BPMN in Practice: Symbols, Swimlanes, Gateways, and Event Notation for Mapping Processes

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BPMN in Practice: Symbols, Swimlanes, Gateways, and Event Notation for Mapping Processes

System Analysis and Design · Chapter 3: Agile Methods and Rapid DevelopmentSection 3.9 · lesson 23 of 698 min · free with a free account

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In this lesson

Events, activities, gateways, pools, swimlanes, and the 2 kinds of arrow.

  • Identify BPMN's core symbols: events, activities, and gateways
  • Distinguish exclusive, parallel, and inclusive gateways
  • Explain pools and swimlanes, and sequence vs. message flows
  • Read a complete worked BPMN diagram from start to end

Transcript

Everything said in the video, section by section (1,072 words). Read along, or search it.

Agile Methods and Rapid Development

BPMN in Practice

The last section ended by naming B P M N as the notation most organizations standardize on. This section teaches you to read it, and to draw it. We will cover its three core symbols, three kinds of gateway, pools and swimlanes, and the two kinds of arrow. Then we will read a complete worked diagram, from start to end.

What BPMN Is

One Notation Everyone Reads the Same Way

Business process model and notation, or B P M N, is a standardized way of drawing a process. Its value is consistency. Anyone familiar with the notation, whichever company or team they work for, can read the diagram the same way. Nearly every B P M N diagram is built from just three kinds of symbol. Events are drawn as circles, and represent something that happens. A start event, drawn as a thin circle, begins a process. An end event, drawn as a bold circle, ends one. And an intermediate event marks something partway through, such as a timer, or an incoming message. Activities are drawn as rounded rectangles. They represent a unit of work, done by a person or a system, like receive order, or ship order. And gateways are drawn as diamonds. They represent a decision point, where the flow of the process can split, or merge.

Figure 1

3 Kinds of Gateway

Gateways are not all the same. And choosing the wrong one changes the meaning of the diagram. Three types cover almost every situation. An exclusive gateway takes exactly one outgoing path, based on a single condition. For example, if payment is approved, ship the order. Otherwise, notify the customer. A parallel gateway takes every outgoing path, at the same time. For example, notify the warehouse, update inventory, and email the customer, all at once. An inclusive gateway takes one or more paths, depending on which conditions apply. For example, apply a loyalty discount if the customer qualifies, and apply a promo code if one was entered. One path, every path, or some of the paths. Hold on to those three phrases. Here is why the choice matters. With an exclusive gateway, a paid order never also triggers the customer notice. Swap in a parallel gateway by mistake, and the diagram now claims both things happen every time.

Who Does What

Pools and Swimlanes

A process rarely involves just one participant. Pools and swimlanes show who is responsible for each step. A pool represents one whole participant in the process. That could be a company, a department, or an outside party, like a customer. Everything inside a pool's boundary belongs to that participant. A swimlane subdivides a pool into the specific roles or departments responsible for different activities. So it is clear, at a glance, who does what. Splitting a pool into swimlanes is optional. A simple process may use a single, undivided pool per participant, as the customer pool does in the worked example.

2 Kinds of Arrow

Sequence Flow vs. Message Flow

B P M N uses two different arrows. Mixing them up is one of the most common mistakes new readers make. A sequence flow is a solid arrow. It shows the order activities happen in, within a single pool. A message flow is a dashed arrow. It shows communication passing between two separate pools. For example, an order confirmation sent from a company to a customer. Here is the rule to remember. A sequence flow can never cross a pool boundary. Control cannot simply pass from one independent participant's process into another's. So crossing a pool boundary always requires a message flow instead. Think of it this way. A company can send a customer a message, but it cannot make the customer act. The dashed arrow captures exactly that difference.

Figure 2 - Worked Example

Placing an Order

Now let's put it all together, in a small order-processing scenario. There are two participants. A customer, at the top, in its own undivided pool. And an online store, whose work is split across two lanes. A sales lane, and a fulfillment lane. Look for the two kinds of arrow as we go. Solid arrows stay inside a pool. Dashed arrows cross between pools. And notice the circles. A thin circle starts a flow, and a bold circle ends one.

Reading Figure 2

Left to Right, Step by Step

Read the diagram from left to right. The customer's start event leads into the place order activity. Placing an order is something the customer does that the online store needs to know about. So place order connects to receive order with a dashed message flow, not a solid sequence flow. That is because the two activities belong to different pools. Inside the sales lane, a solid sequence flow carries the process from receive order to the exclusive gateway. The gateway sends it down exactly one of two paths. The yes path crosses into the fulfillment lane, to ship order. That crossing is allowed, because both lanes belong to the same pool. The no path stays in the sales lane, where the store notifies the customer. And notify customer ends with a message flow back to the customer's end event. Every arrow in the diagram obeys the rule. Solid inside a pool, dashed between pools.

A Note on the Example

Simplified on Purpose

One more thing about this example. It is deliberately simplified, to highlight the notation. A complete process would also message the customer once the order ships. In this version, the no path's message is the diagram's only communication back to the customer. That is a useful habit when you read any B P M N diagram. Ask what each participant would need to hear, and check that a message flow delivers it.

Key Terms

The Vocabulary of This Section

Let's lock in the key terms. B P M N, or business process model and notation, is a standard for diagramming processes so they read consistently. A gateway is a diamond-shaped symbol, where a process splits or merges. A pool is a boundary representing one whole participant. A swimlane subdivides a pool by role or department. A sequence flow is a solid arrow, showing the order of activities within a single pool. And a message flow is a dashed arrow, showing communication between two separate pools.

Key Takeaways

What to Carry Forward

To pull this together. Every B P M N diagram is built from three core symbols. Circular events, rectangular activities, and diamond-shaped gateways. Exclusive, parallel, and inclusive gateways look similar, but mean very different things. Exactly one path, every path, or one or more paths. Pools represent whole participants, and swimlanes divide a pool by role or department. And sequence flows, which are solid, show order within a pool. Message flows, which are dashed, show communication between pools. The two are never interchangeable.

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FAQ

Questions students ask us

About BPMN in Practice: Symbols, Swimlanes, Gateways, and Event Notation for Mapping Processes

What are the three core symbols in BPMN?
The three core BPMN symbols are events, activities, and gateways. Events are circles representing something that happens: a thin circle starts a process, a bold circle ends it, and an intermediate event marks something partway through, such as a timer or incoming message. Activities are rounded rectangles representing a unit of work, like receive order. Gateways are diamonds marking points where the flow splits or merges.
What is the difference between exclusive, parallel, and inclusive gateways in BPMN?
An exclusive gateway takes exactly one outgoing path, a parallel gateway takes every outgoing path at the same time, and an inclusive gateway takes one or more paths depending on which conditions apply. For example, an exclusive gateway ships an order if payment is approved or otherwise notifies the customer. Choosing the wrong type changes the diagram's meaning, since a parallel gateway would claim both outcomes happen every time.
What is the difference between a sequence flow and a message flow in BPMN?
A sequence flow is a solid arrow showing the order of activities within a single pool, while a message flow is a dashed arrow showing communication between two separate pools. A sequence flow cannot cross a pool boundary, because one independent participant cannot directly control another's process. So when a customer places an order with a store, the link between the two pools is drawn as a dashed message flow.
What are pools and swimlanes in a BPMN diagram?
A pool is a boundary representing one whole participant in a process, such as a company, a department, or an outside party like a customer, and a swimlane subdivides a pool into the roles or departments responsible for its activities. Swimlanes make it clear at a glance who does what. Dividing a pool into lanes is optional, so a simple participant like a customer may use a single, undivided pool.

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