4.3.6 Database management systems

• Database management system (DBMS)


  The software hosting a database and with which users and other applications interact
• The DBMS is often just called 'a database'
• A relatively small number of companies dominate the market for DBMSs, each with their own designs and functionality, although they share most of the same fundamental principles
• Databases designed in one DBMS are not easily ported to another DBMS, but they can be made to interoperate, either by making one DBMS compatible with another or by supporting industrial standards such as the SQL language
• Standards


  Tightly-defined descriptions of how a product should be constructed or operate
• Most DBMS providers do not exactly conform to the SQL standard, so different implementations of SQL may be incompatible with one another
• Legacy systems


  Old but still highly-useful databases
• The risk of legacy systems lies largely in that they often run on obsolete computer systems, or that the company that wrote the DBMS has either stopped all development and support of the software or has ceased trading entirely