The event defined as a SBML event. e.g.: for a event like this [G2] = ( 0 when [P1] ≤ τ, 1 when [P1] > τ) The SBML representation of the part ( 0 when [P1] ≤ τ ) is as follow: <event useValuesFromTriggerTime="true"> <trigger persistent="false" initialValue="true"> <math:math> <math:apply> <math:leq/> <math:ci> P1 </math:ci> <math:ci> tau </math:ci> </math:apply> </math:math> </trigger> <listOfEventAssignments> <eventAssignment variable="G2"> <math:math> <math:cn sbml:units="concentration"> 0 </math:cn> </math:math> </eventAssignment> </listOfEventAssignments> </event> For more information please refer to (7.11 Example involving events) in http://sbml.org/Special/specifications/sbml-level-3/version-2/core/release-1/sbml-level-3-version-2-core.pdf