 Camunda

BPMN Modeling Reference

All BPMN 2.0 Symbols Explained

Overview

Participants
Pool

Lane

Activities
Task

Subprocess

Call Activity

Adhoc

Event Subprocess

Gateways
Exclusive (XOR)

Parallel (AND)

Inclusive (OR)

Event-based

Events
Basic Concepts

Message

Timer

Error

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 Conditional

Signal

Termination

Link

Compensation

Multiple

Parallel

Escalation

Cancel

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Overview
Symbol Overview
Coverage in process engine: If you are interested which elements can be automated using the camunda BPMN 2.0
process engine check out our BPMN 2.0 Coverage.

Participants
Lane
Pool

Artifacts
Group
Text
Annotation

Gateways
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Exclusive Inclusive Parallel Event

Data
Data
Object Data
Store

Activities
Task Subprocess Call Activity Event Transaction
Subprocess

Events
Heads up!
For understanding the principle behavior of events in BPMN, check out Events: Basic Concepts.

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 Type Start Intermediate End

Normal Event Subprocess Event Subprocess catch boundary boundary throw

non-interrupt non-interrupt

None

Message

Timer

Conditional

Link

Signal

Error

Escalation

Termination

Compensation

Cancel

Multiple

Multiple Parallel

Participants
Introducing Pools, the conductor and the orchestra
We already described how to use lanes to assign responsibility for tasks or subprocesses to different task managers.
Lanes always exist in a pool, and the lane boundaries represent process boundaries from start to end. To BPMN, the
pool represents a higher-ranking instance compared to its lanes. The pool assumes process control - in other words, it
assigns the tasks. It behaves like the conductor of an orchestra, and so this type of process is called "orchestration."

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In the diagram below, the "conductor" arranges for Falko to process task 2 as soon as Robert completes task 1. The
conductor has the highest-level control of the process, and each instrument in the orchestra plays the tune the
conductor decides upon:Robert

task 1

start
Falko

task 2
process conductor

Christian

task 3
Stefan

task 4

Do you think this is unrealistic? Many experienced process modelers have problems with this way of thinking. They would
prefer to model a process sequence like that shown below on the assumption that no almighty conductor exists in their
company, and that individual process participants have to coordinate and cooperate on their own:

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 Robert

task 1 passing on to
Falko

start
Falko

passing on to
task 2
Christian
Christian

passing on to
task 3 Stefan
Stefan

task 4

But to coordinate cooperation with BPMN requires explicit modeling. You assign each task manager a separate pool, and
the process passes from one to the next as a message flow as shown in below. In principle, this creates four independent
conductors. These have control over their respective mini-processes, but they can't do anything other than to send
messages that trigger their successor processes:

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 Robert

task 1 passing on to
Falko

start
Falko

passing on to
task 2
Christian

start
Christian

task 3 passing on to
Stefan

start
Stefan

task 4

start

That seems complicated - and you don't have to choose this method for practical modeling. It reveals a basic principle,
however, that you must understand. Even though BPMN lanes look very much like those of other process notations, they
represent an entirely different way of thinking, which we attribute to BPMN's origin in the world of process automation.
In that world, the process engine controls all tasks in the process, even though different task managers may execute
them. So the process engine equates to the mysterious, almighty process conductor.
Have you heard of service orchestration in connection with Service Oriented Architecture (SOA)? That's almost exactly
the task of a process engine, except that these services are not only fully automated web services; they also can be tasks
executed by human process participants as directed by the process engine. What does that signify, however, for purely
functional process modeling, in which you also describe processes not controlled by such a process engine? There's no
general answer to that question.
You can eliminate pools and work just with lanes, modeling the message exchange as normal tasks as shown before.
That's traditional, and it's a pragmatic solution during, say, a transitional period that allows your co-workers to adapt. In
the medium and long terms, however, avoiding pools denies you a powerful device for increasing the significance of
process models.
We will show the usefulness of this new thinking by example. One thing to remember is that if you strive to harmonize
your functional and technical process models to achieve a better alignment of business and IT, you inevitably face this
type of process modeling whether you use BPMN or not.

Pools: The art of collaboration

We already examined the process represented below in connection with the event-based gateway:
Now consider the broader picture, and think about how this process happens from the point of view of the pizza delivery
service. Presumably, it looks like here: As soon as we receive an order, we bake the pizza. Our delivery person takes it to
the customer and collects the money, whereby the process completes successfully.

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 pizza baker
bake pizza
pizza sales
supplier

Bestellung
erhalten
delivery boy

deliver pizza take the money

end

we want to link the two processes, that is, to examine the interaction of customer and delivery service from a neutral
perspective. We can try to model this interaction by means of a pool and lanes as in here:

choose pizza order pizza

customer

hunger pizza
noticed receiveid

call pizza
delivery service
pizza- process

60 minutes pizza received

pizza baker

bake pizza
supplier

delivery boy

deliver pizza take the

money

But this doesn't work well: There are tasks and events that reference interaction within the pool - waiting for the delivery,
for instance, or collecting the money. Other tasks are carried out by roles oblivious to their partners, such as baking the
pizza and eating the pizza. It is impossible to differentiate the two visually. Strictly speaking, the diagram is not
semantically correct because message events always refer to messages received by the process from outside, and that's
not the case here.
If we go with pools, the whole process looks like below. Both processes in the combined representation would look just
as they did before, but now they connect through message flows. BPMN calls this form of visualization a collaboration
diagram. It shows two independent processes collaborating.

