Employs an Event Confition Action rule style. An example of such rule is shown below, the rule is defined using Xpath.

<Rule name="CreateAutomaticAssignments" limit="?" evalMode="once"
level="2">
<Description>This is rule CreateAutomaticAssignments</Description>
<Initialize>
<Assert>
<Event>
<base:XPath>sim:EventDef[@eventType="BidRequest"]</base:XPath>
</Event>
<Expression>
<Property name=”Store”>
<InList name=”AutomaticAssignmentStore”/>
</Property>
</Expression>
</Assert>
</Initialize>
<Views>
<ViewRef name="CreateAutomaticAssignments">
<base:XPath>sim:ViewDef[@name=”CreateAutomaticAssignments”]
</base:XPath>
</ViewRef>
</Views>
<Situations>
<SituationRef name="CreateAutomaticAssignments">
<base:XPath>sim:SituationDef[@name="CreateAutomaticAssignments"]
</base:XPath>
</SituationRef>
</Situations>
<Actions>
<SituationDetected situationName="CreateAutomaticAssignments">
<ActionRef name="CreateAutomaticAssignments"
eventVisibility="external">
<base:XPath>sim:ActionDef[@name="CreateAutomaticAssignments"]
</base:XPath>
</ActionRef>
</SituationDetected>
</Actions>
</Rule>

Link to the page that describes how to solve FFD application using the ruleCore CEP Server.