2. create a RELATIONSHIP to DOCLINK OBJECT
Application Name: Custom_App3. Enlist you custom application in APPDOCTYPE table, for that run this insert statement
Relationship: DOCLINKS
child Object: DOCLINKS
Where Clause: ownertable='Custom_App' and ownerid=:Custom_AppID
INSERT INTO MAXIMO.APPDOCTYPE (APP, DOCTYPE, APPDOCTYPEID) VALUES ('Custom_App', 'Attachments', (NEXT VALUE FOR MAXIMO.APPDOCTYPESEQ));