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SOAP Vs. REST - What's the Difference?

SOAP Vs. REST - What's the Difference?

SOAP is a protocol using XML for structured web service communication, while REST is an architectural style for flexible web services via standard HTTP methods and formats like JSON. In this blog post, we’ll discuss the differences between SOAP and REST and decide when to use each of them.

Table of Contents

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What is SOAP?

SOAP is a set of rules that systems follow when they transfer structured information over the internet. SOAP also provides a standardized way to structure and format messages using XML. This makes sure that both the sender and receiver, even if they use different technologies, can easily understand and work with the information.

Real-Life Example:

Let’s understand how SOAP works with a real-life example. In below example, the SOAP request asks for book details with the book ID 123, and the SOAP response returns information about the book.

SOAP Request:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="http://www.example.com/webservice">
    <!-- SOAP Envelope: Defines the XML document as a SOAP message -->
    <soapenv:Header/>
    <!-- SOAP Header: Typically used for authentication or additional information (empty in this case) -->
    <soapenv:Body>
        <!-- SOAP Body: Contains the main content of the SOAP message -->
        <web:GetBookDetails>
       <!-- Custom Operation: Indicates the specific operation being requested -->
            <web:BookId>123</web:BookId>
            <!-- BookId Element: Parameter for the GetBookDetails operation -->
        </web:GetBookDetails>
    </soapenv:Body>
</soapenv:Envelope>

Explanation of each section:

  • <soapenv:Envelope>: The root element that defines the XML document as a SOAP message. It has two namespaces:
    • xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/": Specifies the SOAP envelope namespace.
    • xmlns:web="http://www.example.com/webservice": Defines a custom namespace for elements within the SOAP body.
  • <soapenv:Header>: The SOAP header, which is empty in this example. Headers are optional and can be used for additional information like authentication details.
  • <soapenv:Body>: The SOAP body contains the main content of the message, including the specific operation being requested.
  • <web:GetBookDetails>: This element represents the custom operation GetBookDetails within the web namespace. It indicates the type of action or service being invoked.
  • <web:BookId>: A parameter element within the GetBookDetails operation. In this example, the book ID is set to 123.

SOAP Response:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="http://www.example.com/webservice">
    <!-- SOAP Envelope: Defines the XML document as a SOAP message -->
    <soapenv:Header/>
    <!-- SOAP Header: Typically used for authentication or additional information (empty in this case) -->
    <soapenv:Body>
        <!-- SOAP Body: Contains the main content of the SOAP message -->
        <web:GetBookDetailsResponse>
            <!-- Custom Operation Response: Indicates the response for the GetBookDetails operation -->
            <web:Book>
                <!-- Book Element: Contains details about the book -->
                <web:Title>Java Book</web:Title>
                <!-- Title Element: Contains the title of the book -->
                <web:Author>Intellipaat</web:Author>
                <!-- Author Element: Contains the author of the book -->
                <web:ISBN>123456789</web:ISBN>
                <!-- ISBN Element: Contains the ISBN of the book -->
            </web:Book>
        </web:GetBookDetailsResponse>
    </soapenv:Body>
</soapenv:Envelope>

Explanation of each section:

  • <soapenv:Envelope>: The root element that defines the XML document as a SOAP message. It has two namespaces:
    • xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/": Specifies the SOAP envelope namespace.
    • xmlns:web="http://www.example.com/webservice": Defines a custom namespace for elements within the SOAP body.
  • <soapenv:Header>: The SOAP header, which is empty in this example. Headers are optional and can be used for additional information like authentication details.
  • <soapenv:Body>: The SOAP body contains the main content of the message, including the specific operation response.
  • <web:GetBookDetailsResponse>: This element represents the custom operation response GetBookDetailsResponse within the web namespace. It indicates the response for the GetBookDetails operation.
  • <web:Book>: The Book element contains details about the book, and its child elements hold specific information like title, author, and ISBN.
  • <web:Title>, <web:Author>, <web:ISBN>: These elements contain specific information about the book, such as title, author, and ISBN.

Next, let’s understand what REST is.

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What is REST?

REST stands for Representational State Transfer, which is an architectural style designed for applications to communicate and interact over the network. It is not a protocol like SOAP, rather, it’s a set of principles or constraints that guide how web services should be created. RESTful APIs (Application Programming Interfaces) are based on REST principles. 

Instead of using XML to make requests, REST usually depends on a simple URL. The REST service performs tasks using the normal HTTPS verbs (GET, POST, PUT, and DELETE).

Real-Life Example:

In the below REST example, a simple HTTP GET request to the /api/books/123 endpoint returns a JSON representation of the book details.

REST Request:

GET /api/books/123

Explanation:

  • GET: This is the HTTP method used to retrieve information from the specified resource. In this case, it indicates a request to retrieve book details.
  • /api/books/123: This is the resource URI (Uniform Resource Identifier) that specifies the location of the resource on the server. In this example, it indicates the resource for retrieving details about the book with the ID 123.

