Never use descriptors as components to represent a BOM’s labor content.  DBA is not designed for this and it is not compatible with the cost rollup or actual job costing architecture.  

The notion of component labor only exists because some light manufacturing systems advocate it as a work-around solution for their lack of routings.  Even so, component labor is not viable in any form because it is not calculated from cycle times and has no ongoing maintenance capability and is not practical for widespread use.  

Routing sequences, on the other hand, are ideally suited for labor and overhead costing because they are based on setup hours and cycle times that are automatically costed at work center hourly rates and added up through all your labor processes.  Routings are based on settings that are practical to maintain on a widespread basis.  Besides costing, routing sequences provide process documentation for guidance out on the shop floor and also provide the basis for work center scheduling.