Using topic and assembly - starting from article?

Dear all,

can someone give me a steer about this...

I currently have a collection of standalone documents, each is a
DocBook <article> .

I want to organise these into a more structured form, particularly so
that I can get them all to come out in a single PDF document (grouped
into super-topic chapters/sections...).

The topic and assembly elements in DocBook 5.1 look ideal for that
purpose. Is that correct?

If yes, how can I move from <article> to <topic>? I want one article
to become one topic, I don't need to chunk them into smaller parts.

Could I simply replace <article> by <topic> in each xml file and
nearly everything will work without further editing?

Thanks, Phillip