Understanding of Oracle multi-tenant PDBs I'm a new user to Oracle. The document states


  The CDB root, also called simply the root, is a collection of schemas, schema objects, and nonschema objects to which all PDBs belong.


and


  A PDB is a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a non-CDB. 


So both CDB and PDB are a collection of schema, schema objects and nonschema objects. How could PDBs belong to CDBs? What does it mean by something like schema object a belong to schema object b?
It simply means a PDB looks like a normal database instance. When you log into a PDB you only see the users and their database objects which belong to that PDB. The CDB is the actual sever instance, and it has the objects it needs for maintaining the server. In the CDB you can log in, and the tables there have a new column to mark the records associated with a specific PDB.