The Assembly definition for each asset must be saved as a separate Maya .ma or .mb file. (A Maya file can contain only one assemblyDefinition node.)
To create an assembly definition
For example, a Locator representation is added to the assembly definition by default unless you turn off Add Locator representation.
An assembly definition node is added to the scene and appears in the Outliner represented by a file icon . For information about assemblyDefinition node attributes, see assemblyDefinition.
(Optional) You can now add Cache and Scene representations to the assembly definition. See Add assembly representations.