What Is SOAP (Simple Object Access Protocol)?

It's the reason websites work so easily

By
S.E. Slack
S.E. Slack
Writer, Editor
S.E. Slack has 30+ years' experience writing about technology. She has authored 12 books and thousands of articles, and she has worked for IBM and Microsoft.
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S.E. Slack
Updated January 08, 2020

SOAP (Simple Object Access Protocol) is an internet protocol that allows programs within different operating systems or on separate servers to talk to one another over the internet. SOAP typically uses XML and HTTP protocols in its processes, but it can also use SMTP as well.

Illustration of SOAP working with other protocols
 exdez/DigitalVision Vectors

Why Was SOAP Created?

Software providers such as Microsoft, IBM, Lotus and others came together to solve a problem common between them: Online programs that couldn't be used properly when shared between different operating systems and servers. Because the programs didn't share the same language, it created problems for people when they attempted to use different parts of websites.

The industry solution for that problem was SOAP, an XML-based internet protocol that lets applications or objects within an application speak to one another. All of this involves the back-end, or the complicated computer programming details that you never see when you use a website.

Think of it this way: SOAP is just a way to combine XML, HTTP and/or SMTP programming languages to send and receive messages over the internet. It is not constrained by the application language (Java, C#, Perl) or the platform (Windows, UNIX, Mac), and this makes it much more versatile than other solutions.

How Does SOAP Work?

Here is an example of a common problem and how SOAP resolved it.

You use online banking to access your bank accounts. Your bank offers the following options:

  • Online banking (account reviews, transfers, stop payment, etc.)
  • Online bill paying
  • Online credit card management

Even though the bank offers those three options on a single website you can see and access, they're still completely separate applications running on different servers and, often, use completely different programming languages or even operating systems behind the scenes.

Without some way for each one to talk to another, you can't transfer funds from your savings to your credit card, for example, or view your checking account balance from the online bill pay section of the site.

That's where SOAP comes in. Without you ever realizing it's involved, SOAP quietly combines all those different languages into a single, simple interface that you see and use seamlessly. You simply perform the actions you want and SOAP makes everything work properly. The end result is an online experience that is simple and fast to use.

Is Simple Object Access Protocol Still Needed?

SOAP is still widely used around the world. As the internet grows and technology changes, however, more and more developers are turning to a lighter-weight solution called REST (Representational State Transfer).

There are significant differences between the two that matter to developers but most people will never know which one is running the online services and websites they use. SOAP is still widely used and it will be a very long time, if ever, before it is fully replaced by any other internet protocol.