H2A - Human to Application Services
Human 2 Application Services is an implementation of a use-case/user story
Implements one, and only one human actor
A2A - Application to Application Services
Orchestrates services from several applications, typically asynchronous and workflow-backed.
ACS - Aggregated Core Services
ACS is usually either context-specializing (CustomerCustomer and VendorCustomer) or aggregations from several Core Services like in a CustomerDashboard.
CS - Core Services (Domain/Resources)
Core Services is basically data services. Typically they evolve to become the master repository for the most important business objects in the enterprise.
Typical examples are Customer and Product.
This updated version incorporates extensive feedback from users and experience in deploying the original categorization model in projects, and tighten a few key specializations we experienced we need to make sure that everyone in an organization understand both the model and where to place all their services in the service universe.