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 choose pizza order pizza eat pizza
pizza order
customer

hunger pizza received

noticed
call pizza
delivery service

60 minutes pizza received

Pizza-Bäcker

bake pizza
pizza sale

order received
supplier
Lieferjunge

take
deliver pizza the money

end

In two cases, the message flows do not end in an activity or event, but at the participants' respective pool boundaries.
The first one comes from the "inquire at delivery service" task; the second one connects to the "collect money" task. The
rationale behind the first one is that our inquiry does not influence the sequence flow of the deliverer. The pizza service
may provide information or speed up its order processing in anticipation of a new order, but the baking, delivering, and
collecting of money doesn't change just because an inquiry came in. As for the "collect money" messages, there's a flaw
in the model of the customer process: we have to pay for the pizza before we eat it, and that task is still missing. We
added it to the diagram below, and now we can connect the message flows directly to the "pay for pizza" task.

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 choose pizza order pizza pay for pizza
pizza order
customer

hunger pizza received

noticed

call pizza
delivery service

60 minutes
pizza baker

bake pizza
pizza sales
supplier

order
received
delivery boy

take
deliver pizza the money

end

Collapsing Pools
It often happens that we don't know the processes of all parties in detail. We may know the processes of our own
company, for example, but not those of a partner company. As long as our partner and we adhere to agreed-upon
interfaces, such as receiving or sending certain messages, things can still operate smoothly. As customers of the pizza
delivery service, we expect the deliverer to:
Accept pizza orders,
Deliver ordered pizzas and collect the money, and
Be available for inquiries.
As customers, we have little interest in the deliverer's internal process. Maybe he bakes and then delivers the pizza;
maybe when he's out of supplies, he gets another pizza service to bake the pizza and deliver it. That's his problem - we
simply expect to receive our pizza. In modeling such cases, we can hide the deliverer's process and collapse the pool:

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 choose pizza order pizza pay for pizza
pizza order
customer

hunger pizza
noticed received

call pizza
delivery service

60 minutes pizza
received

supplier

We could go a step further and collapse the customer's pool too. Now we see only the messages to be exchanged,
assuming that we label the arrows to give us the general idea. The downside is that we can't recognize
interdependencies any more. We can't see if the inquiry always goes out, or only takes place under certain conditions -
the actual case:

pizza order - customer

order inquiry delivery take the money pay

pizza delivery - supplier

Lanes
We have talked about what to do in our processes, but we have not yet explained who is responsible for executing
which tasks. In BPMN, you can answer this question with lanes.
Hover over orange symbols for explanation

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 Christian

choose recipe cook pasta eat meal

something pasta
real
hunger desired desired dish?
noticed component?
flat-sharing community

steak
Falko

cook steak
salad
Robert

prepare salad

The diagram shows that the tasks in our sample process were assigned to particular people. We can derive the following
process description from the assignments: If Christian is hungry, he chooses a certain recipe. Depending on what
Christian chooses, he can either take care of it himself (cook pasta), or he can get his roommates on board. If the latter,
Falko cooks steak and Robert prepares salad. In the end, Christian eats. The three lanes (Christian, Falko, Robert) are
united in one pool designated "flat-sharing community."

 FAQ: Do I have to label a lane with a concrete person?

In the example, lanes equate to people, but this meaning is not specified by BPMN. You can designate the lanes as
you like. In practice, lanes are often used to assign:
Positions in the primary organization, for example, accounting clerk.
Roles in the secondary organization, for example, data protection officer.
General roles, for example, customer.
Departments, for example, sales.
IT applications, for example, CRM system.

Activities
Task
So far, we have used only tasks of undefined types, though BPMN provides the opportunity to work with task types just
as it does for event types. Primarily, task types are intended to model processes that are technically executable. Task
types are applied infrequently in practice. We know from experience, however, that task types can be particularly useful

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when modeling engineering requirements.
Hover over orange symbols for explanation

undefined receive script

receive
manual service
(instantiated)

user send business rule

Task Markers
In addition to those various types of tasks, we can mark tasks as loops, multiple instances, or compensations. Markers
can be combined with the assigned types.

Loop
A loop task repeats until a defined condition either applies or ceases to apply. Perhaps we suggest various dishes to our
dinner guests until everyone agrees. Then, we can prepare the meal:

until everyone
agrees

suggest dish prepare meal

time for meal

dinner prepared

In the example, we executed the task first and checked afterwards to see if we needed it to execute again. Programmers
know the principle as the "do-while" construct. We can also apply a "while-do" construct, however, and so check for a
condition before the task instead of afterward. This occurs rarely, but it makes sense if the task may not execute at all.
You can attach the condition on which a loop task executes for the first time or, as shown in the example, apply the
condition on repeated executions as an annotation to the task. You can store this condition as an attribute in a formal
language of your BPMN tool as well. That makes sense if the process is to be executed by a process engine.

