Cope and Drag

Cope and Drag (or CnD) is a lightweight diagramming language designed for use with the Forge lightweight formal methods tool.

The key idea is that CnD starts with a meaningful default visualization. Each operation added refines it. For example, you can constrain spatial layout (e.g., child nodes in a binary tree below their parents), group elements (e.g., nodes representing related components in a software architecture), or direct drawing style (e.g., color nodes in a red-black tree based on their color).

The goal isn’t to create pretty diagrams but to generate useful ones. Diagrams respect the model’s structure and spatial relationships. If the diagram doesn’t match the model, no diagram is generated, and a solver-generated error is produced. This helps identify bad instances, where the model doesn’t match the author's intent, making CnD a meaningful debugging tool.

🔍 See our upcoming paper in ECOOP 2025.

Grounded In Cognitive Science

Cope and Drag is informed by findings from cognitive science about how people draw, interpret, and are confused by diagrams.

Spatial Relationships Matter

“Spatial thinking is the foundation of abstract thought” - Barbara Tversky

People read meaning into position - above, below, inside. Cope and Drag's constraints allow authors to shape diagram layouts to reflect these meaningful relationships. When spatial relationships in a diagram reflect domain relationships, they serve as cognitive aids. For example, placing a parent above its children in a family tree matches conveys a model of generational relationships, while nesting elements inside containers effectively shows membership.

These spatial choices aren't just aesthetic; they help convey the semantics of the underlying model more intuitively. By making these relationships explicit through layout, Cope and Drag helps create useful, domain specific visualizations.

Visual Differences

💡 In cognitive psychology, pre-attentive processing refers to how we perceive certain visual features—like color, size, and position—almost instantly, before focused attention.

Visual features like color, size, and position are processed by our brains almost instantly. Cope and Drag uses these features strategically to make diagrams easier to understand at a glance. Directives allow diagrammers to control how elements are displayed (color, shapes, or size), resulting in diagrams that focus the audience on what matters most.

Next Steps

• Getting Started: Install the tool, explore how it interfaces with Forge.
• Examples: Play with some pre-built example diagrams.