Some of the language in WS-MEX seems to assume that @Dialect and @Identifier uniquely define a single metadata "blob". For example, in the description of PutMetadata it says:

"The resource metadata (identified by the dialect and identifier) specified by each metadata section MUST be replaced in its entirety by the metadata specified in the PutMetadata request message."

In general, however, this is not true. For example, it is permissible to split one's schema into separate xsd:schema files/documents - each having the same @targetNamespace. If you did a GetMetadata with a Dialect that specified @Type='xsd:schema' and @Identifier='http://www.foo.com' (for example), you may get a Metadata document with more than one MetadataSection's - each with the same @Dialect and @Identifier values. The spec says nothing about whether these sections are related to one another or about how/if they should be combined. On a PutMetadata operation, it's not clear which of the matching MetadataSections should be replaced or if all of them should be replaced. Similarly on the DeleteMetadata operation; which MetadataSection should be deleted or all?