Schema-based metadata editor (MDE): to ensure highest quality data through conformance. Lightweight client, Web 2.0. Builds on ten years of previous editor experience. It has emerged that users wanted editor with conformance, usable in their browser (no installation).
Generic metadata editor: cross-browser, generic to schemata. Schema driven, where the schema includes validation constraints. Help as floating messages. Cannot enforce a persistence mechanism, because that is app-specific. Nesting of elements. Live validation.
Web server supports the embedding application, the application calls MDE. MDE talks to Service Provider Interface via a broker, to fetch the metadata record given the record identifier (from the application); and MDE talks to the metadata schema repository to get schema.
Schemas are typically in XSD, which are is normalised and contain embedded schemata. Normalisation and flattening require preprocessing, so they use the MSS format as a type of flattened XSD. Reuse encouraged with documentation and reference implemention.
Why not XForms? Not very user friendly.
Available at metadata.net. To do: add element refinements; implement encoding scheme support; provide ontology and thesaurus tie-in.