Constraint-based CAD assemblies: In modern, constraint-based modeling software, do assembly constraints (mates) explicitly create and maintain geometric relationships between the parts in an assembly?

Introduction / Context:
Assembly constraints (mates) are fundamental to parametric CAD. They position and orient parts relative to each other, reflecting real-world interfaces such as coaxial shafts, planar contacts, or fixed offsets. This question confirms that constraints are the mechanism that creates and preserves those relationships in the model.

Given Data / Assumptions:

• A parametric CAD system is in use (e.g., Inventor, SolidWorks, Creo, NX, Fusion).
• Parts are separate files inserted into an assembly file.
• Constraints can be edited and recomputed when geometry changes.

Concept / Approach:
Constraints encode geometric conditions: coincident, concentric, parallel, perpendicular, tangent, distance, angle, and more. When the geometry of a part changes, the solver recomputes constraint satisfaction and updates the assembly. This yields predictable behavior, motion studies, and interference checks.

Step-by-Step Solution:

Verification / Alternative check:
Suppress constraints temporarily and move parts freely; then re-enable constraints to see the system lock components back into their defined relationships. This demonstrates their control over geometry.

Why Other Options Are Wrong:

• Constraints are not cosmetic (option B); they are geometric rules.
• A BOM (option C) lists items but does not position them.
• Relationships are active during modeling, not only rendering (option D).
• Behavior is not random (option E); the solver is rule-driven.

Common Pitfalls:
Overconstraining assemblies; creating conflicting mates; referencing unstable edges rather than datums; ignoring subassembly structures that simplify constraint sets.

Final Answer:
Correct: constraints define and maintain inter-part relationships