A friend of mine doesn't have much experience on 3-Tier applications design and development and he would like to broaden his knowledge on this subject. Can you point me to good online resources or books on it? It would be great if they started from the principles. I was thinking of this tutorial as a good starting point.
What resources do you best like?
You could have a look at
http://dotnetslackers.com/articles/aspnet/Three-Tier-Architecture-With-ASP-NET.aspx and http://weblogs.asp.net/bsimser/archive/2006/08/13/3_2d00_tier-architecture-wtih-asp.net-2.0.aspx
MSPress have quite a few books for the .NET MCP Exams as well that would cover this.
You can look inside this site... https://stackify.com/n-tier-architecture/#:~:text=N-tier%20architecture%20is%20also,functions%20physically%20and%20logically%20separated.
He might want to start with the following book:
Fundamentals of N-Tier Architecture (.NET 2.0)
And then look at the following book for more up-to-date info:
WCF Multi-tier Services Development with LINQ
Book cover http://ecx.images-amazon.com/images/I/51ckQayArLL._SL500_AA240_.jpg
I don't have the impression the link you mention is telling something about 3-tier (or N-tier). Maybe you are mixing the definitions of N-layer and N-tier? These have different meanings.
A very good explanation about N-tier can be found on this site: What is N-Tier architecture?.
N-layer is not the same, but I would start by understanding N-layer before examining N-tier. Since the link you mentioned is ASP.NET, I think the tutorials on using layers in ASP.NET 2.0 and ASP.NET 3.5 found on Imar.Spanjaars.com are very interesting.
The very right place for you is the series of articles written by Imar Spaanjaars. You can find the series here and here.
http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=476 http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=416
