As always, the cause of this misnomer can be found in history. Deploying software used to be a complex thing in the past as was software development and even more so developing software that communicates with other software. A ton of different concepts, protocols and technologies have emerged over time to facilitate the connectivity between different pieces of software. (Skip the next section when you're not interested in a short but incomplete overview of software interoperability)
here and I'll write a little update on the topic soon as many ESB aficionado's don't see this yet.
So after we started omitting ESB's from our IT landscapes but kept the ESB concept around, we finally found ourselves in a world that actually delivered on promises and was low cost; The Internet.
Web-servicesYou can skip this part if you already know everything about web-services and are not interested in what I have to say about them. It's relevant, but not such that you can't skip over this section.
So web-services, both SOAP and REST-based, are interesting little beasts in our IT landscape. Web-services are the first real useful concept when realising an SOA. A Service Oriented Architecture. Based on Internet technology and therefore implicitly complying with all the requirements of an SOA.
And then there's the fact that web-services are accessed through a simple interface, the URL. So even in case you don't think about it, you're forced to limit the scope of what a web-service can do because you're limited to a URL. And although behind many URL's there can be a single monolithic structure, or you can use all kinds of different ways of encoding many functions within one URL, there really is no point in doing so, because working with URL's makes it harder to do things the wrong way than to do it the right way.
And the cool part is that this is true for even high level business functions that require a variety of (technical) low level web-services. On every level, working with web-services (almost) requires you to develop software that do only a single (business) function. As such, a web-service can be considered an application.
Web-services make it harder to do it wrong than to do it right.
If you look at it this way, a web-service being an application, you can see that a web-service is a small piece of software that provides just enough functionality for another piece of software or a person, to consider useful.
In effect; Every web-service, by means of its interface exposed as a URL, is exposing a (business) function. And as soon as you aggregate various web-services into a new web-service, meaning you call several web-services in a particular order to implement a high level business function, your new web-service complies to the same rules.
When we look at API's, they're the interface that we put in front of some software to expose specific business functionality. Look at the previous post on the topic by clicking here.
API's are products. There's an intended full stop because in many ways people tend not to think that way. But really, an API is where the boundary of a system is. The rest of the world accesses that software system through the API. The rest of the world might be a user interface.
So if you think about API's being products, or possibly a set of API's being a product, you're on the right track, because you then understand that a web-service is not a product in itself, instead it is a piece in a product's puzzle.
Why this is important? Because the API developer has the responsibility towards the consumers of the API, ensuring that changes to the API do not impact existing consumers of the API and lure new consumers at the same time. A developer of a web-service does not have this responsibility. or rather there's a way out.
Remember that in a previous post I mentioned that an API does not make any assumptions about it's consumers. They're not known in advance and any assumed consumer is likely not the biggest fan. Web-services on the other hand do know their consumers. Or at least, they can be developed such that assumptions are made regarding the consumer. This is also the reason why there's a need for API management in some cases and no need at all in other cases.
The complete series:
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