REST Response:

{
"title": "Java Book",
"author": "Intellipaat",
"isbn": "123456789"
}

Explanation:

  • "title", "author", "isbn": These are the keys in the JSON object representing different attributes of the book.
  • "Java Book", "Intellipaat", "123456789": These are the corresponding values for the attributes, providing specific information about the book.

Many developers found SOAP difficult to use. That’s where REST came in, offering a more lightweight alternative.

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What is the Difference Between SOAP and REST?

What is the Difference Between SOAP and REST?

Here are the main differences between SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) worth considering:

ParameterSOAPREST
Full formSOAP stands for Simple Object Access ProtocolREST stands for Representational State Transfer
ProtocolXML-based, RPC-style (remote procedure call)HTTP verbs based, JSON/XML, etc
Message FormatEnvelope structure, custom XML tagsStandard HTTP verbs (GET, POST, PUT, DELETE) and JSON/XML payload
State ManagementSession-based, requires SOAP headersStateless, relies on resource URIs
ComplexityMore complex to design and implement due to complex integrationsMore flexible and lightweight for modern APIs and microservices
IntegrationDesigned for enterprise application integration (EAI) and cross-platform communicationMore suited for modern, distributed architectures and APIs
Use CasesEnterprise data exchange, B2B integration, secure transactionsPublic APIs, mobile apps, microservices, web applications
ScalabilityScaling SOAP is challenging because the server keeps track of the ongoing conversation with a client by storing all past messages.Scaling REST is easy. It’s stateless, meaning each message is handled independently of previous ones.
Developer ExperienceRequires specialized tools and knowledge of XML and web servicesLeverages common web technologies and tools, making it easier for developers to pick up
PerformanceSOAP is not as fast and lighter than RESTREST is often considered faster and lighter-weight

Choosing the Right Approach for Their Web

In the above part, we have seen a tabular comparison of SOAP vs REST APIs, but they differ significantly in terms of design, flexibility, performance, scalability, security, and reliability. Understanding these differences is important for developers and architects when choosing the right approach for their web services. Here are the following:

ParameterSOAPREST
DesignUses a strict and standardized protocol, often XML-based, with a predefined structure.Lightweight design, commonly using JSON format, allowing for simpler and adaptable structures.
FlexibilityRigid, only allows XML messaging. Maintains the state of each client, remembering previous requests.More flexible and supports data transfer in various formats (plain text, HTML, XML, and JSON). Stateless treats each request independently
PerformanceLarger, more complex messages lead to slower transmission and processing, impacting page load times.Faster and more efficient due to smaller message sizes. Responses are cacheable, enhancing performance.
ScalabilityXML’s complexity and lengthy messages can create processing delays, impacting how well the system can scale, or handle increased demands and growth efficiently.REST’s simplicity and lightweight messages make processing faster, improving scalability by efficiently handling increased demands and allowing the system to scale effectively.
SecuritySOAP provides built-in security features, such as WS-Security, which includes mechanisms for authentication, authorization, integrity, and confidentiality.In REST, security is achieved through HTTPS, which encrypts data during transmission.
ReliabilityBuilt-in error handling and offers more reliability.Less reliable and requires retrying in case of communication failures.

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When to Use SOAP Vs. REST

When to Use SOAP vs REST

Use SOAP when:

  • Strict Standards: In industries like finance or healthcare, where adherence to strict standards is crucial.
  • Built-in Security: Applications requiring comprehensive security features provided by protocols like WS-Security.
    Example: Online banking systems, where standardized communication and robust security are essential.

Use REST when:

  • Flexibility Matters: For mobile apps or web applications where flexibility in data formats and lightweight communication is key.
  • Scalability Needed: When handling a large number of simultaneous requests or building scalable systems.
    Example: Social media platforms, where quick and adaptable communication is essential for diverse clients.

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Conclusion

SOAP Vs. REST API – which one is the right fit for your API design needs? The answer is  ‘Depends’. Each protocol has its advantages and disadvantages. SOAP’s rigid protocol structure and lower-level focus prevent it from fully aligning with REST’s architectural principles. On the other hand, REST’s flexibility and higher-level abstraction enable it to leverage various protocols, including SOAP, when appropriate. Ultimately, the choice between SOAP and REST hinges on the specific requirements of your project, with SOAP aligning well with complex, transaction-heavy applications and REST catering to lightweight, scalable services.

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About the Author

Senior Consultant Analytics & Data Science

Presenting Sahil Mattoo, a Senior Consultant Analytics & Data Science at Eli Lilly and Company is an accomplished professional with 14 years of experience across data science, analytics, and technical leadership domains, demonstrates a remarkable ability to drive business insights. Sahil holds a Post Graduate Program in Business Analytics and Business Intelligence from Great Lakes Institute of Management.