Cross-cutting Concepts (X)

What the layer describes

The X layer answers the question “What conditions, choices and uncertainties concern the architecture?”. It brings together explicit concepts, each linked to its subjects in the other layers. The layer is not a category for unclassified elements.

Concepts and how they relate

A requirement (Requirement) is a need or condition that an architecture element satisfies. The element that fulfils it realises the requirement, through the “realises” relationship (realisation); the source of the relationship is any element. A constraint (Constraint) restricts architecture options, and an assumption (Assumption) is a planning statement awaiting confirmation or revision.

An architecture decision (ArchitectureDecision) records a choice, with its context, options and rationale. An architecture exception (ArchitectureException) records a bounded deviation from a requirement or a constraint. The “is associated with” relationship (association) connects any two elements, for example a decision with the elements it concerns.

A risk (Risk) is an uncertainty with a possible effect on the architecture or on the results of the service (PublicService). It affects the exposed elements, through the “affects” relationship (affects). Elements from OPS and CNT mitigate the risk, through the “mitigates” relationship (mitigates). One example is the disaster recovery plan (DisasterRecoveryPlan).

A geographic area (GeographicArea) describes a jurisdiction or the coverage area of a service, not a hosting location. As an element of the location family, it aggregates the services it covers, through the “aggregates” relationship (aggregation).

Element types

The layer has 9 element types, in these families: information (2), intent (5), decision (1), location (1). Each type's own fields are listed under its definition; the fields common to every element are described under the core concepts.

• RequirementRequirement · intent family

  A need or condition that an architecture element is expected to satisfy.

  Key attributes: kindprioritystatusversionownersourceReferencesplanningContextrequirementKindstateacceptanceCriteriaderivedFromrefinessatisfiedBy
• ConstraintConstraint · intent family

  A restriction that limits possible architecture choices.

  Key attributes: sourceversionownersourceReferencesplanningContextstaterationaleappliesTovalidFromvalidUntil
• ArchitectureDecisionArchitecture decision · decision family

  A recorded choice, its context, options and rationale.

  Key attributes: statuscontextdecisionconsequencesversionownersourceReferencesplanningContextrationaleapprovedByapprovedAtaddressesappliesTobasedOnrespectsselectedOptionselectsstatesupersedes
• AssumptionAssumption · intent family

  A proposition used in planning that needs confirmation or review.

  Key attributes: versionownersourceReferencesplanningContextstaterationalereviewDateappliesTo
• RiskRisk · intent family

  An uncertainty that may affect architecture or service outcomes.

  Key attributes: likelihoodimpacttreatmentowner
• ComplianceAssessmentCompliance assessment · information family

  An assessment of how a subject meets specified obligations or requirements.

  Key attributes: subjectagainstresultassessedOnevidence
• GeographicAreaGeographic area · location family

  A jurisdiction or service coverage area, distinct from a hosting facility.

  Key attributes: levelnutsOrLauCode
• EvidenceEvidence · information family

  A cross-cutting record supporting a claim, assessment or decision.

  Key attributes: versionownersourceReferencesplanningContextkindreviewStateartifactReferencesourceVersionproducercapturedAtreviewedByreviewedAtlimitationssupportschallengesdocuments
• ArchitectureExceptionArchitecture exception · intent family

  A recorded, scoped departure from a requirement or constraint.

  Key attributes: versionownersourceReferencesplanningContextstatedeviatesFromscoperationaleapprovedByapprovedAtvalidFromexpiresAt

In the “Family support benefit” example

Figure 4.12 (page 42) shows the X layer in the example. The architecture decision “ADR 1: assisted intake” keeps assisted paper intake alongside the channel (ServiceChannel) “Public benefit portal”, from ORG. The recorded reason is that a digital-only path would fail during a portal outage. The decision is associated with the fallback procedure (FallbackProcedure) “Assisted paper intake”, from CNT.

The risk “Risk of unreconciled paper cases” concerns duplicate or delayed decisions after manual intake of applications following an outage. The recovery plan “Benefits technical recovery”, from OPS, mitigates the risk.