Mnemonic:

• Requirements are WHAT the software must do (externally observable behavior)
• Design is HOW the solution will work (underlying mechanism)

What is a Requirement?

It is a statement describing either
1) an aspect of what the proposed system must do,
or
2) a constraint on the system’s development.
In either case it must contribute in some way towards adequately solving the customer’s problem;
the set of requirements as a whole represents a negotiated agreement among the stakeholders.

The requirements document describes all requirements for a proposed system.

Students accustomed to poor requirements received in class assignments. Payroll example of vague requirements

Better Examples: Audio Tape Calculator  Distributed Hangman  Encounter Game     Real world example - Veterans Administration

• Describing intended solution to customer.
• Serves as the basis for design by developers.
• QA will use it as standard for verifying the final product.
• Project Managers will use it to refine the project plan - cost and schedule estimates.
• Testing team uses it to develop test cases.
• Publications department uses it to write documentation.
• Advertising and promotional efforts by marketing will be based on it.
• Serves as a legal contract.

Ambiguity of Natural Language Examples:

• "Would you rather have a lion chase you or a bear?"
• "To purchase a Christmas Tree, tear off the tag and take it to the register."
• Hernandez’s lawyer, James Sultan, acknowledged for the first time during closing arguments that he was there when Lloyd was killed.

Notations

• plain english "atomic" sentences
• structured english (e.g. Employee Scheduler)
• Decision Table
• Use Cases [examples]
• User Manual
• Data Flow Diagram
• State Transition Diagrams
• Data Dictionary
• Entity Relationship Diagrams