Chapter 8 The Tower of Babel

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Chapter 8The Tower of Babel

• Procedural languages
• Special purpose languages
• Alternative language paradigms

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Procedural languages
Special purpose languages

• SQL
• Perl
• HTML

Paradigms

• Fortran
• COBOL
• Pascal
• C/C
• Ada

• Procedural paradigm
• Functional paradigm
• Logic paradigm

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• Java is not the only HLL.
• Each programming language meets specific needs.
• Analogy to cars.
• We could use Java to write engineering
  applications but it was not designed for that.
• Example (2.84)1.8 (use Fortran)
• Sales report use COBOL

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Procedural languages/ Imperative languages

• A program in procedural language consists of
  sequences of statements that manipulate data
  items that is they change the contents of memory
  cells.
• These are called imperative commands
• They follow the fetch/decode/execute cycle of the
  Von Neumann machine.
• The fundamental operations are storing and
  retrieving values.
• Eg. c1 a b-c
• Examples of procedural languages are Fortran,
  COBOL, Pascal, C/C and Ada.
• Syntax differs in languages but they all follow
  the same principle.

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FORTRAN

• FORmula TRANslation.
• Good for scientific computation and engineering
  applications.
• In Java we say
• Number lt 0
• In Fortran we say
• NUMBER .LT. 0
• Fortran requires variable identifiers to be
  uppercase.
• Used jumps to simulate while loops in earlier
  versions.
• GO TO was used (similar to assembly code jump)
• Use of GOTOs is discouraged results in
  spaghetti code.
• Difficult to debug and fix errors.

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COBOL

• COmmon Business Oriented Language
• Good for business needs like payroll, inventory.
• In business applications we have a master file
  and transaction files.
• Eg. an master inventory file contains names,
  manufacturers and qty for various items of the
  inventory.The master file is updated from
  transaction file daily or weekly.
• COBOL is very good at handling file input rather
  than keyboard input.
• Used for producing reports. Does this
  efficiently.
• COBOL uses very English like statements
• Eg. sum ab would be written as
• ADD A to B GIVING SUM
• COBOL is less formula oriented than FORTRAN since
  it is not a scientific computing language.
• COBOL programs needed to be fixed for the Y2K.
• Read page 398 for a description of the Year 2000
  problem.

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PASCAL

• Good language to learn programming.
• Easy to read and learn syntax.
• Not very cryptic like C/C
• There was an object oriented Pascal created by
  Borland called Delphi.
• Eg of PASCAL code
• IF (A lt 6) and (B gt 10) then
• writeln(yes)
• Else
• writeln(no)

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C/C

• C was developed by ATT Bell labs.
• Designed for writing OS and writing system
  software.
• C is efficient.
• Makes use of low level info such as where data is
  stored in memory.
• So C can shield the programmer or allow direct
  access to hardware.
• C allows access to a memory cell address as well
  as to its content.
• To see the address of the memory at which the
  value of an identifier is stored it puts an
  ampersand before the identifier.
• E.g. Lets say you define a variable Number. Just
  saying number will give you value of number but
  if you say number it will give you the address
  of memory location at which number is located.
• C has also a data type called pointer.
• Variables of pointer type contain memory
  addresses instead of the values of the variables.
• Eg. int intPointer
• The above will declare intPointer as a pointer
  variable that will contain the address of a
  memory cell containing integer data.
• Eg. intPointer (int) 800
• Assigns memory address 800 as the value of
  intPointer.

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• C was also developed at ATT Bell labs a decade
  after C was developed.
• C is a subset of C
• C is able to do object oriented programming.
• C code is very similar to Java

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Ada

• Lady Ada Lovelace together with Charles Babbage
  worked on the Analytic Engine
• Ada was regarded as the first programmer.
• http//www.adahome.com/

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Special purpose languages

• SQL Structured Query Language
• Used with databases
• A database is a collection of related facts and
  information.
• Querying a database is important.
• SQL helps to query a database.
• A database has tables and each table has rows and
  columns.
• Example of SQL query
• SELECT NAME
• FROM EMPLOYEE
• WHERE BDATE 02/04/1956

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Special purpose languages

• PERL
• Practical Extraction and Report Language
• Designed to scan arbitrary text files, extract
  various kinds of information that is contained
  within the text, and print reports based on the
  extracted informaitoan.
• Based on C syntax.
• Has good pattern matching techniques.
• Good for web page scripting.

