Microsoft Office Tutorials and References
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Relational Database Management Systems
Relational Database Management Systems
To manage its databases, a company purchases a database management system. A
database management system (DBMS) is a software program that lets you create
databases and then manipulate data in them. Most of today’s database management systems,
including Access, are called relational database management systems. In a relational
database management system , data is organized as a collection of tables. As stated
earlier, a relationship between two tables in a relational DBMS is formed through a
common fi eld.
A relational DBMS controls the storage of databases on disk and facilitates the
creation, manipulation, and reporting of data, as illustrated in Figure 1-3. Specifi cally, a
relational DBMS provides the following functions:
• It allows you to create database structures containing fi elds, tables, and table
relationships.
• It lets you easily add new records, change fi eld values in existing records, and delete
records.
• It contains a built-in query language, which lets you obtain immediate answers to the
questions you ask about your data.
• It contains a built-in report generator, which lets you produce professional-looking,
formatted reports from your data.
• It protects databases through security, control, and recovery facilities.
Figure 1-3
Relational database management system
disk storage
database
store, retrieve, and protect data
computer memory
relational DBMS
query
displays
hard copy
reports
user
interaction
with the
database
users
printer
A company such as Belmont Landscapes benefi ts from a relational DBMS because
it allows users working in different groups to share the same data. More than one user
can enter data into a database, and more than one user can retrieve and analyze data
that other users entered. For example, the database for Belmont Landscapes will contain
only one copy of the Contract table, and all employees will use it to meet their specifi c
requests for contract information.
Finally, unlike other software programs, such as spreadsheet programs, a DBMS can
handle massive amounts of data and can be used to create relationships among
multiple tables. Each Access database, for example, can be up to two gigabytes in size,
can contain up to 32,768 objects (tables, queries, forms, and so on), and can have
up to 255 people using the database at the same time. For instructional purposes, the
databases you will create and work with throughout this text contain a relatively small
number of records compared to databases you would encounter outside the classroom,
which likely contain tables with very large numbers of records.
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