Multiple Instance
The individual cycles of a loop task must follow each other. If for example we live in a flat-sharing community and the
roommates feel like eating pizza, the "choose pizza" task must be repeated for each roommate before we can order.
You'd sit together and pass a menu around until finally everyone has made a decision. There are student apartments
where they do handle it like that - more evidence that students have too much time on their hands! It is much more
efficient for all roommates to look at the menu at once, and they choose a pizza together. You can model this process
using the "multiple task" (see below). A multiple task instantiates repeatedly and can be executed in sequence or in

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parallel, with the latter being the more interesting case.

everyone in the
flat

choose pizza order pizza

shared flat pizza

craves pizza ordered

Do you think the example is absurd? How does your company check invoices for group orders, such as for office
supplies? Do you forward the invoice from one employee to the next, so that each person can sign off on the items he or
she ordered, before you pay the invoice? If so, you live in a flat-sharing community, and you urgently should consider
optimizing your process. Automating invoices is still one of the top BPM projects, and the top goal of such projects often
is one of parallelization.

Compensation
We explain the benefit of the compensation event in TODO by means of an example. The compensation task type is
applied exclusively in the context of a compensation event. Accordingly, it is integrated in the process diagram only by
associations, never by sequence flows.
The possible combination of the compensation with a loop or multiple instance as shown below is worth mentioning. In
this case, both markers are placed in parallel. As with the other markers, the compensation can be combined with the
task types already introduced. A manual compensation task that repeats until it succeeds or that executes repeatedly
and in parallel as far as possible, is therefore eminently practical.

... book trip ...

manual loop
compensation
cancel trip

call the travel agency

again and again until it
carves in

invite all
... friends via ...
mass email

manual parallel
compensation
uninvite
everyone via
phonecall

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Subprocess
Encapsulate complexity
The examples in this tutorial either deal with simple processes, or they diagram complex processes superficially so that
the models fit on one page. When modeling your process landscape, you don't have this luxury. You have to rough out
your processes so that you can get the general ideas in place and recognize correlations. Then you have to develop a
detailed description, so that you can analyze exactly where the weak points are or how you'll have to execute the process
in practice. The possible top-down refinements or bottom-up aggregations mark the difference between true process
models and banal flow charts, between sophisticated BPM software products and mere drawing programs.
BPMN provides us with the subprocess to help with the expanding/collapsing view. A subprocess describes a detailed
sequence, but it takes no more space in the diagram of the parent process than does a task. Both tasks and
subprocesses are part of the activities class and are therefore represented as rectangles with rounded corners. The only
difference is the plus sign, indicating a stored detailed sequence for the subprocess:
main process

activity subprocess

start end

What good is that to us? That depends most on how your BPMN tool supports the following options for connecting
subprocesses with their parent processes:
Representation in a separate process diagram: The subprocess symbol links to a separate diagram. If your BPMN
tool displays the process model in a web browser, for instance, clicking on the symbol would open a new page to
display the detail diagram.
Expanding in the process diagram of the parent process: The activity with the plus sign is called a collapsed
subprocess. The plus sign suggests that you could click on it and make the subprocess expand. The BPMN
specification provides for this option, though not all tool suppliers implement it. The diagram below shows how the
subprocess was directly expanded in the diagram of the parent process. A tool supporting this function enables
you to expand and collapse the subprocess directly in the diagram, respectively, to show or hide details.

subprocess
main process

task task task

start end

Direct expansion may seem appealing, but often it is not useful in practice. Expanding the subprocess requires that all
the adjacent symbols in the diagram shift to make room. This can result in sluggish performance with a complex
diagram, and it can be visually nasty. The most important thing is that your tool provides for linking and that you can
usefully navigate through the diagrams. In other words, it supports the first option above. Yes, it can be helpful to have
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your subprocess modeled and expandable directly from the parent process. That means process segments remain
localized, and you can attach events too. This is, however, the less important option.
The sequence flow of the parent process ends in both cases at the left edge of the subprocess. The next sequence flow
starts at the right edge. This means that sequence flows are not allowed to exceed the boundaries of the subprocess,
which not every beginner knows, and which becomes a problem when a subprocess expands. Visualize a token that
behaves as follows:
The parent process starts, and a token is born.
The token runs through the task and arrives at the subprocess, which causes the parent process to create an
instance of the subprocess.
Within the subprocess, a separate token is born which runs through the subprocess from the start to the end
event, but the token of the parent process waits until the subprocess completes.
When the subprocess token arrives at the end event, it is consumed, which completes the subprocess. Now the
token of the parent process moves to its own end event.
The encapsulation in subprocesses that we're describing isn't restricted to two levels. You could just as easily have a
parent process as a subprocess, or you could model further subprocesses on the level of a defined subprocess. How
many levels you use and the level of detail you apply to model them is up to you. BPMN doesn't specify this, and there
can be no cross-company or cross-scenario cookbook to define levels. Participants in our BPMN workshops don't like
this, but there's no point in hiding the fact nor attempting to explain it away. In the following chapters, we work often
with subprocesses in explaining our best practices, but the truth is the number of refinement levels and their respective
levels of detail is always situational. It depends on the organization, the roles of the project participants, and the goals for
the process you're modeling.

Attaching Events
We already learned about intermediate events that can be attached to tasks. The same events can be attached to
subprocesses as well, which opens up a wide range of opportunity in process modeling. As shown in the diagram below,
we can represent how a spontaneous dinner invitation leads to canceling our cooking process. In the process shown,
however, we could ignore the invitation if our meal had already been prepared and we are already eating it:

choose recipe prepare meal eat meal

hunger hunger
noticed satisfied

go out for dinner

Where message, timer, and conditional events are involved, the parent process always aborts the subprocess when
reacting to external circumstances. With error, cancellation, and escalation events, however, the subprocess reports
these events to the parent process. This isn't as abstract as it may sound.

