Package & Model & Project & Overlaying & Extension in Dynamics 365 ERP

//Dynamics 365

//Directory for XML file
/AosServices/PackageLocalDirecotry/

Packages:

Packages (Model store) are deploy-able solutions that have inter-dependencies with other packages. Package are same as model store in ax 2012. In ax 2012 it is DB, In Dynamics 365 for finance and operations is in DLL file. New package may refers to multiple existing package

Model:

Each model must be belong to any one of package. Model to package is always having one to one relation.

Projects:

Each model can consists of multiple projects. But one same projects can't be access in 

another Model. If developer wants to access multiple model elements from different model,

then needs to do proceed with  multiple project.

Overlaying:

Overlaying is when you modify existing code by changing the system behavior.

For example:

1) overlaying the Method on the Table. Right click on the object and click Customize.

2) Developer wants to attach new work-flow in Std. Form means, then have to go for overlay customization. (Note this can be achieve in extension also, for reduce upgrades, Migration, Merging code)
3) Over Laying - Customization in Base Package

Extension:

Extensions are used in Dynamics 365 for operations much more flexible. Extensions allow you to leave the system behavior, but adding your piece to it. In some cases you have to overlay but try

to avoid that if possible. As overlaying may seem simple but it will cost you on upgrades, hot-fixes, maintaining code and merging code. Extension will save in separate XML file.
Extension based on customization in Separate Package.

Overview of overlaying and Extensions:

Screenshot: