4D Database Applications are comprised of many file parts. One of the major files for a 4D Database Application is the 4D Datafile (.4DD). This file contains the data for an instance of the 4D Database application from the created records for the tables and fields defined in the database.

Many data files can be created from one database application. For example, there could be a default data file, a test data file, and the actual deployed data file. To make things more seamless when deploying a 4D database, an associated data file is remembered in the cached files. This allows the database to open and not request a data file to be selected.

For built applications, this feature can be applied in one of two ways, based on the full path of the built application or based on the application name. In most cases, there is no major difference between the two users. This function becomes more important if there is an intent to run multiple copies of the built application on the same machine.

Suppose the built application is set to be based on the application name. This is useful if there is potential for the users to change the name of the paths or install new copies of the application in different directories. However, if the database is copied and multiple instances are run, the subsequent applications will have the same name and cause a conflict when trying to open the same data file and will run in read-only mode.

To work around this, it would be better to set the application to link the data based on the full path of the application. There cannot be two files/paths on a machine with the same values, this will allow copies to have their own datafile and prevent the issue.