For the final part of this chapter, we're going to show you how your application can interact with these transaction functions in business networks using APIs. The sample application and the Playground both interact with the business network using APIs.
Indeed, you can see that from a service consumer's perspective, neither Alice, Bob, Matias, nor Ella were aware of the blockchain–they just interacted with some user interfaces that resulted in these transaction functions (or similar) being executed to manipulate the business network according to the business logic encoded in these transaction processing functions.

It's these user interfaces and applications that use APIs to interact with the business network. If you're new to APIs, then you can read about them here. Although more technically accurate, few people use the term Web API–it's just API:

Let's have a look at the APIs for our business network! If you select the final tab in the demo, you'll see the following page:

This is the Hyperledger Composer REST server. It is a server that's exposing the APIs in our business network. These APIs are described using a standard SWAGGER format.