Kalpasutra/Vedanga?

[Gregory Goode]

In the PANCADASI, 1 vol, translated and commentated on by Swami Swahananda
(Ramakrishna Math), there is the mention of Kalpasutras.

Sloka IX.27
===========
  Such rituals and methods of worship have been collected
  and co-ordinated in the Kalpasutras.  With their help
  man, who has faith, may practise them without further
  enquiry.

  Swami Swahananda's commentary:
  Kalpasutras, six in number, are compiled by Jaimini,
  Asvalayana, Apastamba, Bodhayana, Katyayana and
  Vaikhanasa.  They are a Vedanga.

What is a Kalpasutra?  What is a Vedanga?

--Greg