Web Service vs API – What are they & How do they Differ?

Web Services and an Application Programming Interface(API) provide web communication functionality. Though they provide similar functionalities they are not the same. Many channels sometimes use the Webservice and API interchangeably but they are different. They exist to solve different challenges. In Short, API allows the application to communicate while web service allows the system to communicate with each other. The difference between web services vs API can help to understand each of them clearly.

What is an API?

An application programming interface (API) is a set of rules that define how applications can communicate with each other. There are different types of APIs like GraphQL, REST, WebSocket APIs, RPC APIs, etc. All APIs have their own set of protocols and definitions. So each API type operates differently. 

API is simple to implement and will have a lightweight architecture. It is often assumed that APIs are web APIs, that is information is exchanged over the internet. However, APIs can also be exposed using local files such as JAR without the internet. Web APIs are the most common and widely used.

Components of API

APIs are very lightweight, it involves three main components.

• Client: A client can be any external or internal application that makes the request.
• Server: A server executes the program and sends the response.
• API contracts: Request response formats are also known as API contracts.

Types of APIs

Below is the list of different types of APIs

• REST-based APIs: It is a browser-compatible API that uses the Uniform Resource Identifiers and HTTP protocol for communication. Data is exchanged using the JSON format.
• SOAP-based APIs: It uses the Simple Object Access Protocol and XML for the exchange of data. This is more secure compared to REST-based APIs
• GraphQL-based APIs: It is an advanced web-based API. Open-source data query and manipulation language are used.
• XML-RPC: It uses minimal bandwidth. A specially designed XML format is used for transferring data. Compared to SOAP, the XML RPC offers a more simplified way.
• WebSocket: Two-way interactive communication session is established. More helpful if your application needs event-driven responses.

  Features of API

• Simple: The APIs are easy to implement and maintain. Consuming API is even more, simpler developer doesn’t need to know the internal implementation.
• Flexibility: API provides the flexibility to reuse. APIs can have dependent calls which means that API implementation code can call another API.
• Security: APIs can be implemented and exposed securely using authorization and authentication mechanisms.
• Language-independent: It is language-independent that is if API can be implemented in Java. The client can access those APIs using C# code.

Advantages of API Services

• API improves connectivity
• It supports traditional CRUD operations (Create, Read, Update, Delete)
• Works with HTTP verbs such as PUT, DELETE, POST, GET, PATCH, UPDATE
• Service data can be exposed to the browser
• APIs can be easily integrated with Graphical User Interface (GUI)
• APIs support a high level of customization
• APIs can be restricted with authentication and authorization
• Supports multiple formats like XML, JSON, etc. or you can use your custom formats

Disadvantages of API

Just like any other software component, APIs have some drawbacks. 

• Creating API endpoints requires expertise skills in the programming language
• API maintenance cost is high
• API  Requires a fixed scale
• To support scalability, you might end up incurring high infra-cost

What is a web service?

Web service is a software system designed to support interoperable machine-to-machine communication over the Internet. Web services are designed to provide a specific set of services. Developers can utilize multiple web services to build a single functionality which helps in code reusability and reduces the time and cost of development.

Webservices require a network to interact and network communication is generally achieved using Simple Object Access Protocol (SOAP). SOAP uses XML format for encoding data. The XML format is used for storing and transferring information using HTTP protocol. 

An application sends the requests to a service in XML format. Services then see and process the request and reply to the application as response using the same XML format. Web services can follow SOAP or REST principles for implementation. However, SOAP is the most widely used.

Types of Webservices

Web Services can be broadly classified into two different types as given below

• SOAP Web Service: SOAP is a legacy protocol. Designed before REST.  SOAP became popular as it provides an efficient and secure way to exchange data independent of the software platform.

• REST Web Services: REST is more helpful when your application requires manipulation or exchange of media files, objects, or objects on a hardware device. The service needs to fully adhere to REST principles to claim the service as a RESTful service. The HTTP verbs such as GET, POST, PUT, and DELETE are used as commands for information exchange.

