A rather basic question about DCS

Hello All,
 
Hello All! I am applying for a Process Control Specialist job  with a company dealing with Emerson products and I was wondering if you could help me answer one question on the online application form. The question is, " Describe the key elements of an overall DCS architecture"? I did some research and found a lot of information but I am not sure detailed the answer should be since this appears to me as a very broad question. Since you are the experts, I thought I will ask for your help!
 
Thank You!
 
Azmil ( Maskara )