A Blended Workflow Approach António Rito Silva INESC-ID/IST/Technical University of Lisbon Rito.Silva@ist.utl.pt Abstract. Semi-structured workflow approaches are being recognised as essential to support collaboration whenever ad-hoc work needs to be performed due to the occurrence of unanticipated events in dynamic environments. However, semi-structured workflows need to balance the support of unexpected situations with guidance for the situations where a standard behaviour is wanted. The blended workflow approach proposes an integration of two distinct workflow specifications, the activity-based specification, which precisely defines how to coordinate work for expected situations, and a goal-based specification, which empowers people to ac- complish the business process goals using their tacit knowledge. In this paper we describe the blended workflow approach, illustrate it with an example, and identify the compliance properties that a blended workflow approach needs to have to integrate activity and goal specifications. Key words: Activity-based workflow, Goal-based workflow, Semi-structured workflows, Flexible workflows 1 Introduction Today’s mainstream workflow systems are activity-based. They focus on how activities can be coordinated using control flow primitives, as sequential and parallel execution, to achieve the business process goals [1, 2]. Activity-based workflows prescribe the activities execution order but lack flexibility to handle unexpected situations for which they were not codified. A new set of workflow approaches is emerging which fosters end users collab- oration to deal with unexpected situations, e.g., ActionBase [3]. These workflows support ad-hoc behaviour and delegate to end users the responsibility to guaran- tee that the business process goals are achieved. However, they lack the guidance provided by activity-based workflows. In this paper we propose a new approach, called blended workflow, which intends to bridge the gap between completely structured workflows and ad-hoc workflows. The idea behind the blended workflow approach is that a workflow management system should allow end users to deviate from the structured ex- ecution whenever it is necessary, yet may allow them to regain the guidance provided by structured workflows once the unexpected situation is dealt with. To do so, blended workflow proposes the coexistence of two workflow specifi- cations, a prescriptive activity-based specification and a descriptive goal-based