Database schema is like a name space. Like I have few tables designed for HR purpose and so I name the schema as HR for all these tables like HR.Department, HR.Users and so on.The main use of specifying schema is it would be easy for DBAs to define the permissions. For example,HR department can have read/write/view permissions on all the tables with schema as HR and PR department can have only read permissions on the tables with schema as HR. So, the schemas helps in identifying and setting the permissions on the objects with ease.