Meaning of the term " Schema "

Folks
I just want to know the general meaning of the term " Schema " in the database development perspective and from an Oracle perspective.
It will be very helpful if you explain to me in a simple way because I am very new to the Database field
Just started learning sql , pl/sql in ORACLE XE.

Matt wrote:
I just want to know the general meaning of the term " Schema " in the database development perspective and from an Oracle perspective. A schema can be many things.
Typically a schema is what you would call a database in SQL-Server and mySQL. In other words, it is a container for a logical database. Where this logical database consists tables, indexes, stored procs, views, triggers, etc. etc.
A schema also can be used as a user account. For example, schema DB1 is used as a logical database schema. Schema JOHN is created for John Doe to logon to Oracle and use the DB1 logical database. DB1 in this case will need to grant JONH access to its objects (and this way different user schemas can have different rights and access to a logical database schema).
Or a schema can be container for common code. A lot of PL/SQL based applications will have a set of common packages and functions and procedures. This can be stored in a schema that acts as a common code library. The code will typically be defined using caller rights (meaning that if the code is called by schema FOO, the code executes with FOO's rights). Public execute rights are granted.
A schema can be an application schema for a 3 tier system. The application tier (Java system running in JBoss for example) does the user authentication. This app tier needs to talk to the database (i.e. logon using a schema). In this case a special schema is created for the app tier (a so-called "trusted" schema as the database trusts the app tier to authenticate the users in order to gain access to the database). This app schema will then (similar to the JOHN user schema) have rights on the logical database schema.
A schema can be a full blown application framework. Oracle's Apex is an example. Its schema contains the Apex runtime engine and Apex RAD GUI. You develop your application inside this framework (which is stored as data in this app framework schema). This Apex app you develop will usually in turn use a logical database schema.
A schema can also be a combination of some of the above.
The SYS schema for example is the core of the database and contains (amongst others) the data dictionary of the database.
There is a special schema that contains the XMDB (XML database) feature of Oracle.
So Oracle itself uses the concept of containers to bundle specific feature sets together in a logical and secure way.
Schemas can also be physically separated from one another. The DB1 logical database schema can for example use its very own physical storage (Oracle tablespaces).
The great thing about a schema is that it can fill a number of roles - as it provides a secure container and in turn security layers can be created between containers to allow one container (e.g. user schema JOHN) to access/use objects of another container (e.g. logical database schema DB1).
And correctly using schemas are important for flexibility, maintainability and above all, security.

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function(){return A.apply(null,[this].concat($A(arguments)))}
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That's one of those things that one is not supposed to question. It just sounds so right!
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