Dev Corner

Data expressions can be used to describe structure of data.

Example: Data Expression with plus as concatenator

booking request = guest data + period + room type

guest data = guest name + address + paymethod
           + [passport number]

passport number = letter + {digit}*8

room state = {free | booked | occupied | repair}

account data = transfer + {account record}* + done

Example: Data Expression with implicit concatenation

guestData = guestName, address, paymethod
         [, passportNumber]

if_statement = 'if' condition 'Then' statement
              ['Else:' statement 'End If']

• + Shows the sequence of data. What comes after what.
• [ ] Shows that something is optional.
  [optional-expression]
• { }* Shows that something is repeated a number of times.
  {expression}*
  {expression}*8
  {expression}*(0:8)
  {expression}*(4:*)
• { | | } Shows a choice between several possibilities.
• B = C Shows that the composite data structure B is composed as shown by C.
• ‘free’ Shows a literal value.
• If we want a comma to separate the data parts, we
  show a comma in the formula.

Software Requirements – Styles and Techniques