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 check financial
availability ship article management
yes
order processing

order article
received available?
no
procurement

not inform delete article

available customer from catalogue

end

procurement place order expect delivery

stock maintenance

yes

minimum stock article procurement start available?

levle reached procured
no
not delete article
available
from catalogue

article not
deleted available

In the bottom right of the diagram above, the item procurement task can fail because the item is no longer available.
Because item procurement is a global subprocess, it triggers an error event to tell the parent process that something
went wrong. In business terms, this may mean that the customer who wanted to buy the item tells a salesperson that his
or her order failed because the item is out of stock.
It is interesting that parent processes can handle the error message differently. While the disappointed customer must
be informed within the scope of the order process, it is sufficient for the stock maintenance process to delete the item
from the catalog. The respective parent processes decide what circumstances require canceling the subprocess and
what happens next. That's a principle that you can use to build flexible and modular process landscapes.
The signal event serves two functions. A parent process can react to a signal received from the outside while it executes
a subprocess - this is much like a message event. But we also use the signal event to let the subprocess communicate
things other than errors to the parent process. Primarily, this is because we can't model this type of communication with
message events. BPMN assumes that we always send messages to other participants who are outside of our pool
boundaries; the communication between parent and subprocess doesn't fit that mold. We don't use signal events for
directed communication, but rather to broadcast information akin to advertisements on the radio.
A better alternative provided in BPMN 2.0 is the escalation event. The subprocess can use an escalation event to report
directly to the parent process, and the message won't be regarded as an error message. Also, the parent process can
receive and process messages from escalation events without canceling the subprocess because non-interrupting
intermediate events can be attached:

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 check financial
availability ship article
management
yes

order article
received available?
no procurement
order processing

inform
not available late delivery customer

end

inform delete article

customer from catalogue

end

place order expect delivery

in< 2
days
start
procurement

available?
in> 2
days

no
late
delivery

not
available

Call Activity
Modularization and reuse
In version 1.2, BPMN differentiated between embedded and reusable subprocesses by assigning an attribute to a
subprocess. In version 2.0, BPMN maintains this differentiation in principle, but it is defined differently. A subprocess now
is embedded intrinsically, and it can be reused only by defining it as a global subprocess, and then referencing it by
means of a call activity. We therefore refer to embedded subprocesses and global subprocesses in the following.
An embedded subprocess can occur only within a parent process to which it belongs. An embedded subprocess cannot
contain pools and lanes, but it can be placed within the pool or the lane of the parent process. Furthermore, an
embedded subprocess may have only a none start event; start events such as messages or timers are not permitted. An
embedded subprocess has essentially nothing more than a kind of delimited scope within the parent process, which may
serve two goals:
To encapsulate complexity (as already described)

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 To formulate a "collective statement" on a part of the parent process by attaching events or placing markers. We
deal with this option later.
On the other hand, global subprocesses may occur in completely different parent processes. There are a great many
subprocesses that, in practice, are used over and over. A good example is the procurement of an item because a
customer ordered it or you need to re-stock supply. Another example is invoicing because you've delivered or repaired
an item as shown in the diagram below. In the example, notice that call activities differ from regular activities by their
considerably thicker borders:

financial
check settlement
ship article
order processing

availability
yes

order article end

received available?
no article
procurement
stock maintenance

article financial
repair

procurement management
carry out repair

minimum stock article repair order end

levle reached procured received

...
financial settlement
article procurement

place order ... send invoice payment

received

start start
...

term of payment
exceeded

The connection a global subprocesses has to its parent is considerably less close, and they can have their own pools and
lanes. You can think of the participant responsible for a subprocess as a service provider for various parent processes. It
is a like a shared service center.
The loose connection also affects data transfer between the parent and the subprocess. BPMN assumes that embedded
subprocesses can read all the data of the parent process directly, but an explicit assignment is required for global
subprocesses to be able to read it. That may seem like merely a technical aspect at first, one that modelers and the
consumers of their models care to know about but won't wish to bother with. After some consideration, however, you
may see the impact this difference makes on the organization. Consider this: When your accounting department wants
to issue an invoice for a repair, it always needs:
A billing address

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 The date of performance delivery
A description of performance
An amount to invoice
An expected date of payment
The owners of order processing, not just the repair department, must provide this data. Accounting will want the data in
a standard format, won't it? This corresponds well to what BPMN calls required data mapping between parent processes
and global subprocesses. (Do you notice how often these weird techie issues correspond to the organizational needs
and expectations of a process?) BPMN simply forces us to formalize many matters that seem self-evident, or that
remained unconscious or forgotten in the process design. Formalization is our best chance of keeping up in a fast-
changing environment with ever more complex processes.

Adhoc
One marker available only for subprocesses is called ad-hoc. Recognize it by the tilde character as shown in the diagram
below:

switch off create auto

heating response

...

