Concepts of Database Management, Fifth Edition Chapter 7: DBMS Functions.
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Transcript of Concepts of Database Management, Fifth Edition Chapter 7: DBMS Functions.
Concepts of Database Concepts of Database Management, Fifth Management, Fifth
EditionEdition
Chapter 7:Chapter 7:
DBMS FunctionsDBMS Functions
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Objectives
Introduce the functions, or services, provided by a DBMS
Describe how a DBMS handles updating and retrieving data
Examine the catalog features of a DBMS
Illustrate the concurrent update problem and describe how a DBMS handles this problem
Explain the data recovery process in a database environment
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Objectives
Describe the security services provided by a DBMS
Examine the data integrity features provided by a DBMS
Discuss the extent to which a DBMS achieves data independence
Define and describe data replication
Present the utility services provided by a DBMS
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Nine Functions of a DBMS
Update and retrieve data Provide catalog services Support concurrent update Recover data Provide security services Provide data integrity features Support data independence Support data replication Provide utility services
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Update and Retrieve Data
Fundamental capability of a DBMS
Users don’t need to know how data is stored or manipulated
Users add, change, and delete records during updates
Users view and manipulate data during retrieval
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Figure 7.1: Adding Record
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Figure 7.2:Updating Record
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Figure 7.3: Retrieving Data
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Provide Catalog Services
Stores data about data
Contains descriptions of database components
Often hidden from users
Used by database administrators and programmers
Data dictionary in larger DBMSs
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Support Concurrent Update
Ensures accuracy when several users update database at same time
Manages complex scenarios for updates
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Figure 7.4: Ryan Updates the Database
Before update
DBMS reads data from database into RAM for Ryan
Ryan changes data in RAM
DBMS updates database with Ryan’s change
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Figure 7.5: Elena Updates the Database
After Ryan’s update and before Elena’s
DBMS reads database data into RAM for Elena
Elena changes data in RAM
DBMS updates database with Elena’s change
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Figure 7.6a: Lost Update
Database before updates
Ryan changes data in RAM
DBMS reads database data into RAM for Elena
DBMS reads database data into RAM for Ryan
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Figure 7.6b: Lost
Update (con’t.)
Elena updates data in RAM
DBMS updates database with Ryan’s change
DBMS updates database with Elena’s change; Ryan’s update is lost!
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Avoiding Lost Updates
Prohibit shared update
Use batch processing
Implement locking scheme
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Figure 7.7: Delaying Updates
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Figure 7.8a: Locking Scheme
Database before updates
DBMS reads database data into RAM for Ryan and locks record
Elena requests same record and request fails
Ryan changes data in RAM; Elena’s request for same record again fails
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Figure 7.8b: Locking Scheme
(con’t.)
DBMS updates database with Ryan’s change; Elena’s request for same record again fails
DBMS unlocks record; DBMS reads database data into RAM for Elena and locks record
Elena changes data in RAM
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Figure 7.8b: Locking Scheme (con’t.)
DBMS updates database with Elena’s change
DBMS unlocks record
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Locking Schemes Two-Phase Locking
Locks are held until required updates completed Deadlock
Occurs when two users hold a lock and require a lock on the resource that the other already has
DBMS chooses method to break deadlock One user becomes ‘victim’
Locking on PC-Based DBMSs Table or row locked, not both Usually more limited than locking facilities on
mainframe DBMSs
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Locking Schemes (con’t.)
Timestamping
DBMS assigns each database update a unique time when the update started
Avoids the need to lock rows
Eliminates processing time needed to apply and release locks
Helps detect and resolve deadlocks
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Figure 7.9: Deadlock
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Recovery
Mechanism for recovering damaged database
Recovery: return of database to correct state
Simplest recovery involves using backups
Other recovery methods: Journaling
Forward recovery
Backward recovery
PC-based
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Figure 7.12: Forward Recovery
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Figure 7.13:Backward Recovery
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Provide Security Services
Prevention of unauthorized access
Encryption - converts data to indecipherable form
Authentication - identification of DBMS user, often with passwords or biometrics
Authorizations - rules to specify data available to certain users
Views
Privacy
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Provide Data Integrity Features
Rules followed to ensure data is accurately and consistently updated
Key integrity
Foreign key and primary key constraints
Data integrity
Data type
Legal values
Format
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Figure 7.21: Integrity Constraints in a DBMS
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Support Data Independence
Programs must be independent of database structure
Considerations
Adding a field
Changing length of field
Creating an index
Adding or changing a relationship
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Support Data Replication
Manage multiple copies of same data in multiple locations
Maintained for performance or other reasons
Ease of access and portability
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Figure 7.22:Replicas From Master Database
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Figure 7.23:DBMS Synchronizes Databases
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Provide Utility Services
Assist in general database maintenance
Permit changes to database structure
Permit addition and deletion of indexes
Provide access to operating system services
Support for queries, screen generators, and report generators
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Provide Utility Services (con’t.)
Provide support for embedded procedures
Procedural
Nonprocedural
Provide easy-to-use, menu-driven interface
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Summary A DBMS provides update and data retrieval
functions
DBMS catalog service
Support concurrent update
Prevent shared update, locking systems, timestamp updates
Recovery services allow a database to overcome unexpected failures
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Summary Security Services ensure users don’t have access
to data they are not authorized to view, update or delete
Data replication services allow you to maintain copies of the data closer to where you use it or to provide for disaster recovery
Your DBMS will provide a set of utility services, such as reporting and access to operating system services