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e\L-lovely-eng\comm8-1.pmd IInd 16-9-11 IIIrd 22-12-11 IVth 4-1-12

Information and Communication Technology Applications

• They have instructions which can execute any query. Sometimes they are known as query
Notes language also.
• Some 4GLs languages have a report generator which generates the complex reports.
• Some 4GLs have the instructions to develop the graphical user interfaces.
• They are result oriented.
• They emphasize on result (what) rather than method (how).
• They improve productivity because code is easy to write and change.
• As the language is easy, simple, both programmers and non programmers can use them with
a minimum of training.
• Transparency regarding the awareness of shareware and program structure.

8.6 Category of Programming Languages

There are some different sort of constructs which a language provides. There are often minor syntactic
variations that shows the thinking of the language designers and then displays the effect upon the
programms written in those languages. Now we have a look on different basic models that describes
the behaviour of programming languages.

8.6.1 Imperative Languages

• Imperative programming specify everything: Data declarations, state-changing and flow of
control.
• Aliasing binds more than one name to one item, overloading binds one name to more than
one item. When using an overloaded name, the context determines which item it refers to:
The context disambiguates.
• A type is a set of values: Often a set of operators is defined on it and sometimes an allocator
and a destructor is defined for it.
• There are basic types (integer, etc.): More complex types can be made using type constructors.
• There is one type constructor that uss no other types: Enumeration.
• There are three type constructors that can use any number of types: Records, unions and
procedures (routines).
• Records can be recursive through the use of pointers: In almost all languages pointers can also
point to items of other data types.
• A pointer to an item of type T is an independent item of type pointer to T; and operation
called ‘dereference’ is needed to access the item pointed to. A reference to an item of type T is
just an alias for that item; it is of type T and no operation is required to access the item.
• Routines can be a data type in some languages. They can be passd as parameters and as-
signed to routine variables. The only operation on them is the routine call, supplying the
parameters.
• Orthogonality: Two features are orthogonal if any example of the first feature can be freely
and meaningfully combined with any example of the second feature.
• Restricted types: Have a subset of the values of the base type. More operations are allowed on
the subset that on the original set.
• Signals: Asynchronous, usually with external cause. Exceptions: synchronous, with internal
cause.

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