SOAP API

Rubleen Kaur
Last Updated: May 13, 2022

Introduction

Before moving on to the SOAP API, I want to ensure the beginners understand what an API is!

Whenever you come across a website that shows you a map with the exact location rather than just displaying the address, that application is communicating with Google Maps using a web API.  Now, what is this API?

An API (Application Programming Interface) is a form of agreement of web services on how they will be exchanging the data, which can be anything from your login credentials or your map locations. An API is a software module that is designed to perform a specific look. Most applications today need to communicate with different applications. The use of the API does this. 

There are mainly two different types of APIs available:

  • SOAP API
  • REST API

If you are a web developer, you might already know how vital these APIs are, as using them, you can integrate any data you want in your project.  So, now that you have revised a bit about APIs, let's come back to the hot topic -  the SOAP API's 

Now, SOAP stands for Simple Objects Access Protocol, an XML-based protocol for accessing web services over HTTP. It was built to ensure that the various programming languages can talk to each other and avoid external development setup.

What is SOAP?

There are a large number of applications that are built on different languages. Today, we can ensign our application in Java, .NET, PHP, and many other new languages. Exchanging data in the 21st century plays a vital role. But when we share data in these applications, the complexity of the core increases. One way to accomplish this is by the use of XML as an intermediary between the languages. An important point to remember is that All the programming languages understand the XML Markup Language. SOAP was developed to work with XML over HTTP and has some specifications that can be used with various languages. It is a protocol of how different web services should talk to each other or talk to client applications that call them. 

An essential feature of SOAP API is that it supports both stateful and stateless operations. Stateful operations mean that the Server keeps the information from the Client through multiple requests. On the other hand, Stateless Operations implies that an injunction should contain enough information to have a minimal dependency on the Server. 

SOAP is even recommended by the W3 Consortium, the governing body of all the web standards. SOAP is designed to be platform-independent and even OS-independent. It works with HTTP protocol that remains the same across all the platforms. 

Let’s see now how SOAP messages are structured and learn about each element. 

SOAP Message

A SOAP message is encoded as an XML document, which consists of an <Envelope> element, that contains an optional <Header> and a mandatory <Body> Element. 

In the body element, we also have an <Fault> element used for reporting errors in the application. 
 

 

Let's talk about the SOAP Envelope that is a mandatory element in all the SOAP messages. This element contains two child members, an optional header, and a required Body element. 

SOAP Header is an optional sub-element used to pass application-related information that is to be processed by soap nodes in the path. SOAP body is a mandatory sub-element in the envelope element which contains information intended for the ultimate recipient of the message.

Syntax rules you should follow while using a SOAP message are: 

  • SOAP messages are to be encoded using XML.
  • SOAP message should not contain a document type definition. 
  • In a SOAP message Envelope element is a must.
  • A SOAP message should not contain XML Processing Instructions.

Let’s consider this skeleton message example for a reference,

<?xml version="1.0"?>

 

<soap:Envelope

xmlns:soap="http://www.w3.org/2003/05/soap-envelope/"

soap:encodingStyle="http://www.w3.org/2003/05/soap-encoding">

 

<soap:Header>

...

</soap:Header>

 

<soap:Body>

...

  <soap:Fault>

  ...

  </soap:Fault>

</soap:Body>

 

</soap:Envelope>

 

SOAP extensibility with WS Standard Protocol

 

As seen in the above section, SOAP API provides a standard structure element of the message. The SOAP API does not provide any restrictions on what information goes inside these Headers and Body elements, and we can customize them according to our usage. 

A few standard protocols that cover the features and areas of SOAP are

  • Security
  • Messaging
  • Transactions
  • Meta Data, etc.

Web Services Description Language Document

The WSDL is an XML description of a web service. One of the essential features of SOAP APIs is that they always use a WSDL Document. These documents act as a guideline for communicating with a web service, as it defines the endpoints, which describe all the processes the exposed applications can perform. 

A WSDL document act as a signed contract between the Client and the Server.

<definitions name="EndorsementSearch"

  targetNamespace="http://namespaces.snowboard-info.com"

  xmlns:es="http://www.snowboard-info.com/EndorsementSearch.wsdl"

  xmlns:esxsd="http://schemas.snowboard-info.com/EndorsementSearch.xsd"

  xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"

  xmlns="http://schemas.xmlsoap.org/wsdl/"

>

 

  <!-- omitted types section with content model schema info -->

 

  <message name="GetEndorsingBoarderRequest">

    <part name="body" element="esxsd:GetEndorsingBoarder"/>

  </message>

 

  <message name="GetEndorsingBoarderResponse">

    <part name="body" element="esxsd:GetEndorsingBoarderResponse"/>

  </message>

 

