Hi Javier,
you need to add a database node in the Domain Model tab of your dataservice project and configure it with the connection of your persistent database. Refer to the "Connecting the Database" online lesson at this link https://my.webratio.com/learn/learningobject/connecting-the-database-v-80 to learn how you can connect the database.
For further information about the synchronization refer to these online lessons:
- https://my.webratio.com/learn/learningobject/domain-model-synchronization-importing-the-database-v-80
- https://my.webratio.com/learn/learningobject/domain-model-synchronization-exporting-the-domain-model-v-80
- https://my.webratio.com/learn/learningobject/domain-model-synchronization-manual-mapping-v-80
Best regards.