Another small amendment to the svn-book

[Flemming Bjerke]

For me, it was a bit difficult to understand when to use subversion because I 
did not really understand the principle. I, and probably many others, would 
have helped quite a lot if you in the introduction had a subsection 
called: "When and when not to use Subversion"

Probably, you can make this subsection much better. Feel free to do it. But, I 
think it is important to explain to newbies when Subversion is good, and why 
it is not good for everything.

Flemming Bjerke 

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When and when not to use Subversion

Subversion should be used if you have good reasons saving old versions of 
files. One good reason is of course that it is important for you be able 
return to former versions of your files, e.g. you need to be able to find 
deleted files or parts of files. Another good reason is when you are several 
person who share some files and you all change them. Subversion will help you 
keeping record of the changes others (and yourself) have made so you can act 
correctly when such changes have been made.

But, everything has its price. Since subversion keeps track of changes, it has 
to be told when changes happen. Therefore, you cannot copy, mv, rename etc. 
among your subversion files in the normal way. You have to use the special 
svn commands to do such things. You also need to have a svn repository where 
all the old versions are saved. But, that repository is not readable for 
humans. If the repository is damaged, you risk to loose old version of your 
files. Therefore, it is important that you back up the repository. You may 
use the hot-backup.py script as described in this book.

An example illustrates the point. You would like have your datafiles on your 
laptop and your home-pc syncronised. In many cases, you don't care about 
older versions of the files. Therefore, you should use a much simpler 
syncronisation program like unison that has no special repository and allows 
you to do all the normal file manipulations. But, if it is important for you 
to have old versions of certain files (if you write articles, a book, 
software, or whatever) then it is probably a good idea to make a 
svn-repository for these files at your home-pc (or at a server) so you can 
check relevant versions out from your laptop, and your home-pc as well.