Top-down or Bottom-up are the two most common design styles. I don't know
how much detail you are looking for, but here are some simple explanations.
Bottom-up means to design each part of an assembly separately. This may be
when you don't have Intralink and several designers are working on what will
eventually be the same assembly. Each part is created individually and then
'merged' together into an assembly. This is when you find out how well the
pieces fit together.
Top-down, however, is where each piece is created at the assembly level. I
can't speak for anyone else, but that's how I have always designed even back
on the boards (I just didn't know it actually had a name!). Each piece is
constructed inside the assembly and them 'pieced out' to their respective
detial 'parts' (.prt).
Hope that helps
Top down design is where the functionality of an entire component
module, or product, is considered simultaneously, rather than just as the
sum of it's parts. High power workstations make this possible as entire
assemblies can be easily manupulated and the overall effect of design
changes noted. It's important to think 'top down, bottom up' when doing
this, which is to say, allt he parts in an assembly must either own their
own geometry, or have it fed in by the assembly, and not reference other
parts in the assembly. This is because, unless you really know your stuff,
you can end up creating circular references galore, leading to
Top-down design as I know it, is a process where design information is
passed down from the top level to lower levels. Portions of the design can
then be assigned to multiple designers with reference information included,
which will then update if changes are made at higher levels.