Download DBMS Functions Data, Storage, Retrieval, and Update

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Microsoft SQL Server wikipedia, lookup

Clusterpoint wikipedia, lookup

Open Database Connectivity wikipedia, lookup

Relational model wikipedia, lookup

Database model wikipedia, lookup

Microsoft Jet Database Engine wikipedia, lookup

Concurrency control wikipedia, lookup

Serializability wikipedia, lookup

Versant Object Database wikipedia, lookup

Commitment ordering wikipedia, lookup

Extensible Storage Engine wikipedia, lookup

Functional Database Model wikipedia, lookup

Database wikipedia, lookup

Global serializability wikipedia, lookup

Entity–attribute–value model wikipedia, lookup

ContactPoint wikipedia, lookup

Oracle Database wikipedia, lookup

IMDb wikipedia, lookup

Ingres (database) wikipedia, lookup

Transcript
DBMS Functions
Data, Storage, Retrieval, and Update
• Provides users with the ability to store,
retrieve, and update the data that are in the
database.
DBMS Functions
Shared Update
• Ensures accuracy when several users are
updating the database at the same time.
Avoiding Inconsistent Data
• Prohibit shared update.
• Use batch processing
• Lock other users from accessing records
that are being updated by another.
Concurrency Control
• The DBMS must prevent or overcome
the interference of transactions of
multiple users
• Locking
– different levels of granularity (records to tables)
Avoiding the Problem
• Two-Phase Locking
– Locks are held until all the required updates have been
completed.
• Deadlock
– Occurs when two users hold more than one lock at a
time.
• Locking on PC-Based DBMSs
– Usually much more limited than locking facilities
provided by mainframe DBMSs.
Record Locking
• Deadlock prevention
• Deadlock resolution
Avoiding the Problem
• Timestamping
– The DBMS assigns to each database update the
unique time when the update started, called a
timestamp.
– Avoids the need to lock rows and eliminates the
processing time needed to apply and release
locks; also detects and resolves deadlocks.
Backup and Recovery
• Provides a mechanism for recovering the
database in the event that the database is
damaged in any way.
• The process of returning the database to a
correct state is called recovery.
• Periodically making a copy of the database
is called backup.
Replication
• A way to manage copies of the same data at
multiple locations.
Security
• The protection of the database against
unauthorized access.
– Passwords
– Encryption
– Views
Integrity
• Integrity constraints, or conditions, fall into
four categories:
–
–
–
–
Data type
Legal values
Format
Key constraints
Integrity Constraints in a DBMS
Data Independence
• Facilities that allow programs to be
independent of the structure of the database.
–
–
–
–
Addition of a field
Changing the length of a field
Creating a new index
Adding or changing a relationship
ACID properties
• Atomic
– all of a transaction should be executed or none
• Consistent
– the database should be in a “consistent” state after the
transaction is completed
• Isolated
– Updates of concurrent transactions should be concealed
from each other, till committed
• Durable
– once a transaction commits, its updates survive even if
there is a subsequent system crash