Section 1.1: What Are Quality Engineering Sequence Diagrams?

A sequence diagram is a specialized form of interaction diagram that illustrates the flow of interactions between actors and systems. Among the three types of interaction diagrams—sequence, communication, and timing—sequence diagrams are the most widely utilized model in software development.

These diagrams clarify several key elements:

• Which actors are involved in the process?
• What are the initiators and responses to events?
• Who initiates the calls?
• What actions occur, and in what sequence?

Sequence diagrams can effectively describe workflows within software applications and can also outline organizational processes. As organizations mature, these diagrams can support various methodologies, including Value Stream Mapping, Capabilities Mapping, Event-Driven Architecture, and Model-Based Development & Testing.

While standard notations like UML and BPMN exist, they often become unwieldy to manage at scale and may lack universal understanding. This is precisely where Quality Engineering Sequence Diagrams shine.

Section 1.2: The Simplicity of Quality Engineering Sequence Diagrams

Engineers sometimes complicate matters when simplicity is needed, and Quality Engineering Sequence Diagrams aim to counter this tendency. These diagrams are straightforward representations that:

• Illustrate the flow of interactions between actors and systems.
• Identify the sequence of initiators, responses, and messages.
• Highlight key information for consideration.

Quality Engineering Sequence Diagrams capture interactions across two dimensions: the flow of activities and their order in time (without duration). They include:

• Actors involved in the interaction.
• Vertical lifelines for each actor.
• Activation events.
• Flows between actors.
• Annotations for important contextual information.

While additional elements could be incorporated to specify flow types (synchronous vs. asynchronous, manual vs. automated), maintaining simplicity is paramount. The goal is to clearly specify processes with minimal effort to enhance the quality and speed of feature implementation or process changes.

Section 2.1: Enhancing Quality with Sequence Diagrams

One of the significant challenges for software teams with diverse expertise is finding a common language for deliverables. Teams can waste hours drafting extensive specification documents, which often lead to ambiguity rather than clarity.

Immediately following the definition of a Quality Engineering User Story, sequence diagrams can be crafted for each identified case, serving as a lightweight pivot for cross-functional teams. Quality Engineering Sequence Diagrams contribute to quality by:

• Being result-oriented, focusing on specific deliverables per scenario.
• Applying systematically to all user stories and process definitions.
• Being scalable across teams, processes, and easily maintainable.

Section 2.2: Accelerating Speed with Sequence Diagrams

Another drawback of lengthy documentation is the time scarcity that organizations face as they strive for transformation. Speed in Quality Engineering resembles a continuous marathon of sprints, where quick, iterative increments must be delivered while maintaining momentum.

By concentrating on a common deliverable for each software increment, teams can establish a rhythm of iteration that can be sustained and expanded across the organization. Quality Engineering Sequence Diagrams facilitate speed through:

• A focus on common diagrams that highlight essential elements.
• Establishing a rhythm that creates a shared ritual for specifying key software flows.
• Favoring asynchronous collaboration through a standardized format.
• Providing a visual representation of process flows for enhanced visibility.

Section 2.3: Implementing Quality Engineering Sequence Diagrams

The gradual implementation of diagrams can be tailored to the maturity level of different teams. Key principles to encourage quality at speed include:

• Communicating the rationale behind the adoption of these diagrams.
• Defining a template format for replicability and sharing.
• Systematizing the approach by leveraging Definition of Ready (DoR) and Definition of Done (DoD).

To create each Quality Engineering Sequence Diagram, follow these steps:

1. Set the Objectives: Start by validating the necessity for a diagram. Clearly articulate the objectives at the top of the diagram to streamline focus.
2. Identify the Scope: Determine the processes and actors that will populate the horizontal and vertical axes of the diagram. Keep one diagram per process to maintain clarity.
3. Map Step-by-Step Interactions: Identify flows within the process, beginning with initiating triggers that kick off the flow. Each trigger should start a new interaction, ensuring all flows are represented accurately to prevent oversight.
4. Add Emphasis on Information: Enhance your diagram by including pertinent information that aligns with your objectives. Use notes to clarify details about actors, triggering conditions, flow execution, and error management.
5. Step Back to Improve the Process: Critically review the completed diagram to assess its effectiveness. Techniques like gap analysis, "what if" scenarios, and reality checks can help refine the process.

References

• Martin Fowler, Kendall Scott (1999). UML Distilled: A Brief Guide to the Standard Object Modeling Language, Second Edition. O'Reilly.
• Sanford Friedenthal, Alan Moore, Rick Steiner. A Practical Guide to SysML, Third Edition.
• The Systems Modeling Language, The MK/OMG Press.
• Lambert M. Surhone, Miriam T. Timpledon, Susan F. Marseken (2010). Sequence Diagram, VDM Publishing.