Reference path decomposition

[TRThurman]

Summary

This issue proposes additions and clarifications to the EXPRESS-Q specification based on formal analysis comparing the specification against implementation requirements and architecture documentation.

Identified Gaps

1. Incomplete EBNF Grammar

The current grammar in express-q.ebnf is missing several constructs that are documented in the specification prose:

• Inverse navigation operator (<-): Documented in symbols table but not in EBNF
• Constraint blocks ({}, \!{}): Documented but grammar only shows []
• Alternative blocks (()): Documented but not in EBNF relationship production
• Required path blocks (<>): Documented but not in EBNF
• Supertype constraint (||): Documented but not in EBNF
• Aggregate index ([i], [n]): Documented but not in EBNF
• Line continuation (\): Documented but not in EBNF
• Enumeration literals (.VALUE.): Not documented at all

2. Missing Constraint Expression Grammar

The specification states:

constraint_expression = ? expression following EXPRESS syntax ?

This is incomplete. Need formal grammar for:

• Comparison operators (=, <>, <, >, <=, >=)
• Boolean operators (AND, OR, NOT)
• String literals ('value')
• Enumeration literals (.TRUE., .MAXIMUM_MATERIAL_CONDITION.)
• Attribute paths (entity.attribute)

3. Missing Operator Precedence

No explicit precedence rules for combining operators in complex reference paths.

4. Missing MAPPING_OF Template

Cross-module reference substitution via /MAPPING_OF(entity)/ is used in practice but not documented.

5. Negative Constraint Logic Rules

The \!{} operator is documented but no rules for:

• Logical interaction with positive constraints
• Contradiction detection
• Satisfiability requirements

Proposed Changes

1. Extend EBNF grammar with complete operator coverage
2. Add formal constraint expression grammar
3. Add operator precedence table
4. Document MAPPING_OF template syntax
5. Add negative constraint validation rules

References

• ISO 10303-11:2004 — EXPRESS Language Reference Manual
• ISO TC 184/SC 4 N2661 — Guidelines for the Development of Mapping Specifications
• Mapping Spec Validator formal analysis documentation

[TRThurman]

This is a todo eventually.