If you want to share a database, the best format to choose for export is iDatabase because it preserves the complete content and structure of the database, including pictures (here is a tutorial on how to export a database from iDatabase).
You can export a database in this format and then send it via email to a Mac user or to an iPhone user. The recipient, to be able to use this database, it will open it with a double click on a Mac, or with a tap on iPhone, as you would do with a normal file, iDatabase then will ask if you want to import it. Once the file has been imported, it can be used and edited as it does with the other databases in the app.
To send via email a large database, you have previously exported on a Mac, it's a good idea to compress it as a zip file before to send it.