The application layer is comprised of any number of digital vendors that support the functionality of your site, such as live chat, analytics, personalization, display advertising and more.
The data layer, which sits in the middle, transfers visitor interaction data occurring at the experience layer to vendors at the application layer.
The experience layer is the most visible. It is where the user interacts and engages with the your web site or mobile app.
One of the main functions of tag management is to easily map the data collected during the interactions on your web, mobile, and other digital channels to digital marketing vendors who need this data to provide a better customer experience. When a data layer is properly defined, tag management systems can easily ensure that a product name is conveyed to your web analytics provider in the same way it is to your affiliate tracking system.
A well-constructed data layer can act as both a common dictionary for your supporting digital marketing applications and a unifying road map for how you want to communicate with your customers. Without a model for how to think about your customer interaction data, you cannot unite your applications around common definitions. The data layer represents the promise of omnichannel marketing that many digital marketers strive to achieve.