Projections

A projection slices an instance along a type axis: instead of one big diagram containing every atom of every type, you render one sub-diagram per atom of a chosen type (a "sig"). Projections are how you visualize trace-like, state-indexed, or time-indexed data without the diagram collapsing into noise.

Projections are specified in the top-level projections: block of a .cnd file.

Syntax

projections:
  - sig: State
    orderBy: "next"
  - sig: Time

Each entry has:

Field	Required	Description
sig (or type)	yes	The type / sig to project over. One sub-diagram per atom of this type.
orderBy	no	A selector whose tuples define the ordering of atoms of sig. Typically a next-style relation for trace data.

Shorthand: a bare string is interpreted as just sig.

projections:
  - State       # equivalent to { sig: State }

What happens

When a projection is active, CnD:

1. Enumerates the atoms of sig (ordered by orderBy if given).
2. For each atom, builds a filtered copy of the instance where the sig atoms are restricted to that one.
3. Renders those copies as multiple panes — the user selects which atoms to show at a time from the sidebar.

The multi-pane rendering is driven by MultiProjectionGraph and the projection filtering itself by alloy-instance/projection.ts.

Interacting in the UI

Open the Projections sidebar control in the Graph view (or Edit view). It lists every projected sig and lets you multi-select atoms: each selection adds a pane.

Worked example

From demos/gc/gc.cnd, projecting a garbage-collector trace along State:

projections:
  - sig: State
    orderBy: "Initial->Changed + Changed->Marked + Marked->Swept"

The orderBy selector specifies the transition edges, so CnD lays the panes out in the correct phase order: Initial → Changed → Marked → Swept.

Interaction with other top-level blocks

• Projections compose with temporal mode: a temporal model with projections shows both time steps and projected sig atoms, as separate axes.
• Projection filtering runs before constraints: and directives: are applied — each projected sub-instance is laid out independently.