schema vs. user；schema vs. database
Schema Vs. User Technically, a schema is a collection of database objects owned by a specific user. Those objects include tables, indexes, views, stored procedures, etc. In Oracle, a schema requires a user to be created. But you can create a user that has no schema (i.e, no objects). So in Oracle, the user is the account and the schema is the objects.
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Schema Vs. User Whenever a new user is created, a schema with the same name as of user is also created. The user owns the schema and all the objects created in his schema. The term 'user' is normally used in context to 'login' and schema is used while refering to database objects e.g. tables, views etc. However, both terms could be used interchangeably and you can consider a user to be schema and vica versa.
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schema vs. database
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Schema Vs Database It seems that schema and database are interchangeable terms with the same meaning in MySQL, is that right? Is this how it is in other RDBMSs, or is MySQL different in this regard? Looking up briefly on other RDBMSs, it seems that they use database to refer to the database (good description, huh? ) and schema to refer to the "owner" of that database? I don't really know what the difference is, and how to define on versus the other. Can somebody explain the difference (better than my "a database is a database"), and why other RDBMSs see a need to do it this way (i.e. what's the benefit of implementing a whole other concept known as schema)? Does MySQL have plans to change things in the future on this issue? Or have I totally misunderstood the concepts of database vs schema, and how MySQL defines it?
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A schema is essentially a logical grouping of SQL objects, like tables, views and stored procedures etc. But it is used very different by different DB's. In Oracle for example you create a DB and in the DB you then create users where each user gets an implicit schema named the same. When you then create tables you do this in a specific schema which means that the names doesn't collide if different users are using the same table name. In Oracle you need to choose which schema you want to work with much like you choose a database in MySQL. The thing is that what makes this very confusing is that Oracle has an extra level of abstraction that doesnt' exist at all in MySQL. You can sort of look at it like this: Oracle: table->schema->database MySQL: table->database Because Oracle and MySQL has a very different view of what is a database. Because a database in MySQL is much more like a schema in Oracle. In Oracle a database is a separate set of data files and a separate set of processes running. While in MySQL it is only one process running. So summary is that schema is a logical grouping of database objects inside a database. Making it possible to have several tables with the same name in the same database.
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Schema vs Database? A database can be described as a collection of structured data that usually are stored in computer systems. The structure for a database is arrived at by properly organizing the data with the help of a database model. The term “schema” means “a plan or a shape” and can be defined as the terminology used to model or create a logical structure using which data can be stored in a database. Technically speaking, a database schema is the underlying structure described by and supported by the database management system that is used to store records. Generally, a schema is a higher level of abstraction of the design models which are captured and documented by database designers and business analysts during the analysis phase of a project or product development. They do not exist as such in a database, but in some variants of databases they can be realized at some levels in a physical form. When we bring a user into this perspective, then we can define these three entities (database, schema, and user) as below: Database is a collection of physical files. A user is one who connects to a database. Schema is the collection of objects which are owned by the user. To sum it up briefly, a schema is usually a graphical representation of the database system’s structure whereas the database itself is a structured collection of records or data. Summary: 1.A database is the physical structure. 2.Schema is the logical structure. 3.A database is a collection of related records and data stored in tables. 4.A schema, on the other hand, is a logical definition of the database or, in other words, a blueprint that defines the names of all the tables and columns and defines what type each column is, etc. 5.In some database management systems, a schema can be realized in a physical form at any of the levels. 6.There is no one-on-one correspondence between schema objects and the physical files which store information on disks. Read more: Difference Between Schema and Database | Difference Between | Schema vs Database http://www.differencebetween.net/technology/software-technology/difference-between-schema-and-database/#ixzz1SdugG4M0
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14 INTRODUCTION TO DATABASE SYSTEM
S 1.8.3 Physical Data Model
Physical data model describes the data in terms of a collection of fi les, indices, and other storage struc
-tures such as record formats, record ordering, and access paths. This model specifi es how the database
will be executed in a particular DBMS software such as Oracle, Sybase, etc., by taking into account
the facilities and constraints of a given database management system. It also describes how the data is
stored on disk and what access methods are available to it.
NOTE An access path (for example , an index) is a structure that helps in effi cient searching
and retrieval of data from a particular database .
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Fig. 1.7 An example of instance - PUBLISHER instance
The schema and instance can be compared with a program written in a programming language.
The database schema is similar to a variable declared along with the type description in a program.
The variable contains a value at a given point of time. This value of a variable corresponds to an
instance of a database schema.
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