Understanding SOAP vs REST: Basics And Differences

An API implies the Application Program Interface. The Application Program interface is an interface between multiple software intermediaries. The use of the Application Program Interface is seen in daily life, whenever we use Facebook, chatting applications, or wish to check the weather on mobile phones. In other words, the application program interface enables any two software applications to communicate effectively. 

The Web API is an interface for web browsers or servers. The SOAP and the REST are two different types of Web API services. These two web API services are used extensively. However, the SOAP and REST services are not the same. There are several differences between them. What is an API?

An Application Program Interface (API) enables any two or more software applications to communicate. The communication process involves a server. 

How does the API work?

Whenever a person utilizes any mobile application, it gets connected to the internet and transmits the information to the server. The server interprets the data and carries out the required operations on the receipt of the information on the server-side. After that, the server sends the data back to the mobile phone. On receipt of the data, the mobile application interprets it and presents the information to the user.  

There are web application program interfaces and web service APIs. Generally, you will see the four distinct kinds of web APIs. They are Open APIs, Partner APIs, Internal APIs, and Composite APIs. On the other hand, web service APIs are SOAP, XML-RPC, JSON-RPC, and REST. This article primarily focuses on only SOAP and REST web service APIs and the difference between them. 

Before we see the differences between the SOAP and the REST APIs, we shall know precisely what SOAP and REST mean. 

What is SOAP API Protocol?

Simple Object Access Protocol is the full form of the SOAP protocol. It is a protocol used in messaging or communication, specially developed for Microsoft. The primary objectives of the SOAP API Protocol are to offer extensibility, verbosity, independence, and neutrality. 

For message transmission, the SOAP API Protocol usually depends on the application layer protocol, called HTTP (Hypertext Transfer Protocol). Many times, it also relies on the SMTP (Simple Mail Transfer Protocol) for the communication between legacy systems. As the SOAP protocol is used for message transmission, it utilizes the XML Information Set for message formats.  

As mentioned above, the SOAP Protocol offers three significant objectives, extensibility, neutrality, and independence. The extensibility of the SOAP API implies security and WS-Addressing. Another objective neutrality means the SOAP protocol can work with any protocol, like SMTP, TCP, UDP, or HTTP. Lastly, independence refers to the idea of allowing any programming model to work with SOAP protocol.

The SOAP API Protocol relies on the XML protocol for the message transmission and has the three significant segments:

  • The first segment is an envelope. It represents the message structure and how the message should be processed. 
  • A set of encoding rules is the best part of the SOAP API Protocol. As its name suggests, it contains rules and regulations for defining data types. 
  • The last segment is a convention, which includes procedure calls and responses. 

The message in the SOAP API Protocol is represented in an XML document. It consists of four different elements, envelope, header, body, and fault. An envelope finds the XML document as a message in the SOAP Protocol. The header of the message includes header data, and the body involves procedure calls and response information. Lastly, the fault segment offers all information about the different kinds of errors occurring during message processing. 

What is the REST API?

Representational State Transfer is the full form of REST web API service. The REST web API service is not a protocol; instead, it is an architectural style. It represents all essential constraints used during the web service development process. Any web service that adapts the REST architectural style is referred to as the RESTful web service. 

There are pre-defined stateless operations in the REST API architectural style that enable requesting systems to obtain the web resources and manipulate them. The REST architectural style consists of six constraints, which avoids the server’s ways of responding to clients’ requests. Each of the six constraints is explained as follows:

soap vs rest API
  1. Uniform Interface: The uniform interface constraint implies that the client should uniformly communicate with the server, irrespective of any device type or application. 
  2. Stateless: We know that the REST architectural style uses stateless operations. The stateless constraint states that any state required to manage a client’s request is present in that particular request only. The server does not have anything about the session. 
  3. Cacheable: When the server transmits the response to a particular client’s request, it must contain the information about whether the server’s answer is cacheable or not. Additionally, it must also include information about how long the response can be cached. 
  4. Client-Server: There should be a client-server model in the REST architectural style. This architecture involves clients and servers. The client requests data, and the server holds resources. However, the client is not worried about data storage, and the server does not have to do anything with the user interface. 
  5. Layered System: The REST architectural style system should consist of several layers. A single layer in the REST system is only concerned with its immediate layer and not any other system layers. 
  6. Code on Demand: In the code on demand constraint, the server can offer an executable code to its client. Some instances of the code on demand constraints are JavaScripts, Java Applets, etc. 
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We have seen the SOAP API Protocol and REST architectural style of web API service. Let us now focus on the difference between SOAP vs REST web API services. The following section will provide detailed information about SOAP Vs. REST API services. 

