En cada link segun la version de Moodle, tenes todas los DER de las tablas que conforman Moodle.
Development:Database Schema
From MoodleDocs
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 Databases forum.
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Moodle 1.8
http://moodle.org/file.php/5/moddata/forum/28/376698/moodle_1.8_data_structure.rar
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Moodle 1.7
http://moodle.org/file.php/11/moddata/forum/110/268325/db-edudist-Moodle-1.7_.rar
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Moodle 1.5.3
http://moodle.org/file.php/11/moddata/forum/110/267644/Db-Edudist-Moodle1.5.3-xml.rar