2 days before give key to

departure neighbour pack bags

Use the ad-hoc subprocess to mark a segment in which the contained activities (tasks or subprocesses) can be:
Executed in any order,
Executed several times, or
Skipped.
Any party who executes this subprocess decides what to do and when to do it. You could say that the "barely structured"
nature of what happens inside this subprocess reduces the whole idea of process modeling to an absurdity because
what happens and when are the things we most want to control. On the other hand, this is the reality of many processes,
and you can't model them without representing their free-form character. Frequent examples are when a process relies
largely on implicit knowledge or creativity, or when different employees carry out a process differently. You can use the
ad-hoc subprocess to flag what may be an undesirable actual state. Doing so could be a step on the path to a more
standardized procedure.
BPMN 2.0 specifies which symbols must, which may, and which are forbidden to occur within an ad-hoc subprocess. They
are:
Must: Activities
May: Data objects, sequence flows, associations, groups, message flows, gateways, and intermediate events
Forbidden: Start and end events, symbols for conversations and choreographies
By means of the specification, mixed forms - so-called weakly structured processes - can be modeled as shown in here:

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Event Subprocess
BPMN 2.0 introduced a completely new construct, the event subprocess. We locate an event subprocess within another
process or subprocess. Recognize them by their dotted-line frames.
A single start event always triggers an event subprocess, and this can only happen while the enclosing process or
subprocess remains active. For event subprocesses, there can be interrupting (continuous line) and non-interrupting
(dashed line) events. This is the same differentiation made as for attached intermediate events. Depending on the type of
start event, the event subprocess will cancel the enclosing subprocess, or it will execute simultaneously. You can trigger
non-interrupting event subprocesses as often as you wish, as long as the enclosing subprocess remains active.
Okay, that's pretty abstract, but we can demonstrate how an event subprocess works with an example:

meal preparations

choose recipe prepare meal

include guest

take new guest

into account
invite friends for
dinner eat meal
a new guest
has announced
himself

provide meal

order meal

cooking meal
failed

We invited a couple of friends for dinner. This starts the "dinner preparation" subprocess of choosing a recipe and then
preparing the meal. While we are doing that, the telephone rings. Another guest invites himself to dinner. Spontaneous
as we are, we just increase the amount of food or set another place at the table without interrupting the meal
preparation. If an accident happens during preparation, however, the error immediately triggers the interrupting event
subprocess for remedial action. We order food for delivery. When this event subprocess completes, we exit the enclosing
subprocess through the regular exit and attend to eating the meal.
You can see below how event subprocesses are represented in collapsed state: The frame is a dotted line, and we have
again used the plus sign to represent collapsed subprocesses. In the top left corner, we also have the start event
triggering the subprocess (TODO).

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 meal preparations

choose recipe prepare meal

invite friends for eat meal

dinner

include guest provide meal

The event types that can trigger both interrupting and non-interrupting event subprocesses are:
Message
Timer
Escalation
Conditional
Signal
Multiple
Multiple parallel
There are two more types for the interrupting event subprocesses:
Error
Compensation

Gateways
Data-based Exclusive Gateways
Hover over orange symbols for explanation

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 choose recipe cook pasta eat meal
pasta

hunger desired
noticed dish?
steak

cook steak
salad

prepare salad

Certain things can only be done under certain circumstances, so few processes always take the same course. In our
simple example, we want to go into the details of cookery. Driven by hunger, we think about what we are going to cook
today. We only know three recipes, so we choose one. We can either cook pasta or cook a steak or prepare a salad. Let's
say that these options are exclusive - we will never prepare more than one at a time. The point of decision on what to do
next is called gateway. We decide based on available data (the chosen recipe) and we follow only one of the paths, which
is a data-based exclusive gateway. We abbreviate "exclusive gateway" as XOR.
Heads up! Bear in mind that a gateway is not a task! You have to determine facts and needs before reaching a gateway.

 Best Practice: Naming Conventions

As in the diagram above, we place the crucial question before the gateway. This is our convention, which has proved
its value in our projects. Possible answers go on parallel paths after the gateway, which is how the BPMN
specification shows them. We always work with XOR gateways as follows:
Model the task that requires a decision for the XOR gateway.
Model the XOR gateway after that. Create a question with mutually exclusive answers.
Model one outgoing path (or sequence flow) for each possible answer, and label the path with the answer.

 FAQ: Do I have to draw the "X"-Marker inside the rhombus? I have already seen that symbol without any marker...

BPMN uses two symbols for XOR gateways:

They are identical in meaning. We always use the version with the X because it seems less ambiguous.

Parallel Gateways

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Suppose that now we want a salad on the side. If you want salad no matter what, you could model it as we have done in
this diagram:
Hover over orange symbols for explanation

choose recipe prepare salad cook pasta eat meal

pasta

hunger desired
noticed dish?
3 minutes 10 minutes 15 minutes 20 minutes
steak

cook steak

10 minutes

The total of the task times equals the running time of the process, which was a total of 48 minutes for pasta and 43
minutes for steak. Congratulations: you've just analyzed your first process based on key data!
Still, this means waiting 23 or even 28 minutes until you can start to eat. Insufferable! You're really hungry, but what can
you do? Maybe you don't prepare the salad first and then cook the pasta or the steak, but you work on both at the same
time - in parallel. The appropriate symbol is the parallel gateway, or the "AND gateway" for short, as shown in here:
Hover over orange symbols for explanation

Choose recipe Cook pasta Eat meal

Pasta

hunger Desired dish? Hunger

noticed satisfied

3 Minutes 15 Minutes 20 Minutes

Steak

cook steak

10 Minutes

prepare salad

10 Minutes

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Diagramming tasks as parallel does not make simultaneous processing compulsory. In contrast to the example shown
before, it is also not imperative that you prepare the salad before starting other tasks. Parallel preparation does,
however, reduce our total time by 10 minutes. It is classic process optimization to make tasks parallel as much as
possible.

