In ACT-R difference between declarative and working memory
This article explains the difference :


  Declarative memory takes the form of a semantic net linking
  propositions, images, and sequences by associations.
  
  The nodes of long-term memory all have some degree of activation and
  working memory is that part of long-term memory that is most highly
  activated.




The declarative memory is all knowledge that can be retrieved in consciousness. Working memory activates only the declarative memory needed for the current task.  

When a different task is given, the activation changes to match the needs of the new task. The non-relevant active knowledge is deactivated, and new relevant knowledge is retrieved.