Simple Object Access Protocol (SOAP) is a message specification for exchanging information between systems and applications. When it comes to application programming interfaces (APIs), a SOAP API is developed in a more structured and formalized way. Think of SOAP as being like the national postal service: It provides a reliable and trusted way to send and receive messages between systems (and within enterprise applications). It is older, established, and dependable—but it can be slower than competing architectural styles like REST.
How SOAP API works
SOAP allows you to receive responses from a variety of XML document platforms. XML documents include coding consisting of the following tags:
- Message: The message is the information shared between two applications. When one application sends a request to another, the second software authenticates the first with an API key to grant it access to information. For example, when your analytics dashboard pulls data from Google Analytics, the software must ensure that there’s a Google Analytics API key that allows them to communicate.
- Header: The header element provides additional information for the message being sent.
- Envelope: The SOAP envelope is the core element of a message and includes the XML document message.
- Body: The body of the soap message includes the request or response from one program to another.
- Fault: The fault tag displays data about errors throughout the process.
Benefits of using SOAP
While every organization prefers REST API or SOAP API, some benefits of using SOAP include:
- Standard protocols: With SOAP’s standard HTTP protocol, it’s easier to operate across proxies and firewalls without having to make any modifications.
- Enhanced security: SOAP offers robust security with the assurance of data privacy and integrity while supporting identity verification through third-party encryptions such as SSL.
- Reliable transactions: With the use of HTTP, SOAP allows for greater transaction reliability. This helps with ACID-compliant transactions in the event of errors, power failures or other mishaps.
- Neutral functionality: SOAP APIs can operate over various communication protocols, including simple mail transfer protocol (SMTP), transmission control protocol (TCP) and HTTP.
- Less coding: When dealing with complex operations, SOAP requires minimal coding in the application layer for security, transactions and other elements. This can make it relatively easy to learn how to work with SOAP.
- Greater extensibility: SOAP is extensible through other technologies and protocols. SOAP supports various web services, including WS-Security, WS-Coordination, WS-Reliable Messaging and WS-Addressing.
- Independent operation: Because of its independent operation and compatibility with any programming language, SOAP API is convenient for various organizations and web developers.
SOAP API disadvantages
While SOAP can be extremely useful in certain situations, there are also times where REST may be the better option. Some drawbacks include:
- SOAP does not support caching API calls.
- SOAP is much more complicated than REST, which can have performance implications.
- SOAP is much less adaptable than REST.
SOAP is usually slower than REST.