 Check yourself: What if we draw the same process, but leave the AND merge out for lack of space, and the path
from the "prepare salad" task leads directly to the XOR merge. What happens if we instantiate the process, and we
decide in favor of pasta?

The token is generated and then cloned as always at the AND split. As soon as we finish preparing the salad, the
token passes through the XOR merge and "eat meal" executes. Five minutes later,"cook pasta" also completes. Its
token passes through the XOR merge and "eat meal" executes again! That's not the behavior we wanted.

Choose recipe Pasta Cook pasta Eat meal

noticed
hunger Desired dish?

3 Minutes 15 Minutes 20 Minutes

Steak

cook steak

10 Minutes

prepare salad

10 Minutes

Data-based inclusive gateways

We want to make our process even more flexible: When we are hungry, we want to eat
Only a salad,
A salad and "something real," like pasta or steak, or
Only something real.
If you want a more compact representation, you can use the data-based inclusive gateway - the OR gateway for short:
Hover over orange symbols for explanation

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 15 minutes

choose recipe cook pasta eat meal

something real pasta

hunger desired desired dish?

noticed 10 minutes
components?
3 minutes 20 minutes
steak

cook steak
salad

10 minutes

prepare salad

Heads up! In practice, handling OR gateways is not as simple as these examples imply. It's easy to understand that
progress depends on waiting for another token to reach an OR merge. It can be harder to trace the synchronization
rules with complex diagrams that sprawl across several pages.

Event-based Gateways
We learned about the exclusive data-based (XOR) gateway option as a way to use different paths with regard to the data
being processed. Users of other process notations recognize this type of branching, but BPMN gives us another way to
design process paths: the event-based gateway - event gateway, for short. This gateway does not route based on data,
but rather by which event takes place next. To understand the benefit, consider the process shown below: We order
pizza and wait for it to be delivered. We can eat only after we receive the pizza, but what if the pizza doesn't arrive after 60
minutes? We'll make an anxious phone call, that's what! We can model this with the event gateway:
Hover over orange symbols for explanation

choose pizza oder pizza eat pizza

hunger pizza received hunger

noticed satisfied

call pizza
delivery service

60 minutes pizza received

As you can see here, not all intermediate events combine with the event gateway. You can, however, combine it with the
receive task.

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 ... ...

message

...

time

...

condition
...

signal
...

multiple

receive task ...

Events
Basic Concepts
Tasks and gateways are two of three flow elements we've come to know so far: Things (tasks) have to be done under
certain circumstances (gateways). What flow element is still missing? The things (events) that are supposed to happen.
Events are no less important for BPMN process models than tasks or gateways. We should start with some basic
principles for applying them. We already saw Start events, intermediate events, and end events. Those three event types
are also catching and/or throwing events:
Catching events are events with a defined trigger. We consider that they take place once the trigger has activated or
fired. As an intellectual construct, that is relatively intricate, so we simplify by calling them catching events. The point is
that these events influence the course of the process and therefore must be modeled. Catching events may result in:
The process starting
The process or a process path continuing
The task currently processed or the sub-process being canceled
Another process path being used while a task or a sub-process executes
Throwing events are assumed by BPMN to trigger themselves instead of reacting to a trigger. You could say that they
are active compared to passive catching events. We call them throwing events for short, because the process triggers
them. Throwing events can be:
Triggered during the process
Triggered at the end of the process
We can also model attached intermediate events with BPMN. These do not explicitly require waiting, but they do

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interrupt our activities, both tasks and sub-processes. Such intermediate events are attached because we position them
at the boundary of the activity we want to interrupt.
Hover over orange symbols for explanation

... task 1 task 2 ...

event 1
task 3 ...

A token running through the process would behave this way:

The token moves to task 1, which starts accordingly.
If event 1 occurs while task 1 is being processed, task 1 is immediately canceled, and the token moves through the
exception flow to task 3.
On the other hand, if event 1 does not occur, task 1 will be processed, and the token moves through the regular
sequence flow to task 2.
If event 1 occurs only after task 1 completes, it will be ignored.
Through BPMN version 1.2, with the exception of compensation events, attached intermediate events inevitably resulted
in canceled activities. BPMN 2.0 defines a new symbol: the non-interrupting intermediate event. It sounds awkward, but it
is useful:
Hover over orange symbols for explanation

... task 1 task 2 ...

event 1
task 3 ...

The token moves through the process as follows:

The token moves to task 1, which starts accordingly.
If event 1 occurs while task 1 is being processed, the token is cloned. Task 1 continues to be processed while the
second token moves to task 3, which is now also processed. This procedure may even take place repeatedly, that is,
the event can occur many times. Each occurrence results in another cloned token.
If event 1 does not occur, task 1 will be completed, and the token moves through the regular sequence flow to task
2.
If event 1 occurs only after task 1 completes, it ceases to matter.
In the following sections, we introduce the event types to be used when working with BPMN. We also explain how you can
react to different events using the event-based gateway.

