Application object layers hold everything that is displayed in the Application Object Tree (AOT). This topic describes application object layers and how they are used in Microsoft Dynamics AX.
Layers are a hierarchy of levels in the application source code that enable you to make modifications and additions without interfering with the application objects in the next lower level. When you make an object modification on one level, the modification overshadows the object on a lower level. You could, for example, decide to add e-mail information to a standard form. The addition would be saved on your level only. The revised form replaces the standard form. However, you can always return to the original form at the next lower level by removing the new form.
Three customer groups have an interest in adding and modifying application objects:
Application developers who create the standard application.
End users of Microsoft Dynamics AX.
The following table describes the application object layers in Microsoft Dynamics AX.
The standard application is implemented at the lowest level, the SYS layer. The application objects in the standard application can never be deleted.
When the application is modified to match country/region specific legal demands, these modifications are saved in a separate layer, the GLS layer. If an application object, for example, a form, is modified in the GLS layer, the modifications are saved in the GLS layer only and the modified version of the form is used.
HFX is an application object patch layer reserved by Microsoft for future patching or other updates. For more information, see Application Object Patch Layers.
SL1, SL2, or SL3
A layer where the distributor can implement vertical partner solutions. SL is an abbreviation for SoLution.
When a business partner creates their own generic solution, their modifications are saved in the BUS layer and the top level application objects are used.
Value Added Resellers (VAR) can make modifications or new developments to the VAR layer as specified by the customers or as a strategy of creating an industry specific solution. Such modifications are saved in the VAR layer.
The supervisor or administrator of an end-user installation might want to make modifications that are generic to the company. Such modifications are saved in the CUS (CUStomer) layer.
End users might want to make their own modifications, such as in their reports. These modifications are saved in the USR layer.
Each layer is saved in a separate file that is named Ax<layer>.aod, for example, Axsys.aod for the SYS layer, Axsl1.aod for the SL1 layer, and so on. The .aod extension is an acronym for Application Object Data.
In addition to the 10 layers, most layers also have a patch layer. For more information, see Application Object Patch Layers.