Talk:Web Science/Part1: Foundations of the web/Domain Name System/Tree structure

Information from the video
DNS – tree structure

DNS is a tree like data structure. If we will map all bunch of domains we would see a tree. And this is a computer science tree- with the root of the tree at the top and branches down at the bottom.

For example: google.com

At the top we have “com” and then below is “google”. And if we have www.google.com then “www” goes below “google”. The same with www.yahoo.com.

There can be more layers than only 3. For example within google we have one of the mail servers: aspmx.l.google.com. So what we have now – from top to bottom we see “com”-> “google”-> “l”-> “aspmx”. We have 4 layers.

Not only “com” can be at the top. For example, for some university with web site www.ucsd.edu we have: “edu”-> “ucsd”-> “www”. For computer department of this university - www.cs.ucsd.edu: “edu”-> “ucsd”-> “cs”->“www”.

Or another example: www.bbc.co.uk we have: “uk”-> “co”-> “bbc” ->“www”.

There are many places where individual names might repeat: “www” in yahoo is not the same as “www” in google. The whole point of each domain name is to uniquely identify a particular location in the tree. But what we have is not a tree yet. We must connect : “com”-> “google”-> “l”-> “aspmx”

“edu”-> “ucsd”-> “cs”->“www”

“uk”-> “co”-> “bbc” ->“www”

So “com”, “edu” and “uk” has a root named “.”(dot, but pronounced root). So “.” – is the root of DNS hierarchy and we go to each domain within that.

Let’s look here and see where the domains are. For example: “google”-> “l”-> “aspmx” is a google.com-domain name. The “google” identifies the top of the domain, but it’s underneath “com”, which is underneath “. (root)”. We also have yahoo.com-domain, ucsd.edu –domain, bbc.co.uk-domain.

But we also have smaller domains like l.google.com-domain or even aspmx.l.google.com- domain.

Finally there are some big domains (all of .com or .edu or .uk). But the biggest includes everything – the entire domain hierarchy itself.

--Jane Kruch (discuss • contribs) 21:47, 3 November 2013 (UTC)