Modular refactoring possible?

[eluser]Tom Vogt[/eluser]
I'm running an old-school PHP application that consists of about 65,000 LOC with a lot of database stuff going on.

One of my devs has proposed moving to Zend Framework. I've wanted to move to CI a while ago, but decided that with available ressources, a refactoring effort would not be manageable.

Now in ZF, according to the dev, it would be possible to keep the existing application and switch it over piece-by-piece, e.g. by creating models for just a few database tables, then using calls to those models instead of calls to our current slim abstraction layer, etc.

Now I'm wondering whether such an approach would be possible with CI. Can I move my app over piece-by-piece, while keeping it running at all times?


Or, as a simple starter: Can I call CI models from a non-CI application? Can I launch views? Or would the controllers have to be the place to start any refactoring?