The Application Architecture describe the software applications that support the business processes and business capabilities by providing application services.
Application Architecture Building Blocks
At the highest level of IT planning and in a future state Application Architecture model, the applications are represented as Building Blocks.
These are candidate application components that will subsequently be realised by real COTS applications or the development of new bespoke applications.
TOGAF has a good discussion of Building Blocks.
Another useful resource is the FEA Service Component Reference Model.
This describes Application Components from a Service perspective linked to the other FEA reference models.
A good starting point to understanding the FEA Reference Models is to read the FEA Consolidated Reference Model document
Application Domains and Application Services
The applications, application data and interfaces are strongly aligned with the future state model of business processes, business information and event value chains (workflows).
The approach is inspired by Service Oriented Architecture (SOA) in order to allow for modular design, maintenance and timely renewal of application components.
At the highest-level there is a very strong focus on application building blocks and application services, as opposed to the old view of simply thinking in terms of applications and databases.
The Application Domains are the high level packages that group Applications and Application Services.
An Application Domain is based on an Application Layer or related to a Business Process, Business Function or Business Capability.
Service Oriented Architecture
EA is about realizing the business strategy and developing a future state enterprise architecture model together with a roadmap of strategic business and IT initiatives to achieve the vision and target operating model.
Introducing the concepts of a business service and an application service to the business areas is typically one of the first of those initiatives.
Once the business understand the value of thinking in terms of services, then the EA roadmap can introduce Service Oriented Architecture (SOA) as a technology enabler to deliver services in practice.
This can be a long journey and without EA, Service Oriented Architecture (SOA) will be seen as a bottom up techie fad rather than something of value.
I’ve seen several successful SOA pilots that didn’t lead to the widespread use of SOA simply because it wasn’t grounded in the Strategy and Enterprise Architecture first.
ArchiMate Information Layer Meta Model