Data Structure-Oriented Design (Early 70s)

Q: Explain about 'Data Structure-Oriented Design (Early 70s)'

• Soon it was discovered:

-        it is important to pay more attention to the design of data structures of a program

*        than to the design of its control structure.

• Techniques which emphasize designing the data structure:

-        derive program structure from it:

*        are called data structure-oriented design techniques. 

• Example of data structure-oriented design technique:

-        Jackson's Structured Programming(JSP) methodology

*        developed by Michael Jackson in 1970s.

• JSP technique:

-         program code structure should correspond to the data structure.

• In JSP methodology: 

-        a program's data structures are first designed using notations for 

*        sequence, selection, and iteration. 

-        Then data structure design is used :

*        to derive the program structure.

• Several other data structure-oriented Methodologies also exist:

-         e.g., Warnier-Orr Methodology. 

Data Flow-Oriented Design  (Late 70s)

• Data flow-oriented techniques advocate:

-        the data items input to a system must first be identified,

-        processing  required on the data items to produce the required outputs should be determined.

• Data flow technique identifies:

-        different processing stations (functions) in a system 

-        the items (data) that flow between processing stations.

• Data flow technique is a generic technique:

-        can be used to model the working of any system

·        not just software systems.

•  A major advantage of the data flow technique is its simplicity

Data Flow Model of a Car Assembly Unit

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difference betwen control flow oriented and data flow oriented design

Q: State at least two basic differences between control flow-oriented and data flow-oriented design techniques.
Ans.: - Control flow-oriented design deals with carefully designing the program’s control structure. A program's control structure refers to the sequence, in which the program's instructions are executed, i.e. the control flow of the program. But data flow-oriented design technique identifies:
• Different processing stations (functions) in a system
• The data items that flows between processing stations

Identify at least two advantages of using high-level languages over assembly languages.

Q: Identify at least two advantages of using high-level languages over assembly languages.
Ans.: - Assembly language programs are limited to about a few hundreds of lines of assembly code, i.e. are very small in size. Every programmer develops programs in his own individual style - based on intuition. This type of programming is called Exploratory Programming.
But use of high-level programming language reduces development efforts and development time significantly. Languages like FORTRAN, ALGOL, and COBOL are the examples of high-level programming languages.

Emergence of Software Engineering?

5. Emergence of Software Engineering?

Ans:
  Early Computer Programming (1950s):

-        Programs were being written in assembly language.

-        Programs were limited to  about a few hundreds of lines of assembly code.

• Every programmer developed his own style of writing programs:

-        according to his intuition  (exploratory programming).

High-Level Language Programming (Early 60s)

• High-level languages such as FORTRAN, ALGOL, and COBOL were introduced:

-        This reduced software development efforts greatly.

• Software development style was still exploratory.

-        Typical program sizes were limited to a few thousands of lines of source code.

Control Flow-Based Design (late 60s)

• Size and complexity of programs increased further:

-        exploratory programming style proved to be insufficient. 

• Programmers found: 

                  -        very difficult to write cost-effective and correct programs

-        programs written by others very difficult to understand and maintain.

• To over come with this problem, experienced programmers advised: ``Pay particular attention to the   design of the program's control structure.'’               
• A program's control structure indicates:

-         the sequence in which the program's instructions are executed.

• To help design programs having good control structure:

-        flow charting technique was developed.

• Using  flow charting technique:

-        one can represent and design a program's control structure.

-        Usually one understands a program:

·        by mentally simulating the program's execution sequence

• A program having a difficult(messy) flow chart representation:

-        difficult to understand and debug.

• It was found:

-        GO TO statements  makes control structure of a program messy(difficult, unorganized)

-        GO TO statements alter the flow of control arbitrarily.

-        The need to restrict use of GO TO statements was recognized.

• Many programmers  had extensively used assembly languages.

-        JUMP instructions are frequently used for program branching in assembly languages,

-        programmers considered use of GO TO statements inevitable.

• But, soon it was conclusively proved:

-        only three programming constructs are sufficient to express any programming logic:

·        sequence  (e.g. a=0;b=5;)

·        selection (e.g.if(c=true) k=5 else m=5;)

·        iteration   (e.g. while(k>0) k=j-k;)

• Everyone accepted:

-        it is possible to solve any programming problem without using GO TO statements.

-        This formed the basis of  Structured Programming  methodology.

What is Computer Systems Engineering?

5. What is Computer Systems Engineering?

Ans:

• Computer systems engineering:

-        encompasses software engineering.

• Many products require development of software as well as specific hardware to run it:

-         a coffee vending machine,

-        a mobile communication product, etc.

• The high-level problem:

-        deciding which tasks are to be solved by software

-        which ones by hardware.

• Often, hardware and software are developed together:

-        Hardware simulator is used during software development.

• Integration of  hardware and software.
• Final system testing

Programs versus Software Products?

4. Programs versus Software Products?

PROGRAMS	S/W PRODUCT
Usually small in size Author himself is sole user Single developer Lacks proper user interface Lacks proper documentation Ad hoc(Not Systematic or unplanned) development.	Large Large number of users Team of developers Well-designed interface Well documented & user-manual prepared Systematic development

What is Software Crisis

3. What is Software Crisis

Software Crisis

·Software products:

-fail to meet user requirements.

-frequently crash.

-expensive.

-difficult to alter, debug, and enhance.

-often delivered late.

-use resources non-optimally.

Factors contributing to the software crisis

·Larger problems,

·Lack of adequate training in software engineering,

·Increasing skill shortage,

·Low productivity improvements.