Oracle SOA Suite 11g Skip activites by checking conditions

There might be scenarios where a user may want to skip certain activities based on certain conditions.Eg:- A user may want to skip the assign activity in case a value is already coming for a particular variable.In 10g this was done by using switch block.But in SOA Suite 11g the activities are coming with Skip condition.Almost all activites like assign,transform,invoke,receive etc has a skip condition block where a expression can be built to check for condition for which that activity should be skipped.