[Nml-wg] UML modelling tools

Hi, As discussed at OGF-21 we should be using UML for modelling NML. Does anyone have recommendations for open source / free ware tools (e.g. ArgoUML) that all of us can use to read/update the UML? Is an open storage format that can be stored in version control a requirement for multiple people working on the same data model? Some of our European NREN partners have recommended Enterprise Architect (URL: http://www.sparxsystems.com.au/) Do any of you have any experience with this tool? regards, - anand.