A database server is a server which houses a database application that provides database services to other computer programs or to computers, as defined by the client–server model. Database management systems (DBMS's) frequently provide database-server functionality, and some database management systems (such as MySQL) rely exclusively on the client–server model for database access (while others e.g. Sq-lite are meant for using as an embedded database). Examples of proprietary database applications include Oracle, DB2, Informix, and Microsoft SQL Server. Examples of free software database applications include PostgreSQL; and under the GNU General Public Licence include Ingres and MySQL. Every server uses its own query logic and structure. The SQL (Structured Query Language) query language is more or less the same on all relational database applications. For clarification, a database server is simply a server that maintains services related to clients via database applications.