Design Requirements
Motivating design requirements for the schema language with the default query language binding include:
1. Represent abstract patterns such as the head+body pattern.
2. Support progressive validation.
3. Include assertions or abstract rules from an external file.
4. Support a one-to-one mapping between the natural-language statements and artificial-language statements.
5. Support the generation and labelling of arcs between information items.
Motivating design requirements for the schema language with the default query language binding do not include:
Simple specification of constraints that are simply expressed by grammar-based validation, such as Part 2 (RELAX NG) schemas or DTDs.
Replacement of any other standard schema language for XML.
Single-pass or streamable implementation.
As well, certain outcomes are out-of-scope for this part of ISO/IEC 19757:
Specification of a type system.
Generation of links between multiple occurrences of some datum across multiple documents for the purpose of consistency-checking.