The main components of security are confidentiality, integrity and availability . Confidentiality is the assurance that information can only be accessed by the intended and authorized recipients. Access control mechanisms can be used to preserve confidentiality. Cryptography can for example be used to make the information unreadable to anyone except the parties who hold the cryptographic key to unscramble the data. Integrity is the assurance to an entity that data has not been altered (intentionally or unintentionally) during transmission, from origin to destination. Integrity mechanisms can be divided into two classes: prevention and detection mechanisms. Prevention mechanisms seek to maintain integrity by thwarting any unauthorised attempts to modify the data, while the purpose of detection mechanisms is to signal if the data’s integrity is breached. The main components of security are confidentiality, integrity and availability . Confidentiality is the assurance that information can only be accessed by the intended and authorized recipients. Access control mechanisms can be used to preserve confidentiality. Cryptography can for example be used to make the information unreadable to anyone except the parties who hold the cryptographic key to unscramble the data. Integrity is the assurance to an entity that data has not been altered (intentionally or unintentionally) during transmission, from origin to destination. Integrity mechanisms can be divided into two classes: prevention and detection mechanisms. Prevention mechanisms seek to maintain integrity by thwarting any unauthorised attempts to modify the data, while the purpose of detection mechanisms is to signal if the data’s integrity is breached. In a distributed database system, a program often referred to as the database's "back end" runs constantly on a server, interpreting data files on the server as a standard relational database. Programs on client computers allow users to manipulate that data, using tables, columns, rows, and fields. To do this, client programs send SQL statements to the server. The server then processes these statements and returns replies to the client program.