AccdbMerge is a software application for the Microsoft Windows operating system. The application is built using .NET Framework. The application includes both graphical user interface (GUI) and command line executables.
When you perform the 'Open database' action, application connects to your database and reads information about database objects: definitions of tables, queries, modules and so on. Reading is performed using the Microsoft Access primary interop assembly which uses Microsoft Access COM object under the hood. This means that in order to open a database it runs your database in Microsoft Access and uses Microsoft Access to get information about object definitions.
After completion of reading, if the application has other-side database loaded then it re-compares lists of database objects and updates counts on the Home tab. After objects merge, the application also connects the database, re-reads objects and re-compares with other-side database.
By default, data processing is performed using Access database engine and does not require Access execution. However, if database engine is not available, or if you need to run queries that depend on other objects and can run only in Access (for example, query uses some module function) - then application may switch to 'Use DB Engine from Access application' mode, or you can switch to this mode yourself using corresponding toolbar button. In this case, the application launches an instance of Microsoft Access for each data processing task.
Unlike GUI, command line is using Access database engine to read database objects and process data. That's because communication with Access needs to be done in user interaction mode, and this is possible only for the GUI application. Command line tools are often used without user interaction, they can be triggered by the scheduler or some other process. Access database engine does not force MS Access execution, it is just set of libraries installed on the computer.
As a result, command line can access only objects available via database engine, it can not process most of programming objects available for the GUI (forms, modules, etc.). Command line can be used primarily for the data processing tasks.
