service oriented architecture vs headless architecture

I have a question about service-oriented architecture and headless architecture. Are they the same concept, or can headless architecture be considered a subset of service-oriented architecture?

They are completely different architectural styles that address totally different problems.

Service Orientated Architecture (SOA)

An architectural style that applies to (up to) enterprise-wide (inter-system / inter-solution) service architecture.

SOA features completely independent services where the intent of a service ties back strongly to business (organizational) units and their business functions.

• May use a central service repository / directory.
• May use of a central service/event broker, service bus.
• Services are likely to be stateful.
• Historically implemented using SOAP and webservices.
• Tends to be message-based (as opposed to event-based) where there can be a contract between the services (or at least an implied one).

Above is an example "toy" SOA architecture, but please note that there are different variations of how you might implement a solution based on the SOA style - this example illustrates the style at a high level.

Headless Architecture

An architectural style that applies to application architecture and development.

In headless you would essentially create an application that had everything except a user interface (UI); instead of providing a UI the application would provide an API designed to service a UI.

You might use this style if you wanted to have two independent teams, one focusing on the backend, the other on the UI; but there are other reasons why you might choose this approach.

If you are interested in headless you may find the "Backend for Frontend" pattern useful.

Lastly - the key idea of Headless Architecture is simply to separate the frontend from the backend - you can still architect the backend any way you like e.g. Clean, Hexagonal / Ports & Adaptors, MACH, etc.

Any number of UI's can consume the same "headless" backend. It is assumed that the UI's are located on tiers that are different from the headless backend - this is not required but is typically what happens in practice. The UI's can be made from completely different technologies and hosted in different locations (hence Presentation tiers).