Securables are the resources to which the SQL Server Database Engine authorization system regulates access. For example, a table is a securable. Some securables can be contained within others, creating nested hierarchies called "scopes" that can themselves be secured. The securable scopes are server, database, and schema.
Securable scope: Server
The server securable scope contains the following securables:
Securable scope: Database
The database securable scope contains the following securables:
Remote Service Binding
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Securable scope: Schema
The schema securable scope contains the following securables:
XML schema collection
Object - The object class has the following members:
Controlling Access to a Securable
The entity that receives permission to a securable is called a principal. The most common principals are logins and database users. Access to securables is controlled by granting or denying permissions, or by adding logins and users to roles which have access. For information about controlling permissions, see GRANT (Transact-SQL), REVOKE (Transact-SQL), DENY (Transact-SQL), sp_addrolemember (Transact-SQL), and sp_droprolemember (Transact-SQL).
The default permissions that are granted to system objects at the time of setup are carefully evaluated against possible threats and need not be altered as part of hardening the SQL Server installation. Any changes to the permissions on the system objects could limit or break the functionality and could potentially leave your SQL Server installation in an unsupported state.