design vs agility

Just watched this.

Which decisions need to be made when re: architecture...

What is the cost to change later...

Some items that resonated with me - all quotes are not exact:

1. XP- Simplest thing that works is not the easiest, or the stupidist
2. Encapsulation /(using interfaces) to make decisions later. Create enough abstraction for things that are likely to be changed later ...
   
3. Domain model up front is worthwhile (David Farley)
4. Domain model already exists (it is at work everyday in the business), coders should faithfully try to replicate in code - Erik Doernenburg
   
5. Domain model = "Software simulation of the business model"
6. Key is to know when decisions need to be made..
7. Fred george- "If you want to make improvements, invest in making better programmers"

Ignoring non-functional requirements can be hazardous. (examples from Ian)