Page 179 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes the file processing system because the independent data files produce duplicate data so when
updates were needed each separate file would need to be updated. Another issue is the lack of data
integration. The data is dependent on other data to organize and store it. Lastly, there was not any
consistency or standardization of the data in a file processing system which makes maintenance
difficult. For these reasons, the database management approach was produced.
8.2.1.3 Data Structure

Data structures (fields, records, files and objects) optimized to deal with very large amounts of
data stored on a permanent data storage device (which implies relatively slow access compared
to volatile main memory).

8.2.1.4 Database Query Language
A database query language and report object allows users to interactively interrogate the database,
analyze its data and update it according to the users’ privileges on data. It also controls the
security of the database. Data security prevents unauthorized users from viewing or updating the
database. Using passwords, users are allowed access to the entire database or subsets of it called
subschemas. For example, an employee database can contain all the data about an individual
employee, but one group of users may be authorized to view only payroll data, while others are
allowed access to only work history and medical data.

If the DBMS provides a way to interactively enter and update the database, as well as interrogate
it, this capability allows for managing personal databases. However, it may not leave an audit trail
of actions or provide the kinds of controls necessary in a multi-user organization. These controls
are only available when a set of application programs are customized for each data entry and
updating function.
8.2.1.5 Transaction Mechanism

A database transaction mechanism ideally guarantees ACID properties in order to ensure data
integrity despite concurrent user accesses (concurrency control), and faults (fault tolerance). It
also maintains the integrity of the data in the database. The DBMS can maintain the integrity of
the database by not allowing more than one user to update the same record at the same time.
The DBMS can help prevent duplicate records via unique index constraints; for example, no two
customers with the same customer numbers (key fields) can be entered into the database. See
ACID properties for more information (Redundancy avoidance).

8.3 Working with Database

Almost all of the most useful sites on the web use databases to organise their content, and
they often use them to allow users to register and leave comments too. Any time you do
something that a website seems to ‘remember’ the next time, the chances are that a database
is involved.
Yet, despite how common databases are, they aren’t very well understood. Every day, new
webmasters become database administrators without even understanding the first thing about
databases. When you use a database on the web today, you’re not just using any database: you’re
using ones that rely on concepts built up over decades of database development and proven
effective. Here are some of those concepts.

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