This is my little endorsement to this tool
really usefull to extract uml from an existing PHP project. In GNU/Linux system (actually Bsd world too) there is at least Umbrello which read and write XMI format.
I am not expert of MS Windows world I just tryed googling it, I found this: http://www.altova.com/umodel/xmi.html . Umodel is 149$ software, it look like a very complete software, it could worth the price, but actually I prefer to keep code as simple as it could be catched just looking at the code, classes/methods names and little documentation, but sometime you loose control of the code.
I also tried autodia, that state an experimental support for importing xmi format to dia format. This is really experimental, starting from the missing strict dependence: libxml-simple-perl is required it you want to do:
$ autodia -l umbrello -i project.xmi getting handlers.. getting pattern for umbrello AutoDia - version 2.14(c) Copyright 2003 A Trevena using language : umbrello ..using Autodia::Handler::umbrello opening Ebaysync.xmi Not an ARRAY reference at /usr/share/perl5/Autodia/Handler/umbrello.pm line 87.
Thus … experimental.