Английский для пользователей компьютеров. Ч.2. Белобородова М.Л - 26 стр.

database.
DBMS software often uses a query language as an interface between the user
and the system. This interface allows users to easily ask questions of the
DBMS and obtain information to answer the questions and produce reports.
DBMS software also includes capabilities to simplify report writing and
maintain the database (utilities) as well as to allow different applications
programs to use the database (DML). During the design of the database, a data
dictionary is constructed that contains all the data descriptions used by the
DBMS to locate and retrieve data. The DBMS also can include a transaction
log of current activity. This log can be used to update necessary backup copies
of the database in case of failure of or damage to the operating database
system.
A DBMS is usually modeled after one of three structures; (1) hierarchical, (2)
network, or (3) relational. These models differ in terms of the cost of
implementation, speed, degree of data redundancy, ease with which they can
satisfy information requirements, and ease with which they can be updated.
The hierarchical database model resembles a family tree; the records are
organized in a one-to-many relationship, meaning that one parent record
can have many child records. Records are retrieved from a hierarchical
model by starting at the root record at the top and moving down through
the structure. There is no connection between separate branches.
The network database model is similar to the hierarchical model, but it
allows multiple one-to-many relationships (each child can have more than
one parent) and relationships between records in different groups. Also,
access to the database can be made from a number of points — not just
from the top.
The relational database model is made up of many tables, called relations,
in which related data elements are stored. The data elements are in rows,
called tuples, and columns, called attributes. The main objective of the
relational database model is to allow complex logical relationships between
records to be expressed in a simple fashion.
    In general, the hierarchical and network models are less expensive to
implement and allow faster access to data. However, they are more difficult to
update and aren't as effective at satisfying information requirements as the
relational model can be. Because the hierarchical and network models are older
than the relational model, they are used most often on large computers. The
newer relational model is used extensively on microcomputers; however,
because relational models are so flexible in satisfying information requests, and
because they aren't difficult to update, relational models are being used more
and more on large computers.
The process of database design is usually carried out exclusively by specialists;
however, users may have occasion to set up small databases for
microcomputers. First, the logical design is set up; then the physical design.
The logical design, which has to do with what the database is, from the