ch1 language processors

8/13/2019 Ch1 Language Processors

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Language processors


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PL domain

Three consequences of semantic gap are in

fact consequences of a specification gap.

Large development time

Large development effort

Poor software quality

Solution

Develop PL such that PL domain is very close or

identical to application domain.


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PL domain

Such PLs can only be used for specific applications,hence they are called problem oriented language

They have large execution gap, however this isacceptable because gap id bridge by the translator orinterpreter and does not concern with softwaredeveloper


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PL domain

Procedure oriented languageprovides general

purpose facilities required in most application

domains.

Such a language independent of specific

application domain and results in large

specification gapwhich has to be bridged by a

application designer.


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Language processing activities

The fundamental language processing

activities can be divided into those thatbridge

the specification gap and those that bridge

execution gap.

The activities are

Program generation activities aims -> automatic

generation of program

Program execution activitiesorganize execution

of program written in PL on a computer system


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Program generation

The program generation activities are shownas

The program generator is a software which

accepts the specification of a program to begenerated and generates a program written intarget PL.


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Program generation: Example

Screen handling program

Errors in the specification e.g. invalid start or end

positions or conflicting specifications for a field, aredetected by the generator.

The generated screen handling program validates thedata during data entry, e.g. age field must be only

contains digits.


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Program generation

This arrangements also reduce testing efforts

To test an application generated by using the

generator, it is necessary to only verify

correctness of the specification of input to

the program generator.

This is much simpler task than verifying

correctness of the generated program


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Program execution activities

Two models for program execution

Translation

Interpreter


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Program translation

It bridges the execution gap by translating a

program written in a PL, called source program

(SP), into an equivalent program in the machine orassembly of the computer system called the target

program(TP)


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Characteristics of the Program translation

models are:

A program must be translated before it can be

executed

The translated program may be saved in a file.

The saved program may be executed repeatedly

A program must be translated followingmodification.


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Program interpreter An interpreter is a LP which bridges an execution gap without

generating a machine language program.

The absence of target program implies the absence of anoutput interface of interpreter.

Thus the language processing activities of an interpreter can notseparated from its program execution activities, hence we saythat interpreter executes program written in a PL.


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Program interpreter

During interpretation, it takes a source statement,

determines its meaning and performs actions

which implements it.

This include computational and input-output

actions.


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Characteristics of Program interpretation

The source program is retained in the source

from itself, i.e. no target program from exists.

A statement is analyzed during its interpretation


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Comparison

Translation vs interpreter


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Fundamental processing of Language

Language processing:=

Analysis of SP + Synthesis of TP

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