Message
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Message
Sooner or later, most processes require communication, which can be represented in BPMN by means of the message
event. You'll recognize it as the small envelope. The meaning of "message" in BPMN is not restricted to letters, e-mails, or
calls. Any action that refers to a specific addressee and represents or contains information for the addressee is a
message.
Hover over orange symbols for explanation

choose pizza order pizza eat pizza

hunger pizza hunger

noticed received satisfied

 FAQ: Could I replace the task "order pizza" with a throwing message event?

Yes, you could:

choose pizza eat pizza

noticed
hunger ordered
pizza received
pizza satisfied
hunger

Heads up! We are not always happy with the throwing intermediate event. Implying a "send message" task without
modeling it explicitly can easily confuse inexperienced consumers of our models. We choose not to use throwing
intermediate events for messages and instead use a task. There are also special BPMN task types for sending and
receiving messages.

In the example below, we show a message leading to cancellation. In this scenario, we administer a web application.
When a user notifies us that the website does not work, we immediately search for the error. But maybe the user is
mistaken, and the website is fine. Maybe the user's Internet connection is defective. If the user tells us about the false
alarm, we cancel the search and swear at the user for wasting our time. If the error is actually found, however, we
eliminate it and simultaneously figure out who caused the error. If the user caused the error, we can swear at the user
for a different reason. If the user is not at fault, however, we thank him or her graciously for letting us know about the
problem.

search for bug fix bug thank user

no

user reports: users user thanked

"website fault?
is down!" yes

user reports:
"sorry, false insult user
alarm!"

user insulted

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Timer
The timer event is often used when working with BPMN because it is so flexible to apply. A clock icon represents the timer
event. The diagram below shows a few examples of applications:
working day

do morning
get up take bus to work ...
toilette

Monday-Friday 08 am
at 07 am
user support

check email view most handle most ...

inbox important topic important topic

every 2 coffee break

hours 10 minutes
holidays

choose book trip pack bags ...

destination

2 months 2 days
prior to trip prior to trip
Valentine 2010

wake beloved
get up buy bouquet with bouquet ...

02/14/2010 02/14/2010
08 am 09 am

Time moves on no matter what we or our processes do, so timer events can exist only as catching starts or intermediate
events.
You can model countdown times with an attached timer event. They are used this way frequently. You can specify upper
time limits - the maximum time allowed for a processing task - for instance:
Hover over orange symbols for explanation

choose pizza order pizza eat meal

hunger pizza hunger

noticed received satisfied

30 minutes

cook pasta

Non-interrupting timer events became possible with BPMN 2.0:

Hover over orange symbols for explanation

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 choose recipe prepare meal eat meal

hunger hunger
noticed satisfied
10 minutes prior
to completion

set table

Error
Do your processes run completely error-free? If not, you can identify potential errors in your models as a step toward
eliminating them, or as part of modeling escalation processes. In BPMN, error events are represented by a flash symbol.
The BPMN specification does not specify what an error may be. As the modeler, you have to decide that.
An error is a serious event in BPMN, so if catching, it can be modeled only as an attached intermediate event. This means
that an error during task execution must be handled in a specific way: As a throwing event, it can be modeled only at the
end of a process path so that the participant knows the process has failed. The parent process should likewise recognize
the failure.
You can find example of error events e.g. in the Implementation section for "Event Subprocesses".

Conditional
Sometimes we only want a process to start or to continue if a certain condition is true. Anything can be a condition, and
conditions are independent of processes, which is why the condition (like the timer event) can only exist as a catching
event. A process cannot therefore conditional event trigger a conditional event.
We can enhance our pizza process with conditions. If we want to have frozen pizza, the process starts as shown in the
diagram below. We take the pizza from the freezer and turn on the oven. But only after the temperature in the oven
reaches 180 C do we put the pizza in, and only after it is done do we take it out to eat.

take pizza from switch on oven put pizza in oven eat pizza
freezer

frozen pizza oven to 180° pizza hunger

desired ready satisfied

Signal
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Signals are similar to messages, which is why you can model them in BPMN as events just as you can with messages. The
symbol for a signal is a triangle. The essential difference between a signal and a message is that that latter is always
addressed to a specific recipient. (An e-mail contains the e-mail address of the recipient, a call starts with dialing the
telephone number, and so on.) In contrast, a signal is more like a newspaper advertisement or a television commercial. It
is relatively undirected. Anyone who receives the signal and wants to react may do so.

buy pizza eat pizza

pizza spot get an appetite evaluate pizza

seen on TV for pizza on pizzatest.de

We saw a new frozen pizza on TV, and we are keen to try it. The diagram above illustrates this new situation. We buy the
pizza, but we keep it in the freezer until we're really hungry for pizza. That's a conditional event. After trying the new pizza,
we go to Pizzatest.de to rate the new product. That's a signal. It is a signal for the general public too. (Pizzatest.de actually
exists, by the way, which proves again that you can find simply everything on the Internet!)

