Is there a standard file format for Physical Data Models Representations? And with that I mean files from where i can see graphically the relations between the data tables.
For example in my work we use 'Toad Data Modeler' to create physical data models from existing data bases. These files are XML with 'txp' extension. Because I can't use Toad anywhere (license cost $) I look how to export the model to other formats but the only option that it has is image, and that is problematic because I cannot search text in and image, and for big databases is impossible to find something fast.
If that file format doesn't exist, is there at least some kind of defacto standard that can be interpreted from multiples software?
There is no such standard, unfortunatelly, for Entity Relationship Model.
There is some work to create a standard for UML with XMI.
By the way if your problem is that Toad Data Modeler is proprietary you can use the freeware version. Maybe it'll be enough to fit your needs.