DSDL being renamed to MDTS -- Modular Document Type Specification.

Schema language is a transformation: input plus output validation report.

Two kinds of language: validation only; validation plus PSVI.

PSVI changes in XML Schema are not new -- e.g. default attribute info in DTDs -- but to a different degree.

Schemas considered harmful? Benefits of no schema -- analogy to relational db, can't do anything without tables (schema); not true of xml schema.

Validation includes: structure, datatypes, integrity, other rules.

Integrity checks under-represented at present.

Open: "Allow all that is not forbidden" Closed: "Forbid all that is not allowed"

Useful to mix.

Schema language is a 'firewall' -- intermediary between set of all possible instances, and those that are desirable.

History of schema languages

Examples of applying the different languages