The focus on this chapter is how to extend the standard software without an over-layer. To those that come from Dynamics AX 2012 or prior, it may not seem a big issue: over-layering was the only choice, and when compared to other products in the space, it was one of its key features. When we over-layer, the system copies the code into the package's layer and the developer makes changes to this copy. It is all seamless and has worked well since Axapta 1.5.

The problem is when we need to service the application, such as deploying a hotfix, we will need to check for conflicts and potentially update our code. Also, if we have an ISV solution that over-layers a package, we will need an update from the ISV if the hotfix modifies an over-layered element.

The other downside of over-layer is that we can't have two ISV solutions that over-layer the same element. This has always been a problem, and it can only be solved by manually merging in a higher layer.

The solution Microsoft has for this is called extensibility. This is where we store the changes we want to make in a delta change format in a separate object. This means that two ISVs and the customer could all add fields to the SalesLine table, and not version-lock the customer. All of these fields are merged by the system, and the table will have all fields in all packages added to the table in SQL. There is no longer a need to have separate tables with the additional fields and code in order to avoid over-layering a table.