With the Fall 2019 update, Microsoft converted all legacy C/AL code into AL objects. Currently, the big application monolith has been split into two apps:

• System application: with approximately 200 objects.
• Base application: depending on the localized version, it spans from 6,000 to 8,000 objects.

To be extended, these need to be referenced as dependencies in the app.json file, and their symbols pulled on-premises or from an online sandbox through the AL: Download symbols AL Language command.

When pulled in the .alpackages folder, they are typically referenced through a version number in the major, minor, build, and revision notations, and this is reflected in the name of the symbols that are downloaded (for example, Microsoft_System Application_15.0.36560.0 and Microsoft_Base Application_15.0.36626.36918).

The major version digit typically corresponds to the Dynamics 365 Business Central major update release.

The October 2019 (or Fall 2019) release update is major version 15. The Spring 2020 (or April 2020) update release will be major version 16, and so on.

The minor version typically corresponds to minor updates. The November 2019 update 1 is minor version 15.1, December 2019 update 2 should be minor version 15.2, and so on.

The build number is a progressive number that is incremented by Microsoft as soon as there are changes committed to the branch that is related to feature enhancements or bug fixing.

When developing an extension, you must be aware of what system and application object level is needed as a minimum requirement, as defined in the dependency parameter of the app.json file.