LANGUAGE PROCESSORS

Language processors◦ Language processing activities arise due to the

differences between the manner in which a software designer describes the ideas concerning the behavior of software and the manner in which these ideas are implemented in computer system.

◦ The designer expresses the ideas in terms related to the application domain of the software.

◦ To implement these ideas, their description has to be interpreted in terms related to the execution domain.

Specifications

Introduction

The term semantics to represent the rules of meaning of a domain, and the term semantic gap to represent difference between the semantics of two domains.

Application domain

Execution domain

Semantic gap

Semantic Gap

Reservation Data

Query`

Booking`

Cancellation`

CPU registersMemory

I/O Devices

CPU Instructions

`

Application Domain

Execution Domain

Semantic Gap

Semantic Gap

The semantic gap has many consequences, some of the important are◦ Large development times◦ Large development effort◦ Poor quality software.

these issues are tackled by software engineering thru’ use of methodologies and programming languages.

Semantic Gap

Key Software engineering steps1) Specification and design of an

application program, followed by its coding in a programming language

2) Execution of the program with the help of language processor

Semantic Gap

An Application program written in a programming language is governed by semantics of a programming language.

Thus use of programming language has introduces a new domain, programming language domain PL Domain.

Semantic Gap

Application domain

PL domain

Specification gap

Execution domain

Execution gap

Specification and execution Gap

Specification Gap: Semantic gap between two specification of the same taskExecution Gap:Semantic gap between the semantics of programs that performs the same task but written in different programming languages.

Specification and execution Gap

Reservation DataQuer

yBookingCancellatio

n

CPU registersMemory

I/O Devices

CPU Instructions

Application Domain

Execution

Domain

Data Structure

Functions

Programming LanguageDomain

Execution Gap

Specification Gap

Specification and execution Gap

Problem and procedure oriented programming languages

Problem oriented programming languages Lets a user specify a computation using

data and operation that are meaningful in the area of the computation

Procedure oriented programming languages It provides some standard methods of

creating data and performing operations and lets the user describe the intended computation by using them

A language processor is software which bridge a specification or execution gap.

Language processor abandons generation of target program if it detects error in the source program

Different Types of Language Processors:◦ A Language Translator◦ De-translator◦ Preprocessor◦ Language migrator

Language Processor

Source Program

TargetProgram

Language Processors

Types of Language Processors

Language translator: bridges an execution gap between PL, and the

machine language of a computer.De-translator Bridges the same execution gap as the language

translator but in the opposite directionPreprocessor Bridges an execution gap but is not a language

translatorLanguage Migrator Bridges specification gap between two programming

languages

C++ Program

C++ Preprocess

orC

Program

Errors

C++ Program

C++ Translator

Machine language program

Errors

Example: Preprocessor and Translator

Interpreter domain

An interpreter is language processor which bridges an execution gap without generating a machine language program that means the execution gap vanishes totally.

Application domain

PL domain

Execution domain

Interpreter

Fundamental activities divided into those that bridge the specification gap and execution gap.◦ Program generation activities◦ Program execution activities

◦ A program generation activity aims at automatic generation of a program.

◦ A source language is a specification language of an application domain and the target language is procedure oriented PL.

◦ Program generator introduces a new domain between the application and PL domain , call this the program generator domain.

◦ Specification gap now between Application domain and program generation domain, reduction in the specification gap increases the reliability of the generated program.

Program Generation

Program Generation

Program ExecutionProgram execution

Two popular modelProgram TranslationProgram Interpretation

Program Translation The program translation model bridges the execution

gap by translating a sources program into program in the machine or assembly language of the computer system, called target program.

Characteristics of the program translation model:◦ 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 retranslated following

modifications.

Program Execution

Program Translation

Program Execution

Program interpretation: during interpretation interpreter takes source program statement, determines its meaning and performs actions which implement it.

The function of an interpreter is same as the execution of machine language program by CPU.

Program Interpretation

Program Execution

Characteristics◦ The source program is retained in the source form

itself, no target program form exists,◦ A statement is analyzed during its interpretation.

Comparison◦ In translator whole program is translated into

target and if modified the source program, whole source program is translated irrespective to size of modification.

◦ That not the in case of interpreter, interpretation is slower than execution of m/c language program.