DFDL expressions

DFDL expressions can be used to set some properties dynamically at processing-time.

For example, a message might contain a 'count' element whose value gives the number of occurrences of a later element that is an array. The array element uses an expression in the Occurs Count property, which refers to the 'count' element.

The DFDL expression language is a subset of XPath 2.0. Expressions follow XPath 2.0 syntax rules, but are always enclosed in braces '{' and '}'.

The properties that support DFDL expressions include:
  • assert (the test property of the assert takes the expression)
  • binary float rep
  • byte order
  • discriminator (the test property of the discriminator takes the expression)
  • encoding
  • escape character
  • escape escape character
  • initiator
  • input value calc
  • length
  • occurs count
  • output new line
  • output value calc
  • separator
  • terminator
  • text boolean false rep
  • text boolean true rep
  • text standard decimal separator
  • text standard exponent character
  • text standard grouping separator
You can use the XPath Expression Builder to build the expression. Either use content-assist on the property value, or click the property wizard button beside the property in the properties area.