Assembly Terminology

Assembly Terminology

Overview: There are five terms you must understand when working with assemblies: top-down, bottom-up, active component, loaded component, and design in context.

Top-Down

This type of assembly modeling allows you to create and edit component geometry (piece parts) at the assembly level. Since you create and edit in the assembly, you can take advantage of each existing component's geometry and location in the design of new component parts. All creating and editing done at the component level automatically reflects in the component's part file.

Bottom-Up

This type of assembly modeling implies that all of the individual part files (piece parts) in the assembly already exist. Bottom-up modeling is analogous to building a toy model, the pieces are already created, and you only need to assemble them.
When you edit an individual component part file outside of the assembly structure, the changes automatically reflect in each assembly structure containing the component.

Active Component

This is the component in which you create or edit geometry. When you are working in a component part, the active component is the same as the displayed component. When working in an assembly, you can make one of the components your active component. All other components become temporarily unavailable. The active component name becomes blue in the Specification Tree.

The active component is the part in which you are actually working. To make a part the active component, you can either select Edit | [ component ] object | Edit; double-click the component in the Specification Tree; or right-click the component in the Specification Tree and select [ component ] object | Edit.

All geometry is created in the active part. When you save a file, CATIA saves the active component and all child components of the active component. When the active component is an assembly (or subassembly), it is the file to which you add, remove, reposition, rename, and replace components.

Loaded Component

This is any open part. When an assembly file is opened, all of its components open when Load referenced documents is activated within the Tools | Options General, General dialog.

Design in Context

You have the ability to create and edit components while in the assembly. This is known as designing the part in the context of the assembly. This approach causes the change to occur simultaneously at both the assembly and the component level. In order to modify a component in the assembly file, you must first make the component active.