SYSML21 — Textual notation cannot carry element identity, severing round trips with the repositories the specification's own API defines

Nature: request for enhancement (interchange gap). Severity: significant.

The textual notation deliberately omits Element::elementId: text is treated as a projection, and identity as the repository's concern. But the notation is the form engineers version, diff and review, and the Systems Modeling API and Services specification addresses every element by that id. The combination severs round trips: any tool that serializes a model to text and reads it back has lost the correlation with the repository it came from, so a rename – same element, new name – is indistinguishable from a delete plus a create. Implementations are already inventing workarounds (sidecar mapping files, IRI conventions, comment conventions), none of which survive interchange through another conforming tool.

Proposal: standardize identity annotations – either a normative metadata library, or dedicated surface syntax if the taskforce prefers. A minimal library form, implementable today because user-defined metadata is already conforming notation:

standard library package IdentityMetadata {
    metadata def ElementId {
        attribute id : ScalarValues::String;
    }
    metadata def ProjectRef {
        attribute projectId : ScalarValues::String;
        attribute branch : ScalarValues::String[0..1];
        attribute org : ScalarValues::String[0..1];
    }
}

Applied opt-in: @ElementId

on an element pins its repository identity; one @ProjectRef on the root namespace binds the document to a project (branch selecting a version, never contributing to identity). Elements without an annotation keep tool-derived identity, so unannotated models are unaffected and annotation cost is paid only where correlation matters.

Implementation experience: OpenSysML (github.com/Open-MBEE/OpenSysML) implements exactly this shape: the metadata library, a validation pass (duplicate and malformed ids, project-scope conflicts), RDF export keyed by the effective id, and reader re-materialization closing the notation -> RDF -> notation round trip byte-for-byte – all without any specification change, demonstrating that only the standardization of the spelling is missing. Round-trip measurements against a live Flexo MMS repository are maintained in the project's committed interoperability report.