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Peppol Policies - strategic Peppol business goals that frames and are relevant to the Architecture.
Architecture Characteristics - high level characteristics for the architecture. These are non-functional requirements that are often non-measureable e.g. Architecture Characteristic “Scalable”.
Architecture Principles - Guardrails that that are guiding the Architeture design towards the Architecture Characteristics e.g. the Architecture principle “Scale out, not Up” supports the Architecture Characteristic “Scalable”.
Architecture Requirements - Functional requirements and Non-functional requirements that are measurable e.g. Functional Requirement “For a C4 it must be possible to change C3 because…….” or Non-Functional Requirements (measureable) like SLAs.