4.4.3 Parent-child-relation

The following exercise shows that using parent-child-relations has a substantial impact on usability and flexibility of a model.

Child-elements are referenced to parent-elements and depend on them. This is why a change to a parent also changes the child accordingly.

You can also say that child-elements are associated with parent-elements.

Associativity ensures that the structure of a model or assembly is kept when changing dimensions (e.g. a through-body hole stays through-body; a cylindrical key stays concentric to its respective hole).

The following example explains the issues that can occur with missing or wrong association:

Open the model eltern_kind_beziehung (owning user: uebung_et).

RMB-click the rectangular pocket within Part Navigator and choose Information.

The window Information pops up. Here you can check which elements are defined as parents or children. (refer figure "Information")

The usage of parent-child-relations will be clear after changing the positioning of the rectangular pocket.

All elements referenced to the Rectangular Pocket are repositioned as well. Elements, that do not have a child-relation with the Rectangular Pocket, stay at their current positions. (refer figure "Positioning before")

Open Part-Navigator alt .

RMB-click Rectangular Pocket and choose Edit Positioning.

Click Edit Dimension Value. Select the vertical measurement 60mm and enter 50mm. You can leave the second dimension as it is.

As you can see, by repositioning the rectangular pocket, all referenced elements are repositioned with it.
The red hole stays in its position, since it is referenced directly to the Block, while the yellow hole is moved with the Rectangular Pocket.

NX shows parent-child-relations in the Part Navigator. Highlight an entry, and parents will be displayed red, childs will become blue. (refer figure "Parent child in NX")

You can change the Order of features in the Part Navigator, if you do not alter parent-child relations. Dragging a child above it's parent in the part navigator produces an error.

Additionally, the change in position can lead to a false rendering of the edge blend. (refer figure "Positioning after")

In this exercise you learned how child-elements depend and are referenced to parent-elements. This is why a child is also affected accordingly when editing its parent.

Note that when deleting a parent, the child is deleted as well!