Features of Web Services

• Web services make it easier to exchange document
• Web service can function synchronously or asynchronously
• It supports remote procedure calls (RPC)
• It is loosely coupled
• Encourages modular design principles

Advantages of Web Services

• Web Services are easy to use
• Well, architecture web services provide a high level of code reusability.
• It enables both communication and data exchange
• Increased speed within or outside the organization
• It perfectly fits into the agile model
• Webservices are the most flexible and secure
• Webservices are platform independent

Disadvantages of Webservice

• Web services cannot be accessed directly from the browser
• The highly skilled resource is required to design the web service
• You cannot leverage emerging web technologies such as Semantic Web and AJAX XML HTTP
• Though web services provide security elements however it completely depends on effective implementation.
• HTTP protocol can be unreliable

Differences between Web Services and API

Web Service	API
Web service is a type of API	API is an interface that helps in communication between two applications.
All web services must be accessed through the network	API may or may not be accessed through the network (Based on design).
Web services can use REST, SOAP, and XML-RPC for communication.	There is no specific type of communication. API can use any style of communication
The information exchange is carried out using the XML format	The API response can use any format such as XML, JSON, or custom type
Webservice is heavy in comparison with the API as it uses SOAP and XML for data exchange	API is very lightweight
Web services support HTTP protocol	It supports HTTP and HTTPS along with header values for request/response
Webservices allow machines to communicate	APIs allow applications to communicate
Follows complicated and legacy implementation approach	Simple and follows a modern implementation approach

 

How to do API test automation with Testsigma?

As many organizations are following API-driven development, it is important to test the API. API testing is not as easy as we think. API testing requires some level of technical expertise as you need to pass the request body, headers, authorization token, etc. Testsigma makes its simpler using the No Code method.

Steps to Create API Tests in Test Sigma

Step 1: Log in to TestSigma

Step 2: Click Create Test Case  and Enter the required Details

Step 3: Add RESTFUL API 

Step 4: In the REST API window, enter the required details and Click on Create

If you are using any tool other than Testsigma, you need to construct the whole request details using the programming languages which includes headers, URL, request body, etc. However in TestSigma its just a few clicks.

Automate your API tests, the codeless way, Testsigma

What to Test in API Testing?

API Testing is most critical as it is the middle layer. APIs usually communicate with UI and Database. You can test a lot more in API testing. However, at the minimum, you need to test below key areas.

• Response Code
• Response Payload
• Response headers
• API Contracts

Remember, While doing API testing you need to focus on both happy flows, sad/error flows, and edge case scenarios.

It is recommended to perform API testing as much as possible. Compared to UI tests API test are more stable and takes less time to execute. The data and major chunk of application functionality can be tested using API testing.
The web service and APIs are not the same, they exist to solve different problems. The modern web application architecture emphasizes API-driven development. So web APIs are most commonly used across the industry. API also simplifies complex application development and helps in code re-usability and security. API can be implemented in different ways based on needs and other organization-related factors. As the development is aligning with web API the need for API testing is more. Most organizations follow API testing as integration testing as major data-related functionality can be tested within a few minutes. Most of the automation tools support API testing however, setting up an API testing framework takes more time. Importantly, the requirement for skilled resources is a major challenge. Tools like Testsigma make API testing easier and faster. It also comes with DevOps (CI/CD) integration thus it makes developer/tester friendly.

Frequently Asked Questions

Is web service and REST API the same?

Though many of us use the web service and API interchangeably it is not the same. Webservice is the legacy approach used for exchanging data between systems or applications. The REST API is used to interact between two applications.

What is an example of a web service and API?

A payment gateway is an example of a web service. You might have seen login with Google/Facebook etc. while you sign up when you choose Internally it uses the respective organization APIs for authentication.