Well, darling, in Oracle, a user is an account used to log in and access the database, while a schema is a collection of database objects (tables, views, etc.) associated with a particular user. So, think of a user as the key to the front door, and a schema as the fancy furniture and decor inside the house. You can have multiple schemas in a single user account, just like you can have multiple rooms in a house. Easy peasy lemon squeezy!
A user in Oracle corresponds to a schema. Objects, such as table and indexes, must exist within a schema. Without creating a user/schema, use of the database will be limited to the built-in schemas and objects, such as the one-row DUAL table and standard PL/SQL packages.
In DB2, a user is an individual who is granted permissions to access and interact with the database, while a schema is a named collection of tables, views, procedures, and other database objects owned by a user. Users are associated with schemas to define their default schema for objects they create.
Database schema are the logical structure of entities (tables or object classes) and their relationships (keys, or object associations) in a database. Schema can exist at different levels of abstraction (see: en.wikipedia.org/wiki/Database_schema). Schema themselves may or may not exist as such in a database. In general schema at the higher levels of abstraction are design models that are captured in printed documents, and authored by business analysts and database designers, rather than created by database programmers and stored in the database itself. But in some types of databases, schema at any level of abstaction can be realized physically. In Oracle databases, schema can be realized as schema objects, which are a part of an Oracle database. These schema objects may represent a human user's conceptual model of the knowledge captured in an enterprise database. Thus defined, there can be many schema that can be associated with one physical database. In other kinds of relational database, an abstract user's schema can be represented by logically linked metadata, views, and stored procedures assocated with a user class. In object-oriented databases, especially those based on the highly self-referential language Smalltalk (e.g. Gemstone/S), schema are realized as "physical" objects in the database as a matter of course, as well as in the logical models captured in design documents. The schema objects in such databases are, in essence, the classes comprising the infrastructure of the database or application. Oracle-style user schema are readily created; these would be realized as user interface orchestrator classes.
SQL*PLUS is a interface between user and Oracle database. It Provide an environment to use the SQL which is a query language to communicate with oracle database
external schema
the difference between end user system and organisational system
An active directory schema allows the user to perform a detailed search for an individual, place or other piece of information. A well designed schema represents software that gives the user access to information within an organization. The structure becomes more detailed as the schema becomes detailed.
The role of the external schema is to support user views of data and thus to provide programmers with easier data access
exlain the differnce between an employing and user organisation
registry
A Database has three views. The External Schema: What the end user sees. The Internal Schema: What the programmers of the program see. The Conceptual Schema: The basic plan of the database. Most of the time this is in paper form as a Conceptual Schema Diagram (CSD)
Use the Oracle revoke command Example: revoke execute on procedure from user;