One of the common questions we get from product folks is what the difference is between rest and soap in layman's terms. There are a whole host of technologies that support the online services that we use every day. Web APIs are an integral part of the online ecosystem. The API or application programming interface can be for a web browser or a web server. When developers write code for the web, they need to choose the Web API that suits the requirements of their project.

There are several different types of Web APIs. They allow two applications to interact with each other through a set of rules. Developers can use these APIs to add specific functionality to their apps without having to write all of the code from scratch.

Soap and Rest are among the most popular Web APIs. They're widely used by developers for their convenience and functionality. Each has its own advantages and disadvantages.

What is Rest?

Representational state transfer or Rest was developed to work with components like media, files or objects on a hardware device. Roy Fielding introduced and defined this term in his doctoral dissertation back in 2000. The idea was to detail how a well-designed web application would behave. Web services that are defined on the principles of Rest and therefore called RestFul web services.

A resource is the key abstraction of information in Rest. Any information that can be given a name can function as a resource. It can be a collection of other resources, a document, an image, etc.

It uses a resource identifier to identify the particular resource that's required in an interaction between components. When HTTP is used in a transition, as it most commonly is, the GET, HEAD, POST, PUT, PATCH, DELETE, CONNECT, OPTIONS and TRACE operations are available. This typical use of HTTP means that developers don't need to install any extra software or libraries when they create a Rest API.

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Advantages

  1. Greater flexibility

    This is perhaps one of the biggest advantages of a Rest API. The greater data flexibility is made possible because data is not tied to any resources or methods. Rest is thus able to work with different types of calls and return different data formats. It can even change structurally with accurate implementation of hypermedia.
  2. Better scalability

    Many developers also choose to utilize the Rest API because of its scalability potential. This is made possible by the separation between the client and server. Rest operates on the concept that the client and server should be separate so that they can evolve on their own. This allows the development team to scale the product with relative ease.
  3. Rest APIs are stateless

    Their stateless nature makes Rest APIs unique. Stateless in this respect means that none of the previous requests or responses are saved by the server. Every message is isolated so it's necessary for all of the data to be sent with the request. This makes every request more understandable and purposeful.
  4. Uniform Interface

    This is another big advantage of the Rest API. Developers use the same standards and that means every API has the same uniform interface. The Rest API from one application can thus communicate in exactly the same manner with a completely different application, allowing for more efficient communication.

Disadvantages

  1. Bound by constraints

    Rest APIs are by and large bound by six architectural constraints which include the uniform interface, the client-server based nature, stateless operations, layered system architecture, etc. It’s important to understand that these constraints exist before building out your API.
  2. Learning curve for new developers

    It’s not exactly beginner friendly. Developers who aren't highly skilled might find themselves going through a steep learning curve when developing a Rest API. If they don't understand the limits of this web technology they could end up in situations where they get frustrated with its limitations.
  3. Lacks security

    Unlike other Web APIs, Rest doesn't impose any security protocols. This means that it's not the ideal technology if the service requires confidential data to be passed between the client and server. On the other hand, it's better suited to publicly available services.
  4. Limited transfer protocol support

    Other Web APIs like SOAP have support for a variety of different transfer protocols, including but not limited to HTTP, SMTP, UDP, and more. This puts Rest at a disadvantage since it only has support for the HTTP transfer protocol.
Soap Request

What is Soap?

SOAP or the Simple Object Access Protocol is a messaging protocol that allows for distributed elements of an application to communicate. This protocol can be carried over multiple transfer methods like HTTP and SMTP. Its data structure is based on XML and since it's largely human readable, it makes it easier to understand a SOAP message.

SOAP is a concrete protocol with its own set of rules and security features like integrated ACID compliance and authorization. It's also highly complex since it requires more bandwidth and resources. It performs well in distributed enterprise environments since it doesn't assume direct point-to-point communication.

Advantages

  1. Highly secure

    SOAP APIs are used for enterprise-level web services that require enhanced security. Some of the most common APIs that use SOAP include those for payment gateways, financial services, CRM software, and more.
  2. Legacy system support

    SOAP is also highly preferred because of its support for legacy systems. Services that have been around for a while might have users that continue to utilize their services through the API. This ensures that users with legacy systems can continue to have access.
  3. Supports stateful operations

    SOAP APIs are stateless by default but the great thing about SOAP is that it has support for stateful operations as well. This can be implemented with Web Services Specifications built on top of the XML standards. It's useful for scenarios where a chain of operations has to be made, such as bank transfers.
  4. Built-in error handling

    Built-in error handling is a big advantage because if there's a problem with a request, the response will have the error information that can be used to fix the problem. This eliminates the guesswork from finding out exactly what went wrong.

Disadvantages

  1. Highly complex

    In comparison to Rest, SOAP is significantly more complex. It's also less flexible. This might present a challenge for developers that are not highly skilled. The extensive processing required may also slow down performance.
  2. No variety of data formats

    SOAP is also extremely limited in its support of data formats. The formats supported by Rest include HTML, JSON, YAML, XML and others. Meanwhile, SOAP only supports XML.
  3. API calls are not cached

    The process where a request is sent after an API is set up with the correct endpoints is referred to as an API call. The process results in the information being transferred, processed and feedback being provided. It's not possible for SOAP API calls to be cached.
  4. Uses more bandwidth

    SOAP is generally slower in comparison to Rest and it also uses more bandwidth given its very complex nature. It’s another limiting factor in the efficacy of this technology for certain projects.
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Which is better?

Most experts have reached a consensus that Rest should be the preferred platform unless there's a good enough reason to use SOAP instead. However, it can't be ignored that there are very specific use cases in which SOAP would be the obvious choice.

SOAP is an excellent solution for situations where Res can't be used, particularly if stateful operations need to be processed. A SOAP API makes it possible to have a chain of operations in a single transaction. Something that’s not going to be possible with a Rest API.

Those looking to build out enterprise-level web services will naturally prefer SOAP owing to its advanced security measures. PayPal's public API is one of the prime examples of a SOAP API.

This API enables PayPal users to accept payments through PayPal and credit cards, add a PayPal button to their own websites and ecommerce stores, in addition to logging in with PayPal.

These days, most developers that build public APIs opt for Rest given the increasing popularity of this technology. All of the big social media services provide Rest APIs, allowing developers to easily integrate their apps with the platform.

Twitter's public API is one such example. It serves a variety of purposes like enabling users to find historical tweets, an ad API for managing advertisements and a Direct Message API to send personal messages to users.

SOAP and Rest have their strengths and weaknesses. Just how better one is compared to the other largely depends on an organization's needs. They will need to pick the API that makes the most sense for their specific use case. Generally, organizations that need to offer public APIs are going to use Rest because of the advantages that have been discussed in this post.

Rest is also preferred for most new APIs because the development work is relatively simple and it also consumes less bandwidth. It's easier to understand for developers which makes the initial implementation of APIs fairly simple. Those that need confidential data to be transferred over the API will prefer SOAP given its enhanced security.