Consider the nature of a computer as a tool

1
To begin with...

• Consider the nature of a computer as a tool
• Non conventional in that its universal
• Reasons for it being so (separation of entities)
• The current computer organisation model (Von
  Neumann)

COMPUTING SYSTEM
physical processing part
abstract control part
2
The current computer organisation model (Von
Neumann)

• The model parts
• Inference The abstract control structure should
• basically conform to this model

The data storage part
The processing part
The input/output part
3
Algorithm components

• Tightly based on the hardware organisation
  they are to control
• Processing (executive) components
• Data storage (memory) components
• Inputting (data receiving) components
• Outputting (data transmitting) components

4
Data

• In singular form, datum.
• Datum \Da"tum\, n. pl. Data. L. See 2d Date.
  1. Something given or admitted a fact or
  principle granted that upon which an inference
  or an argument is based -- used chiefly in the
  plural.
• Websters Revised Unabridged Dictionary (1913)
• Data in its pure form is actually meaningless
• For data to convey meaning it must be given
  structure
• Information Data Structure

5
Abstract data controlling the hardware (i. e.
software)

• No modern idea - has been around since Victorian
  era (Charles Babbage Ada Lovelace)
• Renders a computing system different from other
  tools (universality)
• Forces a more formal definition of process models
• Must match human thought patterns
• Must be represent-able
• Must be understandable to both human and machine

6
The idea of an algorithm

• A possible informal definition
• A stepwise description of time separated actions
  with respect to time which are required to
  perform a definite task
• Steps preceding the effective application of an
  algorithm
• Conceive the task
• Define the task
• Specify the requirements
• Entities resulting from the effective application
  of an algorithm
• The implemented system or a model of it
• The systems complete and matching documentation
• The softwares full and matching description

7
Desirable algorithm properties

• Clear
• Unambiguous
• Alterable
• Correct (with respect to basic formally provable
  principles)
• Easy to comprehend functionality (relatively)

8
The status quo in computing

• Historically hardware has always developed at a
  faster rate than software
• This fact was not given real importance till the
  late 1980s
• Hardware must be engineered to work at all while
  software need not
• Software is expected to contain bugs
• Software is fragile
• Your life could very well depend on software
• Conclusion Software is at least as important as
  hardware (if not more in some aspects)

9
ThereforeSOFTWARE MUST BE ADEQUATELY
ENGINEERED RATHER THAN SIMPLY THOUGHT UP AND
WRITTEN(hence the term Software Engineering)
10
Some disturbing facts about software
development in the late 1980s and early 1990s
(1/2)

• Most software was never well planned from the
  start and was never designed using rigorous
  design methods
• Software was not quantifiable or qualify-able
  until its actual application
• Software was extremely fragile (i.e. unreliable)
• Software rarely fully matched its requirements

11
Some disturbing facts about software
development in the late 1980s and early 1990s
(2/2)

• Software development involved considerable
  duplication of effort
• The idea of software prototyping was to run the
  system and do a post-mortem check when it failed
• When software did work well and reliably there
  was a rush to find out why!
• Conclusion Founding a discipline based on such
  ad hoc software development methods is not
  feasible!

12
High demand on software

• The demands and expectations from software is
  nowadays dramatically increasing by literally by
  the day. People are starting to appreciate the
  idea of fully reliable software. Particular
  critical areas include
• Real-time embedded systems
• Safety-critical systems
• High finance
• Machine automation
• Life-critical systems
• Civil
• Military
• Any others I might have left out.

13
Strange sort of situation

• Machine hardware is generally well engineered
  (otherwise it probably wouldnt work at all)
• Software is recognised to be crucial
• Software controls the functioning of machine
  hardware in an absolute sense
• Software is often not engineered well (or at all)
• Faulty software inevitably means machine
  (computer) malfunction
• People are happy to entrust their dearest
  possessions, and indeed, their life to computers
  or computer controlled systems.

14
The panic!

• In the mid 80s people began to worry about the
  sorry state of software development.
• By the late 80s this worry became a panic, the
  main reasons being
• The evident poor quality of software
• The huge jump in reliability demand as software
  started to control even more critical aspects of
  society
• The very poor choice (if any) of software design,
  verification and implementation standards
• People simply didnt pay serious enough attention
  to software in the past - now that a crises was
  created, attention was force-focused on it.