them central inventory basically contains a high-level list of components installed on the server. It is updated each time components are installed or uninstalled but it does not have detailed information such as the patch level of each ORACLE_HOME. on another hand  local inventory  contains some component information included with patch-level information.

another different is The Central Inventory contains the information related to all Oracle products installed on a host. and consists of a file called inventory.xml, which lists all the Oracle Homes installed on the node.
for local inventory ( $ORACLE_HOME/inventory ) that contains the detail of the patch level for that ORACLE_HOME. The Local Inventory gets updated whenever a patch is applied to the ORACLE_HOME, using OUI. If the Local Inventory becomes corrupt or is lost, this is very difficult to recover, and may result in having to reinstall the ORACLE_HOME and re-apply all patchsets and patches.

For More Information about this topic refer to MOS :
 Global and Local Inventory explained [ID 360079.1]
FAQs on Central Inventory and Oracle Home Inventory (Local Inventory) in Oracle RDBMS [ID 564192.1]