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HTML

• HyperText Markup Language
• You can write web pages using this.
• And you can view it in a internet browser i.e.
  internet explorer or netscape.
• HTML is made up of tags.
• Overall format is something like this
• lthtmlgt
• ltheadgt
• lttitlegt Title of web page goes here lt/titlegt
• lt/headgt
• ltbodygt
• lt/bodygt
• lt/htmlgt

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Procedural paradigm

• A paradigm is a model for representing a
  programming method of thinking.
• Procedural paradigm says that a sequence of
  detailed instructions is provided to the
  computer.
• Each instruction is concerned with accessing and
  modifying contents of memory locations.
• A procedural paradigm consists of
• Plan the algorithm
• Convert the unambiguous and effectively
  computable operations as program instructions.
• Remember that in OOP, this procedural paradigm
  still works.
• Next we will look at other types of paradigms.

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Functional programming paradigm

• LISP is a functional programming language.
• Scheme is another.
• A functional programming language views all tasks
  in terms of functions.
• Certain functions are called primitives.
• Other functions are defined by the programmer.
• Eg.
• (define (double x)
• ( 2 x))
• The function name is double and x is the
  parameter. If we call this function as in (double
  4) what should it output?
• This is the way complex functions are defined.
• LISP is another very powerful language that does
  list processing.
• Eg.
• (list 1 2 4)
• (Car (list 1 2 4)) gives 1
• (Cdr (list 1 2 4)) gives (2 4)
• This type of programming is good for recursive
  modules. Something that is defined in terms of
  smaller versions of itself. Think of how
  factorial is calculated. What about fibonacci
  numbers?

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Functional programming paradigm

• Recursion is one of the features of functional
  programming languages.
• Procedural languages also support recursion
• The main benefit of functional paradigm
• Clarity of thought
• Free flowing data values
• No need to worry about intermediate results or
  how many cells of memory a list would occupy.
• This is another layer of abstraction.
• There are no side effects in functional
  programming. What is a side effect?
• If you overwrite a variable you have caused a
  side effect.
• Impertive/procedural languages have side effects
  by their definition.

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Logic programming paradigm

• Functional programming specifies various
  transformations of data
• Logic programming does not specify how a task is
  to be done. It just says what is to be done.
• In logic programming you define some facts to be
  true.
• On the basis of these facts, a logic program can
  infer or deduce other facts.
• When a query/question is posed to the program, it
  attempts to apply the logical deductions it can,
  to answer the query.
• Also called declarative languages.
• Used to write expert system software.
• Deals a little with artificial intelligence.
• Prolog is an example of a logic programming
  language.

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Prolog

• Prolog programs consist of facts and rules.
• A fact expresses a property about a single object
  or relationship among several objects.
• Consider the following prolog code.
• President(lincoln, gettysburg_address)
• President(lincoln, civil_war)
• President(nixon, first_moon_landing)
• President(jefferson, lewis_and_clark)
• President(kennedy, cuban_missile_crisis)
• President(fdr, world_war_II)
• before(jefferson, lincoln)
• Before(lincoln,fdr)
• Before(fdr, kennedy)
• Before(kennedy, nixon)

• Now if the user enters
• ?-before(lincoln, fdr)
• Prolog will reply yes.
• What about this?
• ?-president(lincoln,x)
• Prolog will reply the following
• Xgettysburg_address
• Xcivil_war

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The logic programming paradigm in a nutshell.
rules
facts
Knowledge Base
Inference engine
query
response
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• End of chapter 8