Versions & Diff Viewer

Version snapshots

Each commit produces an immutable version snapshot — append-only, written atomically:

• First commit: the original upload is snapshotted as v1, and once the write has landed the new file is snapshotted as v2.
• Each subsequent successful commit produces v{n+1}.
• Snapshots are stored at {dataDir}/models/{id}/versions/v{n}.ifc.

Diff panel

The "Diff" toolbar button opens the comparison panel:

1. Choose a base (v1 / v2 / …) and a target (a version or current).
2. Click "Compare": green = added, yellow = modified, red = removed.
3. Click an entry to locate the element; modified entries expand to field-level old → new.
4. "Clear" resets the coloring.

Diff semantics

• GlobalId is the entity identity: added / removed are guid lists; changed is field-level old → new over direct attributes and pset attributes.
• Based on ifcdiff, run with only the attributes / property relationships; entity reference attributes (ObjectPlacement, Representation and other geometry-representation layers) are not compared — no geometric diff is currently provided.
• Removed elements no longer have geometry in the current XKT, so they only appear in the red list (design decision).
• When both base and target are immutable versions, the result is cached at versions/diff-{base}-{target}.json; target="current" is not cached.

For the endpoint contract see IFC Editing API.