Application configuration files [closed]

YAML, for the simple reason that it makes for very readable configuration files compared to XML.

XML:

<user id="babooey" on="cpu1">    <firstname>Bob</firstname>    <lastname>Abooey</lastname>    <department>adv</department>    <cell>555-1212</cell>    <address password="xxxx">ahunter@example1.com</address>    <address password="xxxx">babooey@example2.com</address></user>

YAML:

    babooey:        computer : cpu1        firstname: Bob        lastname: Abooey        cell: 555-1212        addresses:            - address: babooey@example1.com              password: xxxx            - address: babooey@example2.com              password: xxxx

The examples were taken from this page: http://www.kuro5hin.org/story/2004/10/29/14225/062

First: This is a really big debate issue, not a quick Q+A.

My favourite right now is to simply include Lua, because

• I can permit things like width=height*(1+1/3)
• I can make custom functions available
• I can forbid anything else. (impossible in, for instance, Python (including pickles.))
• I'll probably want a scripting language somewhere else in the project anyway.

Another option, if there's a lot of data is to use sqlite3, because they're right to claim

• Small.
• Fast.
• Reliable.

Choose any three.

To which I would like to add:

• backups are a snap. (just copy the db file.)
• easier to switch to another db, ODBC, whatever. (than it is from fugly-file)

But again, this is a bigger issue. A "big" answer to this probably involves some kind of feature matrix or list of situations like:

Amount of data, or short runtime

• For large amounts of data, you might want efficient storage, like a db.
• For short runs (often), you might want something that you don't need to do a lot of parsing for, consider something that can be mmap:ed in directly.

What does the configuration relate to?

• Host:
  • I like YAML in /etc. Is that reimplemented in windows?
• User:
  • Do you permit users to edit config with text editor?
  • Should it be centrally manageable? Registry / gconf / remote db?
  • May the user have several different profiles?
• Project:
  • File(s) in project directory? (Version control usually follows this model...)

Complexity

• Are there only a few flat values? Consider YAML.
• Is the data nested, or dependent in some way? (This is where it gets interesting.)
• Might it be a desirable feature to permit some form of scripting?
• Templates can be viewed as a kind of configuration files..

XML XML XML XML. We're talking config files here. There is no "angle bracket tax" if you're not serializing objects in a performance-intense situation.

Config files must be human readable and human understandable, in addition to machine readable. XML is a good compromise between the two.

If your shop has people that are afraid of that new-fangled XML technology, I feel bad for you.