  <portType name="GetEndorsingBoarderPortType">

    <operation name="GetEndorsingBoarder">

      <input message="es:GetEndorsingBoarderRequest"/>

      <output message="es:GetEndorsingBoarderResponse"/>

      <fault message="es:GetEndorsingBoarderFault"/>

    </operation>

  </portType>

 

  <binding name="EndorsementSearchSoapBinding"

           type="es:GetEndorsingBoarderPortType">

    <soap:binding style="document"

                  transport="http://schemas.xmlsoap.org/soap/http"/>

    <operation name="GetEndorsingBoarder">

      <soap:operation

        soapAction="http://www.snowboard-info.com/EndorsementSearch"/>

      <input>

        <soap:body use="literal"

          namespace="http://schemas.snowboard-info.com/EndorsementSearch.xsd"/>

      </input>

      <output>

        <soap:body use="literal"

          namespace="http://schemas.snowboard-info.com/EndorsementSearch.xsd"/>

      </output>

      <fault>

        <soap:body use="literal"

          namespace="http://schemas.snowboard-info.com/EndorsementSearch.xsd"/>

      </fault>

    </operation>

  </binding>

 

  <service name="EndorsementSearchService">

    <documentation>snowboarding-info.com Endorsement Service</documentation

    <port name="GetEndorsingBoarderPort"

          binding="es:EndorsementSearchSoapBinding">

      <soap:address location="http://www.snowboard-info.com/EndorsementSearch"/>

    </port>

  </service>

 

</definitions>

 

SOAP WS-Security

 

The SOAP API is widely appreciated for integrating the WS-Security feature. Let's learn more about the same in this section.

Now the question is, what is this WS-Security?

→ The WS-Security is a set of protocols that determines how to implement the security inside a transaction and suggests data privacy and integrity. The protocol also allows encryption and authentication, and it even allows cryptographic signing.

WS-Security allows your message to be encrypted not just by HTTPS, but it also protects on the message level, which has the authentication data in the header elements. This message-level security is why financial organizations and other corporate users implement SOAP. 

 

 

Well, since we have covered almost all the features provided by the SOAP API, there are a few disadvantages you should consider.

Disadvantages of SOAP to consider

  • Resource consuming: Due to the large size of the XML-File and the payload created by the massive structure of the SOAP message, a SOAP API requires a large bandwidth.
  • Hard Learning Curve:  As the API is protocol-based, API servers are built to require the knowledge and understanding of all the protocols one might use. 
  • Lacks Flexibility: As we have already stated, the API serves a rigorous contract between the Client and the Server. The rigid structure of the SOAP API schema requires an additional effort for adding or removing any message properties on both sides of the communication, which makes the update process very tedious. 

All the resources you might need for SOAP. 

If you are a beginner, some of the resources available for SOAP API you should check out are

  • SOAP Documentation - This serves as a critical source for beginners. 
  • SOAP Versions - There are various versions of the protocol; you can check them out from here. 
  • WSDL - This is a key to learning how to use the Web Services Description Language and create the WSDL documents. 
  • WS-Security - This guide will help you learn how to enable message-level protection.

 

FAQs

  1. What is the SOAP API?
    SOAP stands for Simple Objects Access Protocol, an XML-based protocol for accessing web services over HTTP. It was built to ensure that the various programming languages can talk to each other and avoid external development setup. SOAP was developed to work with XML over HTTP and has some specifications that can be used with various languages. It is a protocol of how different web services should talk to each other or talk to client applications that call them. 
     
  2. What is the anatomy of a SOAP message?
    A SOAP message is encoded as an XML document, which consists of an <Envelope> element, that contains an optional <Header> and a mandatory <Body> Element. In the body element, we also have an <Fault> element used for reporting errors in the application.
     
  3. What is WS-Security?
    The WS-Security is a set of protocols that determines how to implement the security inside a transaction and suggests data privacy and integrity. The protocol also allows encryption and authentication, and it even allows cryptographic signing.
     

Key Takeaways

Hey everyone, so let’s brief out the article. 

  • This article has explained SOAP API, its uses. The SOAP API is an XML-based protocol for accessing web services over HTTP.
  • We have discussed the SOAP Message Structure which includes, an XML document, which consists of an <Envelope> element that contains an optional <Header> and a mandatory <Body> Element. In the body element, we also have an <Fault> element used for reporting errors in the application.
  • Further, we have seen the WSDL Documents and how we can use the WS-Security.

Isn’t Web Development engaging? Building new websites and using amazing animations and different APIs, don’t be scared if you cannot grasp the hold of this vast development. We have the perfect web development course for you to make you stand out from your fellow developers. 

Happy Learning Ninjas!

 

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