Basic Development concept AX7

Before we talk AX7 Development, we need to have look at few terminologies, which are as under

Element: Element is any Object residing in AOT. E.g. any Base Enumeration, any EDT, any Table, any Form, which you see in AOT Tree, is an element itself.

Model: A Model is a group of elements. A model is collection of elements that represent a distributable software solution.

Packages: A package is deployable unit, which may have multiple Models.

Project: Projects are the logical containers for everything that's needed to build your application. A project can be associated with only one model.

After we know basic terminologies, which will be used very frequently, let’s start with ways of developments AX7 provides.

With arrival of AX7, now we can do development in AX, with two methodologies.

1. OverLayring
   If you have been developer of previous versions of AX such as AX2012 or AX2009, you don’t need explanation of this way of development. Name of this methodology ‘OverLayring’ is self-explanatory.
   In Microsoft Dynamics AX, a layer system is used to manage elements. The USR layer is the top layer and the SYS layer is the bottom layer, and each layer has a corresponding patch layer above it.
   OverLayring means if you do change/customize any element in upper layer, it will override its definition, in lower layer.
   This is what we were doing till AX2012 to customize AX. It basically allows customization of metadata and source code in higher layer. For example, you can add a new field in CustTrans Table in the user layer or in ISV Layer.
2. Extension
   It refers to concept of extending existing elements, without overriding those into other layers. That means, elements will not be customized, instead elements will be extended. This approach reduces upgrade cost and conflicts. By creating extension elements, all of the customizations and code are stored in a separate assembly. It only contains the code that was added or changed in the extension file. Since this code resides in a separate assembly, it improves performance and the ability to upgrade and test.