Editing Product lifecycle (section)

===Bottom–up design===
Bottom–up design (CAD-centric) occurs where the definition of 3D models of a product starts with the construction of individual components. These are then virtually brought together in sub-assemblies of more than one level until the full product is digitally defined. This is sometimes known as the "review structure" which shows what the product will look like. The BOM contains all of the physical (solid) components of a product from a CAD system; it may also (but not always) contain other 'bulk items' required for the final product but which (in spite of having definite physical mass and volume) are not usually associated with CAD geometry such as paint, glue, oil, adhesive tape, and other materials.

Bottom–up design tends to focus on the capabilities of available real-world physical technology, implementing those solutions to which this technology is most suited. When these bottom–up solutions have real-world value, bottom–up design can be much more efficient than top–down design. The risk of bottom–up design is that it very efficiently provides solutions to low-value problems. The focus of bottom–up design is "what can we most efficiently do with this technology?" rather than the focus of top–down which is "What is the most valuable thing to do?"