SOAP vs REST Web API Services

Both Rest architectural style and SOAP protocol are very beneficial and have their own pros and cons. We shall discuss some significant and primary differences between the SOAP protocol and the RESt architectural style. 

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SOAP Web API ServiceREST Web API Service
The SOAP Web API Service is a protocol. The Representational State Transfer API is an architectural style. 
Simple Object Access Protocol is the full form of the SOAP. Representational State Transfer is the full form of REST web API service. 
SOAP cannot use the REST API, as the REST API is an architectural style. The REST architectural style can use the SOAP, as SOAP is just an underlying protocol. 
The Simple Object Access Protocol is compatible with only the XML format. Representational State Transfer is compatible with multiple formats, like plain text, XML, JSON, HTML, etc. 
The business logic in SOAP can be exposed using services interfaces. The business logic can be detected using URI (Uniform Resource Identifier)
SOAP consumes a large number of resources and bandwidth. REST consumes relatively less number of resources and bandwidth. 
This protocol is used less than the REST web API service. The REST web API service is the most commonly used. 
SOAP incorporates the Secure Socket Layer (SSL) and WS-Security. REST uses the Secure Socket layer (SSL) and HTTPS for security.  

The above table depicted clear differences between SOAP and REST web API services. But, you might feel when should we use SOAP and when should we use REST. The below points will undoubtedly clear your doubts about when to use SOAP and REST. There are specific factors that determine when you should use SOAP and when you should use REST. 

When should you use REST?

There are four specific instances where you should REST. They are explained as follows:

  1. Limited Resources and Bandwidth: The REST architectural style should be used when there are limited resources and bandwidth. On the contrary, SOAP messages are heavier than REST messages and require many resources and bandwidth. 
  2. Statelessness: You can REST architectural style when there is no requirement of storing the state of data. In other words, when the information flow of one request is not required in the other requests, REST can be used. On the other hand, the SOAP protocol is used when any particular request’s information state is used in another request. You can take an instance of online shopping sites. Whenever you desire to purchase any product from the online site, you need to add that particular product to the cart. All products in the cart are taken to the payment page for paying the calculated amount. In this instance, the state of the cart is required on the payment page. So, you can use SOAP in shopping sites for example. 
  3. Caching: When there is no requirement for caching several clients’ requests from the client. Many times, clients may need the same resources numerous times. Every time fetching resources from the server is not a feasible way. In such circumstances, implementing a cache is beneficial.  The server’s frequently accessed or used resources from the server should be stored in a cache, which acts as an intermediate location between the client and the server. When a particular client requires resources stored in the cache, it does not go to the server; instead, it accesses it from the cache.
  4. Ease of Coding: The REST services are relatively easier to code and implement than SOAP. If you require a rapid and fast response or web service solution, you can go for the REST architectural style of web API service. 

When should you use SOAP?

You have to keep in mind the three instances where you can utilize SOAP. These three instances are depicted in detail below:

  1. Asynchronous Processing: SOAP is more secure and reliable than REST. If a client requires higher reliability and security, then using SOAP is the best option. The latest version of SOAP, SOAP 1.2, provides extraordinary security characteristics. The REST architectural style uses only HTTP and HTTPS protocols. Using these two protocols may end in operation delay. On the contrary, SOAP utilizes more additional communication protocols. 
  2. Stateful Operation: We saw that REST is used when there are stateless operations. In the case of stateful operations, SOAP is used. Consider that a company requires a particular client’s data frequently to perform tasks. SOAP enables the company to preserve the earlier used client’s data. The REST architectural style does not store any information about the previous transaction. 
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Benefits of SOAP and REST web API services

Let us know the advantages of using these two web API services, SOAP and REST services. 

