2. Architecture Constraints (MVP)

2.1 Organizational and Business Constraints

Constraint	Description	MVP Impact
Open Source License	Apache 2.0 license under Open Rail Association	All code publicly available and transparent
License Compatibility	All third-party dependencies must be compatible with Apache 2.0	Limits choice of libraries and frameworks
Development Timeline	Maximum 5 weeks development time	Simplified 3-context architecture instead of more specialized contexts
Team Size	3 backend developers	No frontend developer, file-based UI only
Multi-Company Collaboration	European railway companies (DB, SBB, ÖBB) might use PopUpSim	Architecture must be adaptable to different requirements
Big Bang Timeline Support	Must simulate 3-week Big Bang conversion periods	Performance requirements for time-critical operations
Single Site Simulation	One Pop-Up site with one layout at a time	Architecture focused on single-site efficiency
Microscopic Simulation	Individual wagons/resources modeling	Cannot use macroscopic or aggregate approaches
Workshop Operations Focus	Pop-Up workshop operations only	Cannot include general railway operations
Prototype Foundation	Reuse suitable components from 3-Länderhack 2024 prototype	Leverage proven SimPy approach

2.2 Technical Constraints

Constraint	Description	MVP Impact
Operating System Support	Windows, Linux, macOS	Cross-platform Python compatibility
GitHub Repository	https://github.com/OpenRailAssociation/dac-migration-dss-popupsim	Version control and collaboration platform
Python Backend	Python 3.13+ for backend development	Backend limited to Python ecosystem
SimPy Framework	Discrete event simulation engine	Event-driven simulation paradigm required
Deterministic Simulation	Reproducible results required	Enables reliable testing and layout comparison
File-Based Data	CSV/JSON input/output only	No database installation required
Matplotlib Visualization	Charts and graphs output	No web frontend in MVP
No Admin Rights	Installation without administrator privileges	Lightweight, self-contained architecture
Laptop Hardware	Must run on standard laptops (4GB RAM minimum)	Memory and computational complexity constraints
Offline Operation	Core functionality works without internet	Self-contained operation
Simulation Scale	Must handle up to 1,000 wagons	Memory management and algorithm efficiency
Code Format	PEP-8 with type hints, Ruff formatting	Python coding standards
Type Checking	MyPy type checking required	Code quality and maintainability
Testing Framework	pytest for all tests	Standardized testing approach
Documentation Format	Markdown for all documentation	Documentation toolchain standard
Architecture Documentation	Must use arc42 template	Standardized architecture documentation structure
Architecture Decision Records	Must document significant architectural decisions using ADRs	Maintains decision history and rationale

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