View n A single table derived from other tables which can be a base table or previously defined views n Virtual table: doesn’t exist physically n Limitation on Update Operations n Advantages: – Facilitate Retrieval Operations (always up- to-date) – Simply query specifications – Security Mechanism

View & SQL View & SQL n CREATE VIEW view_name AS SELECT statements; AS SELECT statements; n CREATE VIEW view_name (attributs) AS SELECT statements; AS SELECT statements; n DROP VIEW view_name; n Query on Views: same as on base tables n DBMS responsibility for keeping views updated;

View Update n A view with a single base table is updatable – primary key or candidate key of the base table must be a view attribute n Views on multiple tables using joins are not updatable n Views defined using grouping and aggregate functions are not updatable n Efficient implementation: – Query modification: – View Materialization : physically create a view table

DBS Security Problems n Physical Safety n Unauthorized Access Of Information n Malicious Alterations n Destruction Of Information n Interception Of Data Transmission n Malicious Software

DBS Security Measures n Physical Security n Discretionary Access Control (Dac) n Mandatory Access Control (Mac) n Statistical Database Security n Data Encryption n Controlling Viruses And Trojan Horses

Physical Security Measures n Penetration Alarm System n Physical Constructions And Barriers n Clear Spaces n Motion Detectors n Controlled Areas n Closed Circuit TV n Physical Personal Id System n Guard And Patrol n Emergency Response Team

Discretionary Access Control n Create user accounts, then grant or revoke privileges to users to access data in a specific mode (read, write, or update) n DB audit n Two level privileges: –account level – relation level: select, modify & reference n Access Matrix model –rows: subjects( users, accounts, programs) –column: objects (relations, views, t, col, operations)

Mandatory Access Control n Based on security classes n Security Classification (classes) Assignment: n Top Secret, Secret, Confidential, Unclassified n multilevel securities - combined with DAC n Bell-laPadula model: class (S), class (O) –read: class (S) >= class(O) –read: class (S) >= class(O) –write: class (S) –write: class (S) n Classification attribute & multilevel relation

Statistical DB Security n Protect the privacy of individual Information by disallowing retrieval of individual data, but allow statistical queries, Like Min. Max, Average,.. n Problem==> possible to deduce the individual information through a sequence of statistical queries –no statistical queries are permitted whenever the number of tuples in the population specified by the selection condition falls below some threshold –prohibit sequences of queries referring repeatedly to the same population –noise