DevShed: Service Layers in PHP Applications (a Series)

DevShed has posted a series of tutorials talking about different sorts of service layers in PHP applications - seven of them to be exact:

If you're looking for an approachable guide that teaches you how to implement an easily-customizable service layer in PHP, then take a peek at this article series. In a step-by-step fashion, it walks you through the development of a sample web application, which uses a service to perform CRUD operations on a domain model composed of a few user entities.

Service layer types covered in the series are:

• Working with database entities
  
• Data Mappers
  
• Database adapters
  
• Handling Entity Collections
  
• User Services
  
• Dependency Injections
  
• Modeling Domain Objects