1. Data Integrity Integrity without knowledge is weak and useless, and knowledge without integrity is dangerous Samuel Johnson, 1759

2. Management of organizational memories

6. ACID Committed data are saved by the DBMS so that, in the event of a failure and system recovery, these data are available in their correct state Durability A transaction in process and not yet committed must remain isolated from any other transaction Isolation A transaction either creates a valid new database state, or, if any failure occurs, the transaction manager returns the database to its prior state Consistency If a transaction has two or more discrete pieces of information, either all of the pieces are committed or none are Atomicity

10. Database update process D a t a b a s e ( s t a t e 1 ) D a t a b a s e ( s t a t e 2 ) D a t a b a s e ( s t a t e 3 ) D a t a b a s e ( s t a t e 4 ) D a t a b a s e ( s t a t e 2 ) U p d a t e t r a n s a c t i o n A U p d a t e t r a n s a c t i o n B U p d a t e t r a n s a c t i o n C

11. Backup options Transaction log or journal Transactions that caused a change in the state of the database Before image log or journal After image log or journal Changes to the database Database backup Past states of the database (also known as database dumps) Dual recording of data (mirroring) Complete copy of database Action Objective

14. Data recovery * preferred strategy *Backward recovery Reprocess transactions (Excluding those from the update program that created incorrect data) Incorrect data detected (database has been incorrectly updated) *Backward recovery Forward recovery or reprocess transactions—bring forward to the state just before termination of the transaction Abnormal termination of an update transaction (transaction error or system failure) *Switch to duplicate database—this can be transparent with RAID Forward recovery Reprocess transactions Storage medium destruction (database is unreadable) Recovery Procedures Problem

18. Integrity constraints Supplier number is unique. Indicating whether stored values for this data item must be unique (unique compared to other values of the item within the same table or record type). The unique option is also required for identifiers. UNIQUE Employee number is mandatory. Indicating whether the data item value is mandatory (not null) or optional. The not null option is required for primary keys. NOT NULL (MANDATORY) If item type is ‘Y’, then color is null. Providing one or more conditions to apply against data values. CONDITIONAL A delivery must have valid itemname, department, and supplier values before it can be added to the database. (Tables are checked for valid entries.) Providing a procedure to be invoked to validate data items. PROCEDURE Department phone number must be of the form 542-nnnn (stands for exactly four decimal digits). Providing a pattern of allowable characters which define permissible formats for data values. PATTERN Employee numbers must be in the range 1-100. Providing one or more ranges within which the data item must fall or must NOT fall. RANGE Item colors must match the list provided. Providing a list of acceptable values for a data item. VALUES Delivery number must be at least 3 digits and at most 5. Defining and validating the minimum and maximum size of a data item. SIZE Supplier number is numeric. Validating a data item value against a specified data type. TYPE Example Explanation Type of constraint

19. Integrity constraints Column stkcode must always be assigned a value of 3 or less alphanumeric characters. stkcode must be unique because it is a primary key. Column natcode must be assigned a value of 3 or less alphanumeric characters and must exist as the primary key of nation. Do not allow the deletion of a row in nation while there still exist rows in stock containing the corresponding value of natcode . CREATE TABLE stock ( stkcode CHAR(3), … , natcode CHAR(3), PRIMARY KEY(stkcode), CONSTRAINT fk_stock_nation FOREIGN KEY (natcode) REFERENCES nation ON DELETE RESRICT); Explanation Example

20. A general model of data security

24. Public key encryption Decrypt Encrypt Receiver’s public key Receiver’s private key Sender Receiver