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World Congress 2026 Europe - Virtual Stage • Jul 2, 2026 • Session details

How We Waste Time Building APIs — and the Moment DDD Starts to Matter

Jacek Milewski

Are innocent feature requests silently destroying your team's autonomy? Discover how applying Domain-Driven Design at the exact right moment rescues leaking API architectures.

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#1 about 5 min

Building the initial training planner API

How early system design choices manifest as strategic decisions in API development.

#2 about 2 min

Why cloning services creates architectural duplication

The consequences of forking repositories to support isolated business tickets.

#3 about 5 min

Coupling services to handle cancellation fees

How adding business rules to operational endpoints creates tight coupling and misplaced responsibilities.

#4 about 3 min

Recognizing crossed service boundaries in systems

Understanding the negative impacts of teams making isolated decisions that cross domain boundaries.

#5 about 6 min

Applying domain-driven design principles to APIs

Using bounded contexts and capability layers to evaluate architectural boundaries.

#6 about 6 min

Defining boundaries for planning and booking

Separating the strategic training planner from the operational resource booking context.

#7 about 4 min

Using simulations to test system architecture

Generating hypothetical scenarios to uncover hidden requirements and missing domain concepts.

#8 about 3 min

Prioritizing feature implementations based on cost

Deciding when to support new system capabilities by analyzing likelihood and future complexity.

#9 about 4 min

Making clean architecture decisions iteratively and rapidly

Minimizing delivery overhead by stabilizing small architectural decision records.

#10 about 5 min

Aligning context relations with team topologies

Using the open host service pattern and streamlined teams to clarify API responsibilities.

#11 about 3 min

Modeling event economics and financial logic

Ensuring business logic resides in the service that owns the financial decision, not just the data.

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1:22 min

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4:33 min

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