A Photoshop template gives the underlying structure to the data-driven graphics. The template not only contains the visual design for the graphics, it also houses the variables you fill in with data. When you design a template, plan to set aside a layer for each variable you need.
I'll use the example of building coupons from a list of products and their prices, and the images that go with them. Each coupon must contain the coupon background (which won't change) and also a layer for each of the variables that will change for each coupon, which are the product name, its price, a picture of the product, and whether it was grown organically (Figure 20.1).
Figure 20.1. My template (left) contains top and bottom bars that won't change, along with layers for the variables. In the Layers palette for this template (right), I grouped the template and variable layers separately, for clarity.