In my previous posts I showed layers and components, and layers and tiers.  In this post, I'll show the services layer in a layered architecture.

Services Layer
Here's a visual example of a services layer, where the application is exposing services:

Note that services don't need to be "web" services.

Key Services Layer Components
Here's the key components of a services layer:

• Service Interfaces. The service interface acts as a facade that exposes the business logic to potential consumers.  The definition of the set of messages that must be exchanged with a service in order for the service to perform a specific business task is the contract.
• Message Types. Message Types are “message contracts” for communication between service consumers and providers.  They wrap business entity components into specific messages for the calling service.

Additional Resources

• Designing the Components of an Application or Service (App Arch Guide)
• Architecture (Web Service Software Factory: Modeling Edition)

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