Constraint (computer-aided design)¶

A declared geometric or dimensional relation that a parametric CAD model must preserve during editing.

Version: v2 · 2026-09-19 · History
Domain-specific #: 3862
Domain group: Applied Sciences & Engineering
Origin domain: Engineering & Design (beyond software)
Subdomain: Computer Aided Design → Engineering & Design (beyond software)

Core Idea¶

Dimensional and geometric constraints, driving and reference dimensions, local and assembly constraints and under-, fully- and over-constrained states must be distinguished. A solver converts relations among model entities into equations or predicates and updates degrees of freedom while maintaining the satisfiable constraint set. The abstraction is therefore identified by a declared carrier, a transformation or constraint over that carrier, and an invariant that tells an analyst whether the named structure is genuinely present.

The load-bearing residual is not the broad topic of computer aided design. It is the domain-specific identity fixed by the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit.

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Drawing Rules That Stay True

When you draw on a computer design program, you can add rules to your drawing, like 'these two lines always stay side by side' or 'this line is exactly 5 long.' If you drag one part, the computer moves the other parts so the rules stay true. Those rules are constraints.

Rules That Hold a Design Together

In computer-aided design (CAD), a constraint is a rule about how parts of a drawing or model relate. Some rules are about sizes, like 'this edge is 10 cm long,' and some are about shapes, like 'these lines are parallel' or 'this circle touches that line.' The software keeps all the rules true when you change something. A drawing can have too few rules (parts can still wiggle), just enough (everything is locked in place), or too many (the rules fight each other).

Solver-Maintained Design Relations

In CAD software, constraints are relationships you place on geometry: dimensional constraints set sizes and distances, and geometric constraints set relationships such as parallel, perpendicular, tangent or coincident. A solver turns these relationships into equations and adjusts the model's remaining freedoms, called degrees of freedom, so that all constraints stay satisfied. A sketch can be under-constrained (some freedom left), fully constrained (none left), or over-constrained (conflicting or redundant rules). Designers also distinguish driving dimensions, which control the shape, from reference dimensions, which just report a measurement. Constraints can apply within one part or between parts in an assembly.

In computer-aided design, a constraint is a relation among model entities that a solver maintains as the model is edited. Dimensional constraints fix sizes, distances and angles; geometric constraints fix relations such as parallelism, tangency or coincidence. The solver converts constraints into equations or predicates over entity parameters and updates the remaining degrees of freedom so that the constraint set stays satisfiable. The model's state is classified as under-, fully- or over-constrained, and driving dimensions (which control geometry) must be distinguished from reference dimensions (which only report it). Constraints can be local to a sketch or part, or assembly constraints between components. A complete description specifies the CAD system and version, entities and parameters, constraint types and values, degrees of freedom, solver conventions, the dependency graph, satisfiability state and behavior under edits.

Scope of Application¶

Constraint (computer-aided design) belongs to computer aided design and is useful where the analyst can specify the typed computer aided design carrier, including its objects, relations, parameters, conventions, evidence, and comparison cases, then evaluate the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit. The scope is broad within that domain but bounded by the need for the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit. The entry records a descriptive analytical identity; practical use requires the governing domain's evidence, standards, and safety obligations.

Clarity¶

The abstraction clarifies a crowded vocabulary by making the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit the center of the account. A claim should name the carrier, the governing operation or relation, the applicable assumptions, and the recognition test.

Manages Complexity¶

Without the abstraction, an analyst must reason directly over many local details: the carrier roles, admissibility assumptions, competing conventions, derived invariants, boundary cases, and proof or validation obligations specific to Constraint (computer-aided design). Constraint (computer-aided design) compresses them into the roles in the structural signature. That compression permits comparison across instances without erasing the variables that determine validity. It also exposes which details may be varied safely and which are constitutive.

Abstract Reasoning¶

Identify the carrier. State what the elements, states, objects, or observations are: the typed computer aided design carrier, including its objects, relations, parameters, conventions, evidence, and comparison cases. Reject examples whose alleged carrier belongs to a different problem.
Lock the constitutive rule. Express the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit independently of one notation or implementation.

Knowledge Transfer¶

Knowledge transfers strongly among subfields of computer aided design because they reuse the typed computer aided design carrier, including its objects, relations, parameters, conventions, evidence, and comparison cases, A solver converts relations among model entities into equations or predicates and updates degrees of freedom while maintaining the satisfiable constraint set., and type the carrier, state every parameter and convention in the definition, test that the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits are explicit, compare the nearest accepted identity, and report counterexamples, uncertainty, and limiting cases.

Relationships to Other Abstractions¶

Current abstraction Constraint (computer-aided design) Domain-specific

Parents (1) — outgoing typed relations

Constraint (computer-aided design) is a kind of Constraint Prime

It remains its own entry because its identity is fixed by the CAD system and version, entities and parameters, constraint type and value, degrees of freedom, solver convention, dependency graph, satisfiability state and behavior under model edits.

Hierarchy path (1) — routes to 1 parentless root

Constraint (computer-aided design) → is a kind of Constraint

Neighborhood in Abstraction Space¶

Constraint (computer-aided design) sits in a crowded region of the domain-specific corpus (17^th percentile for distinctiveness): several abstractions share nearly its structure, so a description that fits it tends to fit its neighbors too.

Family — Engineering Design & Systems Modeling (39 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25