Hi guys, I've built a web application which basically logs work that has been done upon projects plus maintain resources used etc. What I need now is to set it up so that projects can be billed. Billed such that - each task that has been undertaken in a project is regarded as a billable service.

Instead of building my own invoicing system and accounts management system I was wondering if there was any standard data format i.e in xml DTD or so to which I could set up the information so it could be imported by a third party accounting system for billing - or if not then what is the best way to accomplish this.

I need to integrate invoicing capabilities somehow - better if its third party as I don't wish to have to go through building an entire accounting system.