Computer World. Матросова Т.А. - 60 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

59
A relational DBMS (RDBMS) is a software program that supports the relational
model. A definition of a relational database system has been proposed by a Relational
Task Group. Such a definition is useful to characterize systems that are claimed to be
relational. A system is said to be minimally relational if it satisfies three conditions:
1. All information in the database is represented as values in tables.
2. No intertable pointers are visible to the user.
3. The system must support at least the following relational algebra operators:
select, project, and natural join. These operators must not be restricted by internal
constraints. An example of internal constraint that exists in some systems is that there
must exist an index on join attribute to perform a join. These constraints limit the
power of the database language.
TEXT 6
Sum up information about Database Management Systems.
Retell the text.
♦ Database Managemt it Systems: A DBMS is characterized by the ability
to support efficient access to large amounts of data, which persists over
time. It is also characterized by support for powerful query languages and
for durable transactions that can execute concurrently in a manner that
appears atomic and independent of other transactions;
♦ Comparison With File Systems: Conventional file systems are inadequate
as database systems, because they fail to support efficient search, efficient
modifications to small pieces of data, complex queries, controlled buffering
of useful data in main memory, or atomic and independent execution of
transactions;
♦ Relational Database Systems: Today, most database systems are based
on the relational model of data, which organizes information into tables.
SQL is the language most often used in these systems;
♦ Secondary and Tertiary Storage: Large databases are stored on secondary
storage devices, usually disks. The largest databases require tertiary storage
devices, which are several orders of magnitude more capacious than
disks, but also several orders of magnitude slower;
♦ Client-Server Systems: Database management systems usually support a
client-server architecture, with major database components at the server and the
client used to interface with the user;
♦ Future Systems: Major trends in database systems inc lude support for
very large ‘’multimedia” objects such as videos or images and the integration of
information from many separate information sources into a single
database;
♦ Database Languages: There are languages or language components for
defining the structure of data (data-definition languages) and for querying
and modification of the data (data-manipulation languages);
♦ Components of a DBMS: The major components of a database man-

Страницы