Fourth-Generation Languages (4GLs)
There is no consensus about what constitutes a fourth-generation language; it is in
essence a shorthand programming language. An operation that requires hundreds of lines
in a third-generation language (3GL), such as COBOL, generally requires significantly
fewer lines in a 4GL.
Compared with a 3GL, which is procedural, a 4GL is non-procedural: the user defines
what is to be done, not how. A 4GL is expected to rely largely on much higher-level
components known as fourth-generation tools. The user does not define the steps that a
program needs to perform a task, but instead defines parameters for the tools that use them
to generate an application program. It is claimed that 4GLs can improve productivity by
a factor of ten, at the cost of limiting the types of problem that can be tackled. Fourthgeneration
languages encompass:
n presentation languages, such as query languages and report generators;
n speciality languages, such as spreadsheets and database languages;
n application generators that define, insert, update, and retrieve data from the database to
build applications;
n very high-level languages that are used to generate application code.
SQL and QBE, mentioned above, are examples of 4GLs. We now briefly discuss some of
the other types of 4GL.
Forms generators
A forms generator is an interactive facility for rapidly creating data input and display layouts
for screen forms. The forms generator allows the user to define what the screen is to
look like, what information is to be displayed, and where on the screen it is to be displayed.
It may also allow the definition of colors for screen elements and other characteristics,
such as bold, underline, blinking, reverse video, and so on. The better forms generators
allow the creation of derived attributes, perhaps using arithmetic operators or aggregates,
and the specification of validation checks for data input.
Report generators
A report generator is a facility for creating reports from data stored in the database. It is
similar to a query language in that it allows the user to ask questions of the database and
retrieve information from it for a report. However, in the case of a report generator, we
have much greater control over what the output looks like. We can let the report generator
automatically determine how the output should look or we can create our own customized
output reports using special report-generator command instructions.
There are two main types of report generator: language-oriented and visually oriented.
In the first case, we enter a command in a sublanguage to define what data is to be included
in the report and how the report is to be laid out. In the second case, we use a facility
similar to a forms generator to define the same information.
Graphics generators
A graphics generator is a facility to retrieve data from the database and display the data
as a graph showing trends and relationships in the data. Typically, it allows the user to
create bar charts, pie charts, line charts, scatter charts, and so on.
Application generators
An application generator is a facility for producing a program that interfaces with the database.
The use of an application generator can reduce the time it takes to design an entire
software application. Application generators typically consist of pre-written modules that
comprise fundamental functions that most programs use. These modules, usually written
in a high-level language, constitute a ‘library’ of functions to choose from. The user
specifies what the program is supposed to do; the application generator determines how to
perform the tasks.
There is no consensus about what constitutes a fourth-generation language; it is in
essence a shorthand programming language. An operation that requires hundreds of lines
in a third-generation language (3GL), such as COBOL, generally requires significantly
fewer lines in a 4GL.
Compared with a 3GL, which is procedural, a 4GL is non-procedural: the user defines
what is to be done, not how. A 4GL is expected to rely largely on much higher-level
components known as fourth-generation tools. The user does not define the steps that a
program needs to perform a task, but instead defines parameters for the tools that use them
to generate an application program. It is claimed that 4GLs can improve productivity by
a factor of ten, at the cost of limiting the types of problem that can be tackled. Fourthgeneration
languages encompass:
n presentation languages, such as query languages and report generators;
n speciality languages, such as spreadsheets and database languages;
n application generators that define, insert, update, and retrieve data from the database to
build applications;
n very high-level languages that are used to generate application code.
SQL and QBE, mentioned above, are examples of 4GLs. We now briefly discuss some of
the other types of 4GL.
Forms generators
A forms generator is an interactive facility for rapidly creating data input and display layouts
for screen forms. The forms generator allows the user to define what the screen is to
look like, what information is to be displayed, and where on the screen it is to be displayed.
It may also allow the definition of colors for screen elements and other characteristics,
such as bold, underline, blinking, reverse video, and so on. The better forms generators
allow the creation of derived attributes, perhaps using arithmetic operators or aggregates,
and the specification of validation checks for data input.
Report generators
A report generator is a facility for creating reports from data stored in the database. It is
similar to a query language in that it allows the user to ask questions of the database and
retrieve information from it for a report. However, in the case of a report generator, we
have much greater control over what the output looks like. We can let the report generator
automatically determine how the output should look or we can create our own customized
output reports using special report-generator command instructions.
There are two main types of report generator: language-oriented and visually oriented.
In the first case, we enter a command in a sublanguage to define what data is to be included
in the report and how the report is to be laid out. In the second case, we use a facility
similar to a forms generator to define the same information.
Graphics generators
A graphics generator is a facility to retrieve data from the database and display the data
as a graph showing trends and relationships in the data. Typically, it allows the user to
create bar charts, pie charts, line charts, scatter charts, and so on.
Application generators
An application generator is a facility for producing a program that interfaces with the database.
The use of an application generator can reduce the time it takes to design an entire
software application. Application generators typically consist of pre-written modules that
comprise fundamental functions that most programs use. These modules, usually written
in a high-level language, constitute a ‘library’ of functions to choose from. The user
specifies what the program is supposed to do; the application generator determines how to
perform the tasks.
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