SQL Server 2005 supports several basic security principals located at different levels:

* Windows-Level Principals: Windows Local Login and Windows Network Domain Login - Used to control accesses to SQL Server instances.

* SQL Server-Level Principal: SQL Server Login. - Used to control accesses to SQL Server instances.

* Database-Level Principal: Database User. - Used to control accesses to database instances.

To access a SQL Server instance, you must use a Windows login or a SQL Server login previously created in that server instance. Once you logged in, you are represented by this login name as your security principal at the server level.

If you select a specific database in the server to use, SQL Server will search that database for a previously user that has been mapped to your login name. If that user is located, you are represented by this user name as your security principal at the database level.