Web services provide a platform-independent and language-neutral mechanism for applications and devices to interact with each other over the World Wide Web. There are two types of web services mainly - SOAP and REST.
SOAP (Simple Object Access Protocol) is a protocol that uses XML format for exchanging data and it defines a set of rules on how to transmit and receive this XML data. SOAP is a more traditional, heavyweight web service typically used in enterprise environments where security and reliability are paramount.
REST (REpresentational State Transfer) is a set of design rules to exchange data over the internet using simple HTTP messages. REST is a lightweight alternative to SOAP that uses HTTP requests to exchange data in JSON format.
SOAP vs REST
Both SOAP and REST can be used to create web services and expose data and functionality from a variety of applications. They are also platform independent and can be written in any programming language.
Because SOAP uses XML for its messaging format, it can be quite verbose and large in size. This can make SOAP web services slower than their REST counterparts. However, the extra overhead of XML can also make SOAP messages more resistant to tampering and better able to withstand attacks.
REST web services are usually used in mobile or web applications where performance is important. The lightweight JSON messaging format makes REST messages smaller and faster than SOAP messages. However, because JSON is not as strongly typed as XML, it can be easier for malicious users to tamper with REST messages.
SOAP and REST both have their place in the world of application development. It's important to choose the right tool for the job at hand, taking into account the specific needs of your project.
How SOAP works
A SOAP client generates a request which is an XML document (also known as a SOAP Message) and sends it to a SOAP Server using HTTP or HTTPS protocol. The server responds with a XML document(SOAP Message) that contains the data requested by the client.
SOAP Message Structure
A SOAP message is an XML document which contains a set of XML elements arranged in a tree structure. The structure of a SOAP message is depicted in the figure below.
SOAP Envelope: At the root of the SOAP message is the <Envelope> element and it is mandatory. It consists of an optional <Header> element and the mandatory <Body> element
SOAP Header: The <Header> element is a child element of the <Envelope>. It is optional and if exist, it must be the first child element of Envelope and contains application related information that is used for processing the message.
Header Blocks: <Header> element can have one or more child elements and these are called Header blocks. Header blocks can be SOAP defined attributes or application defined attributes. Few examples of SOAP defined attribute are
encodingStyle,actor,mustUnderstandandrelay.SOAP Body: The <Body> element is a mandatory element and contains the data that is exchanged between the SOAP sender and receiver.
Fault: The <Fault> element is a child element of Body and is used for reporting errors that occur while processing the SOAP message. This element is optional.
How REST works
REST (Representational State Transfer) is a set of architectural guidelines for building web services. It is based on a client-server model, where the client sends a request to the server and the server responds with data or an action. Web services that follow REST architecture are called RESTful Web Services. RESTful web services are built using HTTP and follow a set of constraints, such as being stateless and having a uniform interface. The most common HTTP methods used in RESTful web services are GET, POST, PUT, and DELETE, which correspond to the CRUD (Create, Read, Update, and Delete) operations. RESTful web services typically return data in a format such as JSON or XML.
A RESTful web service must adhere to the following key principles.
Separation of concerns between client and server: The client is responsible for handling the user interface and user interactions, while the server is responsible for handling the business logic and data storage. The client and server are decoupled, meaning they do not have to be aware of each other's implementation details.
Stateless Communication: The server should not maintain any client context between requests. This means that each request made by the client to the server should contain all the information necessary for the server to understand and process the request. The server should not rely on any information or state that was present in previous requests.
Identification of resources: Each resource should be uniquely identifiable via a URI (Uniform Resource Identifier).
Manipulation of resources through representations: Resources can be manipulated through the exchange of representations, such as JSON or XML. The client can retrieve a representation of a resource using the GET method, and update a resource by sending a new representation using the PUT or PATCH method.
Self-descriptive messages: Each message sent by the client or server should include enough information to understand the request or response, such as the HTTP method, URI, headers, and body.
Cacheable: Responses from the server can be cached by the client, reducing the number of requests and improving performance.
Layered Design: A REST API can be composed of multiple layers, such as a load balancer, web server, application server, and database. Each layer can be replaced or updated without affecting the others.
Hypermedia as the engine of application state (HATEOAS): The API should include links to other resources in the responses, allowing the client to navigate the API and discover new resources.
Web services are a powerful tool for connecting different systems and applications over a network. They allow different systems to communicate and exchange data using standard protocols such as HTTP and XML. This article discusses two main types of web services - SOAP and REST, and how they work to provide an API for integrating different a system's.
