You can start writing an application in either the front-end or the back-end. If you start with the front-end, you design the screens and forms first, using mock data. If you start with the back-end, you create your data store up front, and then you can create your front-end later. This is what you’ll do with the Guestbook application.
A persistence layer and a service layer make up the bottom layers of your back-end. You’ll persist guestbooks and their entries to a database. Your service layer calls your persistence layer, providing a buffer in case you wish to swap out your persistence technology later.
Figure 1: Service Builder generates the shaded layers of your application.
Service Builder is Liferay’s code generation tool for defining object models and mapping those models to SQL databases. By defining your model in a single XML file, you can generate your object model (the M in MVC), your service layer, and your persistence layer all in one shot. At the same time, you can support every database Liferay DXP supports.
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