Complete guide to BPMN diagram types: learn about process diagrams, collaboration diagrams, choreography diagrams, and conversation diagrams. Understand when to use each diagram type and how they differ.
Table of Contents
1. Overview of BPMN Diagram Types
BPMN 2.0 defines four main types of diagrams, each serving different modeling purposes:
- Process Diagrams: Model internal processes within a single organization
- Collaboration Diagrams: Model interactions between multiple participants
- Choreography Diagrams: Model interactions from a global perspective
- Conversation Diagrams: High-level view of message exchanges
Each diagram type uses different BPMN elements and serves specific modeling needs. Understanding when to use each type is crucial for effective process modeling.
2. Process Diagrams
2.1 Definition
A process diagram models a single business process within one organization or participant. It focuses on the internal flow of activities, showing the sequence of work performed.
2.2 Characteristics
- Models a single process from start to end
- Uses sequence flows to connect activities
- May include lanes to show organizational roles
- Does not show interactions with external participants
- Most commonly used BPMN diagram type
2.3 Elements Used
- Start events and end events
- Tasks and sub-processes
- Gateways (exclusive, parallel, inclusive, event-based)
- Sequence flows
- Lanes (optional, for role-based organization)
- Data objects and artifacts
2.4 Use Cases
- Modeling internal business processes
- Documenting process workflows
- Process automation within a single organization
- Process analysis and improvement
- Employee training and documentation
2.5 Example Scenarios
- Order processing within a company
- Employee onboarding process
- Invoice approval workflow
- Product development process
3. Collaboration Diagrams
3.1 Definition
A collaboration diagram models interactions between two or more participants (pools). It shows how different organizations, departments, or systems interact through message flows.
3.2 Characteristics
- Contains multiple pools (participants)
- Uses message flows to show interactions
- Each pool may contain a process diagram
- Shows inter-participant communication
- Can include black-box pools (internal process not shown)
3.3 Elements Used
- Pools (participants)
- Lanes within pools (optional)
- Message flows (dashed lines between pools)
- Process elements within each pool
- Message events (send, receive)
3.4 Use Cases
- Modeling B2B processes
- Inter-departmental processes
- System integration scenarios
- Customer-supplier interactions
- Multi-party business processes
3.5 Black-Box Pools
A black-box pool represents a participant whose internal process is not modeled. Only the message exchanges with this participant are shown. This is useful when:
- The internal process of a participant is not relevant
- You don't have visibility into another organization's process
- You want to focus on the interaction pattern
4. Choreography Diagrams
4.1 Definition
A choreography diagram models interactions between participants from a global perspective. It focuses on the exchange of messages and the order of interactions, rather than internal processes.
4.2 Characteristics
- Shows interactions from a neutral, global view
- Uses choreography tasks (interactions between participants)
- Does not show internal process details
- Emphasizes the sequence of message exchanges
- Less commonly used than process or collaboration diagrams
4.3 Elements Used
- Choreography tasks (showing two participants)
- Choreography sub-processes
- Choreography events
- Choreography gateways
- Sequence flows between choreography elements
4.4 Use Cases
- Modeling inter-organizational processes
- Defining service contracts
- Specifying interaction protocols
- B2B integration scenarios
- When internal processes are not relevant
4.5 Choreography vs Collaboration
The key difference is perspective:
- Collaboration: Shows both internal processes and interactions
- Choreography: Shows only interactions, no internal processes
5. Conversation Diagrams
5.1 Definition
A conversation diagram provides a high-level view of message exchanges between participants. It's the simplest BPMN diagram type, showing only who talks to whom.
5.2 Characteristics
- Simplest BPMN diagram type
- Shows only participants and their conversations
- No process details or flow information
- High-level overview of interactions
- Useful for initial process discovery
5.3 Elements Used
- Participants (pools)
- Conversation nodes (representing message exchanges)
- Conversation links (connecting participants to conversations)
5.4 Use Cases
- Initial process discovery
- High-level process overview
- Identifying participants and their interactions
- Process scoping and planning
- Stakeholder communication
5.5 When to Use
Use conversation diagrams when you need to:
- Quickly identify all participants in a process
- Understand high-level interaction patterns
- Communicate process scope to stakeholders
- Plan detailed process modeling
6. Choosing the Right Diagram Type
6.1 Decision Criteria
Consider these factors when choosing a diagram type:
- Number of Participants: Single participant → Process diagram; Multiple participants → Collaboration/Choreography
- Level of Detail: High-level → Conversation; Detailed → Process/Collaboration
- Focus: Internal process → Process diagram; Interactions → Collaboration/Choreography
- Audience: Technical → Process/Collaboration; Business → Conversation/Choreography
6.2 Comparison Table
| Diagram Type | Participants | Shows Internal Process | Complexity |
|---|---|---|---|
| Process | Single | Yes | Medium to High |
| Collaboration | Multiple | Yes (for each pool) | High |
| Choreography | Multiple | No | Medium |
| Conversation | Multiple | No | Low |
7. Relationships Between Diagram Types
7.1 Hierarchical Relationship
Diagram types can be used together in a hierarchical manner:
- Conversation → Collaboration: Start with conversation to identify participants, then detail with collaboration
- Collaboration → Process: Each pool in a collaboration can contain a detailed process diagram
- Choreography → Collaboration: Choreography can be refined into collaboration diagrams
7.2 Modeling Approach
A typical modeling approach:
- Start with a conversation diagram to identify participants
- Create a collaboration diagram to show interactions
- Detail each pool with a process diagram
- Optionally create choreography diagrams for contract definition
7.3 Consistency
When using multiple diagram types for the same process:
- Ensure participant names are consistent
- Message flows in collaboration should match choreography tasks
- Conversation nodes should align with message exchanges
- Maintain consistency in level of detail
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