Termination
Let's look at the abstract example below. We already discussed (simple) Key Performance Indicator (KPI) analysis, and we
therefore know that this process always takes 55 minutes. After task 1, tasks 2 and 3 can be processed simultaneously.
Processing task 2 takes more time than does processing task 3, which is why it determines the runtime of the process. A
token that runs through the process is cloned in the AND split. The first token stays in task 2 for 45 minutes; the second
token stays in task 3 for 30 minutes. The second token arrives at the none event first, where it is consumed. After 15
more minutes, the first token arrives at the upper none event, where it is consumed too. Since no more tokens are
available, the process instance finishes after 55 minutes.

task 2

end 1

45 minutes
task 1

start
10 minutes
task 3

end 2

30 minutes

So far, so good, but what happens if we already know that, after having completed task 3, task 2 has become redundant?
This is a frequent situation with parallel task executions related to content. In such cases, we can apply the pattern
shown in here:
Hover over orange symbols for explanation

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 task 2

end 1

45 minutes
task 1

start

10 minutes task 3
no

task 2 no longer end 2

necessary?
yes
30 minutes

termination

Link
The link event is a special case. It has no significance related to content, but it facilitates the diagram-creation process. As
shown below, you can draw two associated links as an alternative to a sequence flow. Here, "associated" means there is a
throwing link event as the "exit point," and a catching link event as the "entrance point," and the two events are marked
as a pair - in our example by the designation "A."

... task 1 task 2 ...

A A

... task 1 task 2 ...

=

Link events can be very useful if:

You have to distribute a process diagram across several pages. Links orient the reader from one page to the next.
You draw comprehensive process diagrams with many sequence flows. Links help avoid what otherwise might look
like a "spaghetti" diagram.
Link events can be used as intermediate events only.

Compensation
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We execute tasks in our processes that sometimes have to be canceled later under certain circumstances.
Typical examples are:
Booking a train or airline ticket
Reserving a rental car
Charging a credit card
Commissioning a service provider
Below, we see this process: On Friday at 1 p.m. we agree with our partner either to go to the theater or to spend the
evening with friends. In both cases, we have to do something binding, either to reserve the theater tickets or make the
arrangements with our friends. When evening arrives, perhaps we no longer feel like going out at all. We then have to
cancel the arrangements we made with the theater or our friends before we can collapse in front of the TV in peace:

book theatre
arrange date carry out activity
tickets
theatre yes

Friday 1 pm planned Friday 6 pm still wanting

activities? to go?

friends no

arrange date cancel theatre

with friends tickets
theatre

what was
the plan?
friends

cancel friends

We can represent the latter part of the model more compactly with a compensation event, as shown in here:
Hover over orange symbols for explanation

arrange date book theatre carry out activitiy

tickets
theatre yes

Friday 1 pm planned Friday 6 pm still wanting

activities? to go?
cancel theatre no
tickets
friends
watch TV

arrange date cancel

with friends activitiy

cancel friends

There are special rules for handling compensations:

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 Throwing compensations refer to their own processes, so the event is effective within the pool. This shows how this
event type differs from a throwing message event.
Other attached events can take effect only while the activities to which they are attached remain active. In contrast,
an attached compensation takes effect only if the process triggers a compensation and the activity to which the
compensation is attached successfully completed.
Attached compensation events connect to compensation tasks through associations, and not through sequence
flows, which would otherwise be common usage. BPMN thus emphasizes that compensations are beyond the
regular process sequence; executing one is an exception.
The obligatory compensation task is a special task type that we explain with other task types in TODO

 Best Practice: Using Compensation Events

This example may be too simple to illustrate how much work this construct can save you. If you think of the complex
business processes that frequently require compensations, however, you'll see how much leaner your models can
be. You'll also be quick to spot the circumstances that demand compensations. We use compensation events only
occasionally to describe complex processes.

Multiple
We can use the multiple event to summarize several events with a single symbol. The diagram below applies the multiple
event to our pizza scenario. In the example, we try a new pizza after having seen it on TV or after a friend recommended
it. After eating it, we will rate the pizza on Pizzatest.de and in turn inform our friend if we also recommend this pizza.
Hover over orange symbols for explanation

buy pizza eat pizza

pizza comercial crave pizza pizza on
seen on TV or fri pizzatest.de
end evaluated and
recommended link sent to friend
pizza

Best Practice: Avoiding Multiple Events

You have to decide if multiple events serve your purposes. We concede their benefit in rough functional process
descriptions, but they cease to be as useful in the more advanced technical-implementation phase. You can't afford
to leave relevant details hiding in the descriptive text. We don't find the multiple event to be intuitive, nor is it helpful
on a functional level. It may make your diagrams larger to model all events separately, but the resulting diagrams will
be both more comprehensive and more comprehensible. The bottom line is that we have never used this symbol in
practice, nor have we seen anybody else doing so.
The model in here describes the same process, but the events are fully modeled:

pizza commercial evaluate pizza

seen on TV on pizzatest.de
buy pizza eat pizza
crave pizza

friend send evaluation

recommended to friend
pizza

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Parallel
The parallel event was added in BPMN 2.0 to supplement the multiple event. While a catching multiple event has XOR
semantics - it occurs as soon as one of its contained events occurs - the parallel event uses AND semantics. It doesn't
occur until all of its contained events occur. Because the throwing multiple event already implies AND semantics, the
specification defines parallel events as catching events only.

Escalation
The BPMN 2.0 specification added the escalation event. Mainly, it shows communication between parent and sub-
processes. We discuss it in here TODO with the help of an example.

Cancel
You can use the cancel event only in the context of the transactions.

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