Foundation Series: Business Process Modeling

Business Process Modeling

Business Process Modeling (BPM) allows us to increase our understanding of business processes and improve communication with stakeholders and implementation teams. Business analysts will create diagrams that represent business processes. These diagrams can be used to elicit requirements, define scope, and improve communication within the team.

We use diagrams because they are intuitive. Diagrams can provide us with an easy to remember and understand visualization of a business process. These diagrams are a type of object oriented analysis (OOA) diagram. A BPM describes a business process, where an entity-relationship (ER) diagram describes business objects. The example in the previous link is an ER diagram.

A Simple Process Model

The easiest way to get a high level understanding of a business process model is to review the diagram for a simple process.
The following diagram represents a customer withdrawing money from their bank account. The customer convinces the bank that she is allowed to withdraw money, then requests the money, which the bank provides (after confirming that it is available). The customer then terminates the transaction.

The diagram does not show exceptions to the process, like having the wrong password, or not having enough funds in their account. Business process models can absolutely demonstrate these situations, and many others. We’ve kept this process simple, as it is an introduction to the concept.

The BPM Example Diagram

Swim Lanes and Pools

The first thing you will notice about the diagram is that all the activities happen in one of two areas, labeled customer and bank. These two areas are called pools. While that seems like a silly name, there is a reason for it. There is a type of diagram called swim lanes, designed to show how different people or entities interact. Each person gets a swim lane in which all of her actions happen. In BPM, all of the swim lanes for a single company are grouped together in a pool. In our example, each pool has a single lane.

In our diagram, there are two pools - one for the customer, and one for the bank.

Flow Objects

Our diagram includes examples of three flow objects: events, activities, and gateways. Events are represented as circles. We have starting events (triggers) at the top of the diagram and ending events at the bottom. Activities are drawn as rounded rectangles. An activity can be a single task (like “confirm logout”), or they can represent an entire sub-process. Our simple example shows only tasks.

Gateways represent points in the process where the flow can separate or combine. The diamond is the symbol used to represent a gateway - and it is common to see it in a flow chart, showing how a decision can cause a process to go in one of two directions. The two examples in our diagram show flows combining, with a “+” symbol inside the diamond. This implies that both inputs are required for the process to continue. For example, the steps “Deliver Cash” and “Update Account Balance” must both be completed before the sytem can “Receive [the] Logout Command”.

Sequence Flow

The solid arrows that connect all of the items within each pool are called sequence flows. They represent the flow of the process from one flow object to the next. Notice that there are no sequence flows from one pool to another. These solid arrows can cross swim-lane boundaries within a single pool, but never across pool boundaries. Since our example has a single swim lane in each pool, we don’t see this.

Message Flow

The dashed arrows that cross the pool boundaries are called message flows. A message flow represents communication between two entities. In our example, the customer sends a message to the bank asking for $100. The bank sends a message to the customer in the form of $100.

A Lot More

There are a lot more details to BPM. We’ve left them out to keep the introduction simple (and “brief”).

BPMN Standard

There is a standard notation to use in business process modeling, called BPMN. Business Process Modeling Notation is the industry standard for drawing diagrams. By using the same notation, every diagram becomes easier to read. All of the official documents can be found at www.bpmn.org.

This site has tutorials, the official standard (BPMN 1.0 [Feb 2006]), and other documents. There is even a visio stencil (Visio 2003, Visio 2002, Visio 5) that can be used to draw diagrams consistently with a minimum of fuss.

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Check out the index of the Foundation Series posts which will be updated whenever new posts are added.

This article was published on Tuesday, July 18th, 2006 at 9:15 pm and is filed under Business Process Modeling, Requirements, Requirements gathering.
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