Pros of SOAP

  • The Simple Object Access Protocol (SOAP) is independent of language, platform, and transport. It supports multiple communication protocols. 
  • It is very well compatible with the distributed environments, i.e., it does not require point-to-point communication. On the contrary, REST only supports point-to-point communication. 
  • SOAP offers extensibility objectives using the WS-security, and it is a standardized protocol. 
  • Another advantage of using SOAP is it has built-in error handling capability and supports automation with specific languages. 

 Pros of REST

  • The REST architectural style is more manageable and straightforward to use than the SOAP API. 
  • It does not need any costly tool for communication with the web service. 
  • The REST API uses message formats that are smaller and easy to understand. On the other hand, SOAP uses the XML language set for message format. 
  • REST is faster than SOAP. It uses a more straightforward HTTP protocol for communication, whereas SOAP uses RPC or COBRA to communicate between two systems. 
  • All the four CRUD operations, create, read, delete, and update, use the HTTP protocol. 

Challenges in the SOAP Web API service

There are two significant challenges in the SOAP web API service, WSDL file and document size. The application program interface includes client and server. Browsers offer an application program interface on the client-side, whereas the web service provides API on the server-side. The web service used on the server-side can be SOAP or REST services. Let us now know the two challenges in the SOAP API in detail.

  1. WSDL File:

Web Services Description Language is the full form of WSDL. The WSDL is an XML-based language that provides information about the web service functionalities. This file includes information as follows:

  • How can the service be requested or called?
  • What parameters are required to call the service?
  • What kind of data structures does it return in response? 

The WSDL file also contains all data types of a particular SOAP message. 

Suppose there is a WSDL file having elements in it. If you desire to change a component from the WSDL file, it is very challenging. All other users who are accessing the same WSDL file have to make changes in a particular element. Hence, modifying one element by a specific user results in modifying the same component by all users accessing the same WSDL file. 

  1. Document Size:

The SOAP message is quite heavy and lengthy. So, the message size of SOAP is another significant challenge in the SOAP web API service. In many circumstances, there may be a bandwidth constraint. Therefore, transferring SOAP messages from the client to the server is one of the biggest problems. 

Challenges in the REST web API service

You can notice two significant challenges in the REST architectural style. These two challenges are lack of security and lack of state. 

  1. Lack of security:

The security in REST is less than the SOAP API. It is not suitable for the transmission of any confidential data between the client and the server. However, it is best suited for only public URLs. So, the security of REST is one of the significant issues. Using the REST API for web services is not feasible due to a lack of security. 

  1. Lack of State:

We have discussed that REST is used when there are stateless operations. Hence, a lack of state is another primary challenge in the REST web API service. We have seen an example of the shopping website, which needs a stateful operation. Products added to the cart are required on the payment page before buying them. 

Which web API service is more secure – REST or SOAP?

SOAP and REST web API services are used these days widely. The SOAP API is commonly utilized in enterprises to ensure high-end security and protect confidential data while transferring between the client and the server. SOAP and REST APIs use the same HTTP request and response protocol for exposing data, but they work differently to implement security standards. 

The SOAP API uses different patterns for ensuring message security during its transmission. These security patterns include XML-Encryption, XML-Signature, and SAML (Security Assertion Markup Language) token. On the contrary, the REST API does not use any additional security pattern. The primary goal of the REST API is to receive the data and deliver it. It is not concerned with the security of data transmission. 

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The SOAP API is more secure than the REST API. It offers high-level standardization and security. Though REST and SOAP web API services use the same HTTP protocol, the SOAP API incorporates additional WS-security. Hence, the SOAP API is highly recommended to use in enterprises. 

If you need to develop a project that involves confidential information, the SOAP API is the best web service. For example, you can use SOAP in banking, finance, etc. There is no need to use SOAP for developing mobile applications, like weather, as it does not require any private data. 

Which web API service is faster – REST or SOAP? 

The REST API is stateless. Hence, it is faster and quicker than the SOAP API. In the REST API, each verb is processed individually. REST uses the JSON object to find or traverse any field of a particular record present in the document. 

