CSCI927 - Service-Oriented Software Engineering Week 3

Business Process Model and Notation (BPMN) is a widely-used standard for representing and analyzing business processes in a graphical format. It bridges the gap between business process design and implementation, making it an essential tool in the toolkit of service-oriented software engineering (SOSE). In this week’s post, we’ll explore the basics of BPMN, its key components, types of activities, events, gateways, and the concept of tokens.

What is BPMN?

BPMN stands for Business Process Model and Notation. It is a standardized graphical notation that allows businesses to document, model, and understand their processes in a clear and concise way. BPMN is particularly valuable because it is designed to be understood by all business stakeholders—business analysts, technical developers, and process participants alike.

Why BPMN is Important

In the realm of SOSE, BPMN plays a crucial role in the design and orchestration of services. By modeling business processes using BPMN, organizations can visualize the flow of activities, identify inefficiencies, and ensure that all aspects of the business process align with organizational goals. This is particularly important in service-oriented environments where multiple services interact with each other in complex ways.

Key Components of BPMN

BPMN diagrams are composed of several core elements that represent different aspects of a business process. These include:

• Flow Objects:
  • Events
  • Activities
  • Gateways
• Connecting Objects:
  • Sequence Flows
  • Message Flows
  • Associations
• Swimlanes:
  • Pools
  • Lanes
• Artifacts:
  • Data Objects
  • Groups
  • Annotations

Types of Activities: Tasks and Subprocesses

Activities in BPMN represent the work being performed within a business process. They are primarily categorized into tasks and subprocesses.

Tasks

A task is a basic unit of work that cannot be broken down further within the process context

Subprocesses

A subprocess is a compound activity that encapsulates a set of tasks, providing a way to simplify and manage complex processes.

Types of Events: Start, Intermediate, and End

Events in BPMN represent things that happen within a business process. These events are divided into three main types:

Start Events

Start events initiate the process flow. Types include:

• None Start Event: A simple start with no specific trigger.
• Message Start Event: Triggered by the receipt of a message.
• Timer Start Event: Begins the process at a specific time or after a defined period.
• Conditional Start Event: Triggered when a condition becomes true.
• Signal Start Event: Responds to a broadcast signal that can trigger multiple processes.

Intermediate Events

Intermediate events occur between the start and end events, affecting the flow of the process:

• Catch Event: Waits for a trigger (e.g., message, timer, signal) before proceeding.
• Throw Event: Generates a trigger that can influence the process or other processes.
• Timer Intermediate Event: Introduces a delay or specifies timing within the process.
• Message Intermediate Event: Indicates a point where the process sends or receives a message.
• Error Intermediate Event: Handles errors that occur during the process.
• Escalation Event: Used to indicate an escalation in a process, typically signaling a higher priority action.

End Events

End events signify the completion of the process. Types include:

• None End Event: Marks the simple end of a process.
• Message End Event: Sends a final message when the process ends.
• Error End Event: Indicates that the process ended due to an error.
• Terminate End Event: Ends the entire process immediately, regardless of other ongoing activities.
• Signal End Event: Broadcasts a signal that other processes can respond to.

Types of Gateways

Gateways control the divergence and convergence of the process flow. They represent decision points, where the process can take multiple paths. Types of gateways include:

• Exclusive Gateway (XOR): Allows only one of several paths to be taken, based on conditions.
• Parallel Gateway (AND): Allows multiple paths to be taken simultaneously.
• Inclusive Gateway (OR): One or more paths can be taken based on conditions.
• Event-Based Gateway: Directs the flow based on an event that occurs.
• Complex Gateway: Combines multiple types of decision criteria, allowing for more advanced control.

The Concept of Tokens in BPMN

In BPMN, the concept of a token is used to represent the flow of control within a process. A token is an abstract representation of a process instance moving through the model. When a process is initiated, a token is created and it moves through the sequence flows, activities, and gateways.

• Token and Activities: As the token moves through an activity, it represents the execution of that activity.
• Token and Gateways: When a token reaches a gateway, the type of gateway determines how the token will proceed. For example, an exclusive gateway will allow the token to pass through only one of the available paths, while a parallel gateway will split the token into multiple tokens, one for each path.

The movement of tokens through a BPMN diagram helps visualize how a process flows from start to end, including how decisions and parallel activities are handled.

BPMN in Action

Let’s consider a simple example: an order processing system in an online store. Using BPMN, you could model the process starting from the customer placing an order, followed by order validation, payment processing, and finally, order fulfillment and delivery.

1. Start Event: The process begins with the customer placing an order.
2. Task: The system validates the order to ensure all information is correct.
3. Gateway: A decision is made whether the payment is successful.
4. Task: If successful, the order is sent to the warehouse for fulfillment.
5. End Event: The process concludes when the order is delivered to the customer.

This simple diagram provides a clear and visual representation of the order process, making it easy to understand and analyze.

BPMN and SOSE

In SOSE, BPMN can be used to model the interactions between various services within a system. For example, in a service-oriented architecture, you might have services for customer management, order processing, inventory management, and shipping. BPMN allows you to model how these services interact, where the dependencies are, and how information flows between them.

This not only helps in the design phase but also in monitoring and optimizing the processes once they are implemented. By using BPMN, you can ensure that your service architecture is aligned with business processes and is capable of adapting to changes in business needs.

Lecture 3