MBA 664 Database Management Dave Salisbury ( ) (web site)

SDLC and the database development process SDLCDatabase Deliverable Project ID Project init Analysis Logical design Physical design Implementation Maintenance Enterprise model Conceptual Model Logical model Data structures and storage plan Management Working system

Proper delivery of information not only depends on the capabilities of the computer hardware and software but also on the organization’s ability to manage data as an important resource Data as a Resource

How Does IS Manage Data? Data Administrators: A high-level function that is responsible for the overall management of data resources in an organization, including maintaining corporate-wide definitions and standards. Database Administrators: A technical function that is responsible for physical database design and for dealing with technical issues such as security enforcement, database performance, and backup and recovery. Data Stewardship: Manages a specific logical data resource for all business functions. Distribute data admin. to those most knowledgeable about specific data

Data Administration Functions Data policies, procedures, standards Planning Data conflict (ownership) resolution Internal marketing of DA concepts Managing the data repository

Database Administration Functions Selection of hardware and software Managing data security, privacy, and integrity Data backup and recovery Figure 12.1 offers a list of DA and DBA functions

Threats to Data Security Accidental losses attributable to: –Human error. –Software failure. –Hardware failure. Theft and fraud. Improper data access: –Loss of privacy (personal data). –Loss of confidentiality (corporate data). Loss of data integrity. Loss of availability (through, e.g. sabotage).

Data security threat sources

Database Security Features Protection of the database against accidental or intentional loss, destruction or misuse –Views –Authorization rules –User-defined procedures –Encryption procedures –Authentication schemes

Database Security Features Views –Restrict user access to data –Various ways to get around so not sufficient measure Authorization Rules –Controls embedded in DBMS that restrict user access to data and user actions that can be enacted on data Who can update? Insert? Read?

Authorization matrix

Database Security Features User-Defined Procedures –Allows system designers to add other security features Passwords Valid procedure name Encryption –Coding of data so that it cannot be read by humans Financial and military data WWW issues Government ability to decode all encryption schemes

Database Security Features Authentication Schemes –How to positively identify that person trying to gain access to a computer resource is “that” person Biometric devices--measure fingerprints, voice prints, retina prints Smart card would have biometric data embedded

Database Failures Aborted Transactions –A transaction is not completed Incorrect Data –data entry error, calculation error, coding error System Failure –Component failure, power failure Database Destruction –drive failure, disaster recovery

Database Recovery and Basic Recovery Facilities Backup facilities Periodic backup copies of entire DB Journalizing facilities Maintain an audit trail of transactions and DB changes Checkpoint facilities DBMS suspends all processing and synchronizes files and journals Recovery manager Allows the DBMS to restore the DB to correct condition and restart

Recovery and Restart Procedures Restore/Rerun –Reprocess the day’s transactions up to the point of failure against a backup copy of the database –Simple –Time to reprocess may be prohibitive –Sequencing of transactions may be different than when originally run withdrawal posted prior to deposit

Recovery and Restart Procedures Transaction Integrity –Transaction changes are not made to the DB until the entire transaction has been completed and the changes are committed –If transaction fails at any point, the transaction is aborted

Recovery and Restart Procedures Backward Recovery (Rollback) –Back out of unwanted changes to the database –Used to reverse the changes that have been made to transactions that have been aborted Forward Recovery (Rollforward) –Use an earlier copy of the DB and apply after images of good transactions –More accurate and faster than restore/rerun

Basic recovery techniques (a) Rollback

(b) Rollforward

Concurrency Control Concerns with preventing loss of data integrity due to interference between users in a multi-user environment –Pessimistic approach: interference will always occur so we LOCK records –Optimistic approach: interference will rarely occur so we VERSION records Multiple concurrent updates to a database can lead to lost updates and therefore to errors

Lost Update Example Time John Read account Balance (balance = $1,000). Withdraw $200 (balance = $800. Write account balance (balance = $800) Marsha Read account balance (balance = $1,000). Withdraw $300 (balance = $700). Write account balance (balance = $700) ERROR

Locking Deny access of data to other users while an update is underway Locking level (granularity) –Database - during backups –Table - during batch updates –Block or page - generally not used –Record - Often used –Field - Useful when only one field is likely to change

Types of Locks Shared –Allows others to read, but not write –Prevents others from putting Exclusive lock on the record Exclusive –Denies other access to the record (even read) –Necessary when updating the record

Deadlock (aka: Deadly Embrace) Two or more transactions have placed locks on record(s) that the others need. Each waits for the other(s) to release Requires DBMS intervention –Prevention, often not practical –Resolution, common solution Detects deadlock and backs one or more transactions out, lets one finish, then restarts next transaction.

Versioning Each transaction is restricted to a view of the database as of the transaction start time. When transaction modifies a record, the DBMS creates a new version of record instead of overwriting old record Changes to 2 identical views simultaneously –First change (according to time stamp) is enacted –Second change is informed of conflict and transaction must be performed again

Versioning John Read account Balance (balance = $1,000). Withdraw $200 (balance = $800. Commit Marsha Read account balance (balance = $1,000). Attempt to withdraw $300 (Denied - balance update conflict). Rollback Restart transaction

Managing Data Quality Security policy and disaster recovery Personnel controls Physical access controls Maintenance controls (hardware & software) Data protection and privacy