What is JSON? JSON implies JavaScript Object Notation. The significant advantage of using JSON is it is independent of language. It holds data that humans understand, like array types of data attribute-value pair data, etc. 

We know that REST processes each verb individually. But, what is a verb in REST? A verb is a specific method that is used for executing several kinds of requests. There are several verbs, like POST, PUT, DELETE, CUSTOM, PATCH. 

Remote Access Techniques

The following are some powerful remote access techniques used in REST and SOAP APIs:

  1. RPC (Remote Procedure Call):

Remote Procedure Call (RPC) is a commonly used remote access technique in REST and SOAP APIs. This remote technique is usually used in the client-server model and is referred to as a subroutine call or function call. 

When the sender or client desires to send a message request to the server, the remote procedure call transforms the request message and transmits it to the server, which is located remotely. On the message’s receipt, the server sends the response respective to the request to the client. During the server processes the request, the client is blocked. The client is unblocked only when the server finishes its task. 

One of the significant perks of using the remote procedure call is it supports thread-oriented models. The client who requests a message is not allowed to see the remote procedure call mechanism. However, the remote procedure call is not a standard technique and does not offer hardware systems flexibility. 

  1. COBRA (Common Object Request Broker Architecture):

Common Object Request Broker Architecture (COBRA) was another widely utilized remote access technique in REST and SOAP web API services. The COBRA technique’s primary goal is to ensure that several applications developed on different consoles, different programming languages, and specific hardware communicate. 

The COBRA technique is based on an object-oriented model. However, the applications that use COBRA need not be based on an object-oriented model. This technique uses a particular language, cakes Interface Definition Language (IDL). Any person using the COBRA technique needs to study the IDL language for implementation. 

The COBRA technique can be used on major operating systems, like Java, Linux, Windows, Android, Solaris, OS X, INTEGRITY, etc. Hence, it is independent of the operating system. Another advantage of the COBRA technique is transforming the data into the binary format and supporting data compression. 

  1. DCOM (Distributed Component Object Model):

Distributed Component Object Model (DCOM) was typically used remote access techniques in the REST architectural style and SOAP protocol. It is a Microsoft technology developed for establishing communication between systems or software segments. Earlier, the DCOM technique was referred to as Network OLE. 

The DCOM and CORBA techniques are quite similar, as both methods offer various distributed services. Any enterprise can use the DCOM technique within its private network. Also, it can work with several other networks. The protocols used by the DCOM technique are the HTTP Protocol and TCP/IP.

One of the pros of using the DCOM technique is supporting distributed shared memory management by providing interfaces. Further, it provides location transparency. Alternatively, there is no need for the client to know the component’s location. 

  1. Java RMI (Java Remote Method Invocation):

Java Remote Method Invocation (Java RMI) is a specially developed technique for Java Application Program Interface. It is compatible with working with only the Java Virtual Machine (JVM). Therefore, working with only JVM was the most significant limitation of the Java RMI technique. 

The primary goal of the Java RMI technique is that the object on the one Java Virtual Machine (JVM) invokes another object present on the other Java Virtual Machine (JVM). There are two terminologies used, called stub and skeleton. The stub is a gateway for the client, whereas the skeleton is a gateway for the server. 

The Java RMI method is object-oriented, which passes objects as arguments and provides return values. As Java offers WORA (Write Once, Run Anywhere) principle, Java RMI also supports this approach. 

The above four methods were commonly used remote access methods in REST and SOAP web API services. 


An application program interface behaves as a communication mediator between any two software applications or components. The web API is a mediator between web browsers and servers. The two most common web API services we discussed in this article are SOAP and REST. We have seen each of these two API services individually in detail. 

Later, we have gone through primary differences between the SOAP API and the REST API. The SOAP API is a protocol, whereas the REST API is an architectural style. Next, we covered some specific instances of using SOAP and REST APIs. In both the web API services, there are particular challenges. 

The SOAP API is more secure than the REST API, as it utilizes WS-Security, along with the HTTP protocol. On the contrary, the REST API is faster than the SOAP API because of JSON’s use. Lastly, we stated some commonly used remote access methods in REST and SOAP wen API service. 

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