Editing Database schema (section)

==Oracle database specificity==
In the context of [[Oracle Database]]s, a '''schema object''' is a logical data storage structure.<ref>{{cite book
 |first1       = Lance
 |last1        = Ashdown
 |first2       = Tom
 |last2        = Kyte
 |others       = ''et al''.
 |title        = Oracle Database Concepts 11g Release 2 (11.2)
 |url          = http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/tablecls.htm#CNCPT111
 |access-date   = 2010-04-14
 |date         = February 2010
 |publisher    = Oracle Corporation
 |quote        = A database schema is a logical container for data structures, called schema objects. Examples of schema objects are tables and indexes.
 |archive-url  = https://web.archive.org/web/20100129054802/http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/tablecls.htm#CNCPT111
 |archive-date = January 29, 2010
 |url-status     = dead
}}</ref>

An Oracle database associates a separate schema with each database '''user'''.<ref>
{{cite book
|title= Oracle Database Concepts 10g Release 2 (10.2)Part Number B14220-02 
|url= http://docs.oracle.com/cd/B19306_01/server.102/b14220/schema.htm
|access-date= 2012-11-26
|quote= A schema is a collection of logical structures of data, or schema objects. A schema is owned by a database user and has the same name as that user. Each user owns a single schema. Schema objects can be created and manipulated with SQL. 
}}</ref>
A schema comprises a collection of schema objects. Examples of schema objects include:

* [[Table (database)|tables]]
* [[View (database)|views]]
* [[sequence]]s
* [[Synonym (database)|synonyms]]
* [[Index (database)|indexes]]
* clusters
* database links
* [[Snapshot (computer storage)|snapshot]]s
* [[stored procedure|procedure]]s
* functions
* packages

On the other hand, non-schema objects may include:<ref>{{cite book
|first1= Lance
|last1= Ashdown
|first2= Tom
|last2= Kyte
|others= et al.
|title= Oracle Database Concepts 11g Release 2 (11.2)
|url= http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/tablecls.htm#CNCPT111
|access-date= 2010-04-14
|date= February 2010
|publisher= Oracle Corporation
|quote= Other types of objects are also stored in the database and can be created and manipulated with SQL statements but are not contained in a schema. These objects include database users, roles, contexts, and directory objects.
|archive-url= https://web.archive.org/web/20100129054802/http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/tablecls.htm#CNCPT111
|archive-date= January 29, 2010
|url-status= dead
}}</ref>

* users
* roles
* contexts
* directory objects

Schema objects do not have a one-to-one correspondence to physical files on disk that store their information. However, [[Oracle database]]s store schema objects logically within a [[tablespace]] of the database. The data of each object is physically contained in one or more of the tablespace's [[datafile]]s. For some objects (such as tables, indexes, and clusters) a [[database administrator]] can specify how much disk space the Oracle [[RDBMS]] allocates for the object within the tablespace's datafiles.

There is no necessary relationship between schemas and tablespaces: a tablespace can contain objects from different schemas, and the objects for a single schema can reside in different tablespaces. Oracle database specificity does, however, enforce platform recognition of nonhomogenized sequence differentials, which is considered a crucial limiting factor in virtualized applications.<ref>{{cite journal |last1=McDougall |first1=R |title=Virtualization performance: perspectives and challenges ahead |journal=ACM SIGOPS Operating Systems Review |date=2010 |volume=44 |issue=4|doi=10.1145/1899928.1899933 |s2cid=16112550 }}</ref>