SOAP vs REST: Protocol Comparison

This article compares SOAP and REST protocols, outlining the key differences between them. Let’s delve into the basics of each.

SOAP Protocol

• SOAP stands for Simple Object Access Protocol.
• It uses XML messaging to exchange information between computers over the internet.
• SOAP can extend HTTP for XML messaging.
• It provides data transport for web services, capable of exchanging complete documents or calling remote procedures.
• It can be used to broadcast messages.
• SOAP is platform and language independent.
• SOAP is not tied to any particular transport protocol. Therefore, SOAP messages can be transported via SMTP, HTTP, FTP, MQSeries, or MSMQ. HTTP is the most common transport protocol for SOAP.

Figure 1 depicts SOAP protocol messages between sender and receiver.

• A SOAP message contains the following elements: envelope, header, body, and fault.
  • Envelope: Defines the start and end of the message. This is a mandatory element.
  • Header: Contains optional attributes of the message used in processing, either at an intermediate or endpoint. This element is optional.
  • Body: Contains the XML data that comprises the message being sent. This is a mandatory element.
  • Fault: Provides information about errors that occur while processing the message. This is an optional element.
• SOAP Encoding: Includes a built-in set of rules for encoding data types. SOAP data types are divided into scalar and compound categories.
  • Scalar types contain exactly one value, such as a last name, price, or product description.
  • Compound types contain multiple values, such as a purchase order or stock quote list. Compound types are subdivided into arrays and structs.
  • Scalar types include strings, floats, doubles, integers, date, time, boolean, decimal, binary, long, short, byte, etc.

REST Protocol

Figure 2 depicts the REST protocol stack.

REST stands for Representational State Transfer. As shown in the image, it’s built on HTTP/TCP layers.

The REST protocol uses a bus-based architecture where no broker component is needed, and end devices can communicate directly. Request and response messages are used between end devices to exchange information.

Difference between SOAP and REST

The following table highlights the key differences between SOAP and REST protocols:

Conclusion

From the comparison above, we can conclude that SOAP is a protocol, and REST is an architectural style. A REST API can utilize the SOAP protocol, similar to its use of the HTTP protocol.