The xml file contains the entity / table + mappings definitions but not the data? This is different as sometimes people want to use an XML file as their database and if you want to use your xml file as your database, that's not going to work.
It is possible, but not supported out of the box, to have an xml file with definitions of entities, mappings and meta-data and import that to entity definitions, table definitions and mappings between them. You have to write a custom plugin to import your xml file and then add entities, tables etc. in your plugin. This isn't as simple as it sounds and requires some deeper knowledge of the inner workings. We have planned an import framework for v3 but it's not done yet.
So short answer: no today this isn't possible. With a lot of work from your side you can make this work, but IMHO it's easier to reverse engineer the database you have.