The files available here are in DBDesigner4 format. DBDesigner4 is a schema drawing program released under GPL.
The database schemas have been put together by Alberto Giampani, Dario Toledo and Isaac Cueto. We are also discussing a means of creating them automatically from the new XMLDB definitions with an XML transform.
Discussion of the database schemas happens either in the forum of the relevant module, or in the General developer forum.
Web view of the Moodle 2.8 schema and a downloadable Moodle 2.8 schema by Marcus green can be opened by MYSQL Workbench tool. Which was reversed engineered using moodle_local-sqlgenerator.