Page 1432 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Databases that fail to implement concurrency correctly may suffer
from the following issues:

Lost updates occur when two different processes make updates

to a database unaware of each other’s activity. For example,
imagine an inventory database in a warehouse with different
receiving stations. The warehouse might currently have 10 copies
of the CISSP Study Guide in stock. If two different receiving
stations each receive a copy of the CISSP Study Guide at the same

time, they both might check the current inventory level, find that it
is 10, increment it by 1, and update the table to read 11, when the
actual value should be 12.

Dirty reads occur when a process reads a record from a
transaction that did not successfully commit. Returning to our
warehouse example, if a receiving station begins to write new
inventory records to the database but then crashes in the middle of

the update, it may leave partially incorrect information in the
database if the transaction is not completely rolled back.

Concurrency uses a “lock” feature to allow one user to make changes
but deny other users access to views or make changes to data elements
at the same time. Then, after the changes have been made, an “unlock”
feature restores the ability of other users to access the data they need.
In some instances, administrators will use concurrency with auditing

mechanisms to track document and/or field changes. When this
recorded data is reviewed, concurrency becomes a detective control.

Other Security Mechanisms

Administrators can deploy several other security mechanisms when
using a DBMS. These features are relatively easy to implement and are
common in the industry. The mechanisms related to semantic
integrity, for instance, are common security features of a DBMS.
Semantic integrity ensures that user actions don’t violate any

structural rules. It also checks that all stored data types are within
valid domain ranges, ensures that only logical values exist, and
confirms that the system complies with any and all uniqueness
constraints.