Databases and applications commonly carry out the function that is illustrated in the graphic that follows. Which of the following best describes the concept that this graphic is showing?

A.
Checkpoint

B.
Commit

C.
Two-phase commit

D.
Data dictionary

Explanation:
A: A checkpoint is used to recover data if there is a system failure or problem during a transaction. It is used to periodically save the state of the application and the user’s
information. It is used so that if the application endures a glitch, it has the necessary tools to bring the user back to his working environment without losing any data. You can
experience this with a word processor when it asks you if you want to review the recovered version of a file you were working on. The word processor has saved your document as you
have worked on it and is able to bring it back in case the system runs into trouble.
B is incorrect because a commit operation completes a transaction and executes all changes just made by the user. As its name indicates, once the commit command is executed,
the changes are committed and reflected in the database. These changes can be made to data or schema information. When these changes are committed, they are then available to
all other applications and users. If a user attempts to commit a change and it cannot complete correctly, a rollback is performed. This ensures that partial changes do not take place
and that data is not corrupted.
C is incorrect because a two-phase commit mechanism is a control that is used in databases to ensure the integrity of the data held within the database. Databases commonly carry
out transaction processes, which means the user and the database interact at the same time. The databases need to make sure each database is properly modified, or no modification
takes place at all. When a database change is submitted by the user, the different databases initially store these changes temporarily. A transaction monitor will then send out a
“precommit” command to each database. If all the right databases respond with an acknowledgment, then the monitor sends out a “commit” command to each database. This ensures
that all of the necessary information is stored in all the right places at the right time.
D is incorrect because a data dictionary is a central collection of data element definitions, schema objects, and reference keys for a database. The schema objects can contain
tables, views, indexes, procedures, functions, and triggers. A data dictionary can also contain the default values for columns, integrity information, the names of users, the privileges
and roles for users, and auditing information. It is a tool used to centrally manage parts of a database by controlling data about the data (referred to as metadata) within the database. It
provides a cross-reference between groups of data elements and the databases.