Chapter1, Study notes of Food Science and Technology

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COMPUTATIONAL MODELS

Chapter No. 1

What Is Computational

Model?

 The common basis of programming

language and computer architecture

is known as computational model.

 Provides higher level of abstraction

than the programming language and

the architecture.

 Computational model is the

combination of the above two.

What Is Computational

Model? cont’n

What is a computer program?

 (^) It is an executable representation of some algorithm designed to solve some real world problem.  (^) There are thus two elements to a computer program:  (^) Logic - what we what the program to achieve.  (^) Control - how we are going to achieve the end goal. ALGORITHM = LOGIC + CONTROL

Imperative Languages con’t

 Order of execution is crucial, commands

can only be understood in context of

previous computation due to side effects.

 Control is the responsibility of the

programmer.

 E.g ALGOL, Pascal, Ada and C

Functional Languages

 A program in a functional language consists of

a set of (possibly recursive) function definitions

and expression whose value is output as the

program's result.

 Functional languages are one kind of

declarative language.

 Declarative languages allow the programmer

to concentrate on the logic of an algorithm

(declarative languages are goal driven,control

is not the concern of the programmer)

Interpretation of the Concept of

a Computational Model

 (^) The computational model comprises of three sets of abstraction:

Computational Model

Basic Items of Computation Problem Description Model Execution Model

Basic Items of Computation

 This is the specification of the items the

computation refers to the kind

computations (operations) that can be

performed on them.

 E.g of items of computations are:

 data, objects or messages, arguments

and functions, elements of sets and

predicate declared on them.

Problem Description Style

 It specifies how the problems in a

particular computational model are

described.

Style

Procedural

Declarative

Procedural Style

 In a procedural style the algorithm for

solving the problem is stated. A particular

solution is then declared. (Imperative

languages uses procedural style)

int nfac (int n) { int fac = 1; if (n > 0) for ( int i = 2; i <= n; i++ ) fac = fac * i; return fac; }

Declarative Style

 (^) Functional style  (^) relationships are expressed using functions.  (^) E.g. (square (n) ( n n))*  (^) This is a function square,that express the relationship between the input n and the output value nn.  (^) Logic style  (^) relationships are declared using expressions known as clauses.  (^) E.g. square(N, M):- M is NN  (^) Clauses can be used to express both facts and rules.

Problem Description Method

 Procedural style

 (^) the problem description model states how a solution of the given problem has to described.

 Declarative style

 (^) the problem description model states how the problem itself has to be described.

Interpretation of the Execution

 (^) How to perform the computation?  (^) It relates to problem description method  (^) Problem description method and the interpretation of the computation mutually determines and presumes each other.  (^) In Von Neumann computational model, problem description is the sequence of instructions which specify data and sequence of control instructions and the execution of the given sequence of instructions is the interpretation of the computation.

Execution Semantics

 (^) A rule that prescribes how a single execution step is to be performed.  (^) The rule is associated with the chosen problem description method and how the execution of the computation is interpreted.