No Silver Bullet

1
No Silver Bullet Essence and AccidentNot
only are there no silver bullets now in view, the
very nature of software makes it unlikely that
there will be any no inventions that will do
for software productivity, reliability, and
simplicity what electronics, transistors, and
large-scale integration did for computer
hardware.
2
Productivity Equation

• Time of task SUM(frequency)i X (time)i
• Conceptual components of the task take most of
  the time (deciding what to build)
• In order to increase software productivity we
  must focus on this aspect of software development

3
Promising Attacks on the Conceptual Essence

• Buy vs. Build
• Requirements refinement - Rapid Prototyping
• Incremental development

4
Buy versus BuildThe most radical possible
solution for constructing software is not to
construct it at all

• ANY software product is cheaper to buy than to
  build
• Even at a cost of 100,000, a purchased piece of
  software is costing only about as much as one
  programmer-year
• Delivery is immediate
• The cost of software is in development, not
  replication. By sharing the cost among a large
  number of users, the per-user cost is lowered.
• Examples spreadsheets/payroll apps/accounting
  software

5
Requirements Refinement

• Most difficult step in software development
• Any mistakes in the requirements cripple the
  resulting system and are difficult to rectify
  later
• Clients generally do not know what they want or
  know what questions must be answered
• Clients almost never communicate the problem to
  the software designers in the detail that must be
  specified
• It is the designers job to iteratively extract
  and refine the product requirements from the
  client

6
Rapid Prototyping

• Prototypes generally simulate important
  interfaces and perform major functions of the
  intended system
• Prototypes are an important tool designers use to
  extract requirements specifications from the
  client
• Give clients a chance to test versions of the
  product they are specifying to designers
• Any problems in requirements are caught early in
  the design phase

7
Incremental Development

• Software is not written
• Software is grown by incremental development
• Every new function or class grows out of what is
  already in the program
• Decreases bugs
• Ease of backtracking
• Prevents the project from going off course