LEARN. PRACTICE. GROW.Concept and mechanism
A validation chain should identify what each layer establishes. Well-formed XML permits syntax interpretation; schema validation checks defined structure and types; registered constraints and guidelines add usage conditions. Passing XSD does not remove an MDR violation. External code lists are maintained separately and can change without a new message version. The page inspected on October 1, 2026 publishes the August 2026 edition, version 3. Recording the list actually loaded by each process, including caches, helps explain intermittent rejection. Cardinality and Choice also need interpretation: an alternative branch does not authorize populating every possibility simultaneously.
Guided application
In XML, an expanded name combines namespace URI and local name. A prefix is an alias bound to a URI rather than a version in itself. Different prefixes can represent the same element; the same local name can belong to different vocabularies. Tests should include alternative prefixes with the same binding, incorrect URI, cardinality violations, incompatible choices, and valid or invalid codes. Associate rejection with its concrete layer and rule. Avoid a generic invalid-schema response when failure occurred in a business rule or code cache. L3 support gains a reproducible diagnostic path when it knows artifacts and versions used for each execution.
Example: two instances use the same XSD but only one loaded the approved list. A load balancer makes rejection appear random; comparing in-memory versions and repeating per-instance tests scopes the cause.
Common pitfalls
Equal schema treated as equal configuration; prefix treated as complete identity; removed validation treated as repair; Choice treated as cumulative list.
Related topics: Semantics and contract documentation · Messages, headers, and states · Mapping and data integrity
Record layer, rule, artifact, and version for every validation result.
Reference: Implementation compliance checklist · DR ISO20022 fundamentals professional assessment2026.10