About the concepts of Database, instance, role, schemas, user, and object in Oracle

When using Oracle, you often hear these words. For what these words are, I saw an easy-to-understand statement from the Internet. I made a slight modification:
1. DATABASE, for Oracle, refers to the physical database. Generally, after you install an Oracle database software, it is a database.

2, instance, on the same database, you can create multiple instances, these instances do not interfere with each other, each instance can have independent table space, user, table, process and other database objects. That is to say, each instance is actually a logical database that we all understand.

3. Schemas, it is easy for you to understand by "user", and each schema (user) can have a set of objects that do not interfere with each other. If you want to access objects in other schemas, you need to specify the name of the schema, which is actually the username.
For example, if you want to access the table emp of the schema scott, and your schema (user) is tiger, then you should write:
select * from scott.emp;
role is the login identity used by the user, such as as dba

4. Object, the object is actually the table, view, procedure and so on that we commonly use.

These relationships can be said to be:
There are multiple logical databases (instance) under the physical database (Database)
There are multiple users (user) under the logical database (instance)
The user (user) corresponds to a default scheme (schema) and can log in to the database using the owned role (role)
There are multiple user objects (object) under the user

In addition, you can refer to http://blog.csdn.net/blognkliming/article/details/7613189 for some detailed explanations