Database structures can be exported to an xml file. The xml file will contain the tables, fields, relations, and all attributes. Structure definitions can be exported through File->Export->Structure definition to XML file...
These xml files can be used to create new database applications in 4D through File->New->Database From Structure Definition... Clicking this will allow you to select the xml file. Once an appropriate file has been selected, select the location and name for the new structure.
Creating a new database from a structure definition allows the database to have all tables, fields, and relations; defined by the definition; automatically created in the brand new database.
Note: All forms, data, and methods are not exported. The xml file only contains information to the structure.