29-03-2012, 04:16 PM
4th generation programming language
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4th Generation Programming Languages
A fourth-generation programming language (or 4GL) is a programming language designed with a specific purpose in mind such as the development of commercial business software.
fourth-generation languages are closer to human languages than typical high-level programming languages.
Most 4GLs are used to access databases.
History Of 4GL
The term 4GL was according to James Martin first used in his 1982 book Applications Development Without Programmers to refer to non-procedural high-level specification languages.
A SPECIFICATION language is one that enables a programming task to be performed by the construction of a set of non-procedural statements.
Additional Components
Some 4GLs have integrated tools which allow for the easy specification of all the required information.
James Martin's Information Engineering systems development methodology
allow the input of the results of system analysis and design in the form of Data Flow Diagrams, Entity Relationship Diagrams, Entity Life History Diagrams etc from which hundreds of thousands of lines of COBOL would be generated.
Oracle Corporation’s Oracle Designer and Oracle Developer
could be integrated to produce database definitions and the forms and reports programs.
4GL Advantages & Disadvantages
Being specification languages, their use requires, in theory at least, no programming task; the necessary code will be generated directly from the specification.
Can only address a small and very highly specialized area of development
FOURTH GENERATION ENVIRONMENT (4GE)
In order to provide an environment in which a complex system can be developed, a number of different types of "pure" fourth generation languages must be integrated, and further procedural programming facilities must be provided.
SQL Command Types
Query Commands
Select
Create View
…
Update Commands
Insert
Delete
Update
…
Embedded SQL
The SQL standard defines embeddings of SQL in a variety of programming languages such as Pascal, PL/I, Fortran, C, and Cobol.
A language to which SQL queries are embedded is referred to as a host language, and the SQL structures permitted in the host language comprise embedded SQL.
EXEC SQL statement is used to identify embedded SQL request to the preprocessor
EXEC SQL <embedded SQL statement > END-EXEC
Note: this varies by language. E.g. the Java embedding uses # SQL { …. } ;