SOAP vs REST API: Head to Head Comparison

October 28, 2021

Introduction

When deciding on the appropriate API for your use case, you will likely compare SOAP and REST. These two solutions are the most commonly used APIs (application programming interfaces) in web development today.

Read on to find out how SOAP and REST differ, why they are not directly comparable, and when to use one over the other.

SOAP vs API comparison.

SOAP vs. REST Web Services: Definitions

SOAP API is an XML-based messaging protocol that allows web services to communicate and exchange structured information over HTTP. Since it uses XML for writing messages, the protocol is platform and language independent and used across all operations.

REST API is an application programming interface, widely known as REST API web service (or RESTful API). The interface provides interaction with services by transferring a representation of the required resource's state over the HTTP protocol. The APIs are based on URLs (or other types of URIs) and usually use the JSON data format.

SOAP vs REST API described.

SOAP

SOAP stands for Simple Object Access Protocol. It was designed for providing access to web services well before REST. The protocol introduced a simple way for exchanging data and establishing communication between applications (even if they are built on different platforms or with different languages).

Some of the main features of SOAP are:

  • It is based on XML.
  • It is platform-independent.
  • It imposes built-in rules and compliances.

SOAP messages represent requests for data sent to SOAP APIs over an application layer protocol (such as HTTP). After each request is processed, the server returns the required data in an XML document.

Messages are encoded as XML documents and consist of the following elements:

  • The SOAP Envelope - <Envelope> is the root element that identifies the document as a SOAP message. It consist of the child elements - the <Header> (optional) and the <Body> (mandatory).
  • The SOAP Header - <Header> is an optional child element of the envelope used to pass header (application-related) information to add new features and functionalities. An envelope can have multiple headers.
  • The SOAP Body - <Body> is a mandatory child element of the envelope that contains the information you want to exchange with the recipient.
  • The SOAP Fault - <Fault> is an optional sub-element of the SOAP body used for reporting errors and status information if a problem occurs during processing. A message can only have one fault component.
SOAP API message request components.

REST

Unlike SOAP, REST is not a protocol but a set of regulations that are implemented in many different ways. REST stands for Representational State Transfer and refers to a set of architectural principles for building applications and services. A RESTful web service is a web service built on these principles.

Certain principles need to be followed for a web service to be considered RESTful. They inlcude:

  • Code on demand. Servers can send executable code to the client if needed.
  • A layered system. Architecture is composed of multiple layers of servers with different functionalities.
  • Stateless. All client-server communication is stateless - requests are not connected, and client information is not stored between requests.
  • Caching. All resources should be cacheable to streamline interactions.
  • Uniform UI. There should be a uniform interface that identifies resources, their manipulation through representation, self-descriptive messages, and hypermedia as the engine of the application state.
  • Client-server architecture. Clients and servers are loosely coupled and independent of each other. The client is concerned with the user interface and state, while the server administers data storage, access, management, and security.

To obtain resources, a client sends a request to the server. There are four basic types of commands a client can use:

  • GET - for retrieving resource representation.
  • POST - for creating a resource.
  • PUT - for editing an existing resource.
  • DELETE - for deleting an existing resource.

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SOAP vs. REST Web Services: Quick Comparison

Now that you understand the basics of SOAP and REST APIs, take a look at a head-to-head comparison on how they differ by specific criteria.

SOAPREST
DESIGNstandardized protocolarchitectural style
APPROACHfunction-drivendata-driven
STATEFULNESSstateful or statelessstateless
CACHINGAPI calls are not cachedAPI calls are cashed
RESOURCESmore bandwidth, extra overheadless bandwidth, lightweight
SECURITYWS-security, SSL, built0inHTTPS, SSL
MESSAGING FORMATXMLJSON, HTML, XML, YAML, plain text, etc.

Protocol vs. Architectural Style

The main difference between SOAP and REST is their design. SOAP is a standardized protocol with pre-defined rules.

REST is an architectural style with recommendations, constraints, and loose guidelines.

Data as a Service vs. Data as a Resource

SOAP is function-driven. APIs perform operations, and the data is available as a service. REST is usually data-driven. Data is available as a resource that is accessed through APIs.

Stateful vs. Stateless

By default, SOAP is stateless but can be made stateful with a simple code change.

REST is completely stateless, and there are no server-side sessions.

No Cache vs. Cache

Caching is a time and resource-efficient feature that allows a browser to reuse data without sending a new request to the server. SOAP API calls cannot be caches, while REST API calls are cacheable.

Resource Heavy vs. Lightweight

There is a significant difference in resource requirements when it comes to SOAP vs. REST. Due to its envelope-style payload transport, SOAP requires more resources to start with. Additionally, it also needs more bandwidth to transmit its data-heavy requests.

REST is a lightweight solution that requires less resources and bandwidth.

More Secure vs. Less Secure

SOAP has WS-security, SSL support, and built-in ACID compliance. Therefore, it is appropriate for exchanging sensitive information and ensuring enterprise-level security.

REST supports HTTPS and SSL and is commonly used for publicly available URLs. It provides communication encryption with TLS but should not handle sensitive information without additional security implementations at the server level.

Single Messaging Format vs. Various Messaging Format

SOAP APIs support an XML-based messaging protocol only. SOAP clients often need third-party libraries for communicating with APIs.

REST APIs tend to use JSON and support various other formats, including HTML, XML, YAML, plain text, and others.. REST clients only need the HTTP request libraries built into the programming language.

SOAP Advantages and Disadvantages

Advantages

  • Language, platform, and transport independent.
  • Standardized, secure, and enterprise-friendly.
  • Built-in error handling and pre-built extensibility with WS-standards.
  • Supports automation when used with specific languages.

Disadvantages

  • Less performative due to XML document size and more bandwidth requirement.
  • Tightly coupled applications where the client-server communication depends on WSDL contracts.
  • More complex to set up and test compared to REST.

REST Advantages and Disadvantages

Advantages

  • Simple to understand and learn, easier to code.
  • Requires less resources and bandwidth.
  • No routing information is needed to access data thanks to URIs.
  • Faster performance due to its caching feature.
  • Autonomous development across different sections of a project due to separation between client and server.

Disadvantages

  • Less secure and not suitable for working with confidential data.
  • Its statelessness requires the clients to manage state if needed.
  • Not capable of obtaining multiple data pieces in a single request.

When to Choose SOAP?

For operations that need to be highly controlled and described in detail, SOAP offers failproof stability. Its pre-defined standards and constraints ensure greater security compared to REST. Additionally, SOAP provides the WS-structure that supports stateful operations. Therefore, it is a better choice when maintaining state is important.

When to Choose REST?

Choose REST over SOAP in cases where you have limited bandwidth and resources. Also, if maintaining a state of information isn't a priority in your use case, opt for the stateless REST API. Finally, this solution is the way to go in scenarios where caching and ease of coding play a key role.

Conclusion

Choosing the right API solution an important step in development. Now that you understand how SOAP and REST work and how they differ, you can decide which one to use based on your use case.

Next, you might be interested in our How to Use Git article.

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Sofija Simic
Sofija Simic is an aspiring Technical Writer at phoenixNAP. Alongside her educational background in teaching and writing, she has had a lifelong passion for information technology. She is committed to unscrambling confusing IT concepts and streamlining intricate software installations.
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