WebService vs API

Modern software applications communicate with each other using two different techniques that are Webservices and application programming interface (API). Often, they are used interchangeably but they are built to serve different needs.

Webservices allow two machines to communicate with each other over the internet, whereas, API allows software applications to communicate with each other. API can be web based or it can exist within the same applications.

There are different approaches and standards followed to build both Webservices and APIs. Modern applications mostly use one of these standards to communicate with each other.

What is Webservice?

Webservice is a system designed to support machine-to-machine communication typically over the World Wide Web. It describes a standardized way of integrating two or more web applications using open standards such as XML, SOAP, WSDL, and UDDI. It uses Internet protocol in the background.

Organizations may have different software systems, and in such cases, they need to interact with each other. Webservices make it easier by allowing interchange of data and process it accordingly.

Additionally, two software systems can have an agreement in terms of the format and specifications of data being sent to each other.

Webservice Types

RESTful Web Services

REST stands for Representational State Transfer. RESTful Web services are more popular in modern application development and most used. As they have many unique features such as platform independence, faster compared to SOAP, data as a service approach, etc.

RESTful Web Services use JSON or XML format for communication. Webservices create an object and the state of the object is sent back as a response to the client’s request, this way they are known as Representational State Transfer.

SOAP Web Services

Simple Object Access Protocol popularly known as SOAP is a W3C recommendation for communication between two applications and allows lightweight XML-based data transfer between two systems. It is platform and language-independent. This allows it to interact with different applications even if they are written in two different programming languages. It provides an efficient and secure way to exchange data. It supports both stateful and stateless operations.

Webservices Features

• Webservices typically use XML as a standard data exchange format, they are lightweight and allow flexible coding and decoding irrespective of the programming languages and operating systems.
• Web Services support Remote Procedure Calls also known as RPC. It allows the program to invoke procedures and functions on remote objects.
• Web services, by design, support loose coupling, which means systems are loosely associated with each other. Also, it doesn’t care about the state of the system.
• Web Services can be both Synchronous and Asynchronous. RPC is an example of Synchronous communication, where the client will wait for the response from the server before the next operation. In Asynchronous web services, a client sends a request, and without waiting for the server’s response it continues with another operation.
• Web services provide high speed and reliability compared to other types of communication methods. Additionally, it is more secure.
• It provides a good level of code reusability, though the code reusability depends on the framework architecture, however, it provides the capability of reusability.

Disadvantages of Webservice

• Webservices are restricted for access from the browser, you need to build a specialized framework for communication
• Though web services look simpler, designing and architecting the web services demands proficient skill and knowledge.
• Webservices may not provide complete support for modern and emerging web technologies such as Web and AJAX, XML, HTTP etc.
• Webservices are highly secure, but security completely depends on implementation, and weak architecture may be more vulnerable.

What is an API?

An application programming interface (API) is an approach for computer programs or components to communicate with each other. A type of software interface offers service to other pieces of software. The API specification is a specialized document that describes how to build or use a connection or interface. API helps to provide an abstraction, without worrying about how it works internally, and how it is implemented. The programmer exposes only part of the code that is useful for the clients. An external or internal application that sends a request is called a client. A system that executes the requests and sends the response back is called a Server. The format or specification that two systems agree upon is called an API contract.

Types of API

APIs have a broad scope, they can be categorized in different ways such as by audience of types like public, private, open API, partner API, etc. If we categorize architecture, we can branch them into Monolithic, Microservices, Unified APIs, etc. It can also be segregated by Protocol. Below are the API types based on their protocol.

REST APIs

The Representational State Transfer API also known as REST APIs or RESTful APIs is most popularly used across web applications. It is popular because of its simplicity; it defines the routes with URLs, no need to wrap the URL with XML like any other protocol. However, REST APIs are limited to HTTP protocol, they can mostly send and receive text-based communications. Developers also perform specialized techniques to communicate non-text-based information by specifying the content type and performing text-based encoding to audio files, images, videos, etc.

SOAP APIs

The Simple Object Access Protocol also known as SOAP API is another major type of API protocol that communicates over major internet protocols such as TCP, HTTP, and SMTP. It is most flexible compared to REST APIs but it is more restrictive. They can only work with XML data and they have rigid requirements. They require more bandwidth and maintaining SOAP implementation code is more complex.

RPC APIs

The Remote Procedure Call also known as RPCS differs from SOAP and REST as it calls a method rather than a data resource. RPC APIs are mostly private APIs considering their security. During the RPC request process, it can change the state of the server so it is important to have a high level of security and trust between the producers and consumers. Google has tried to enhance the RPC protocol which is known as gRPC that uses Protocol Buffers to serialize and parse data. gRPC is built on HTTP/2 protocol.

GraphQL APIs

GraphQL was developed by Facebook, it is not a new API protocol, rather it’s a new approach to communicating. In REST APIs there will be multiple endpoints with different data schema. To get the desired response you may need to call specific endpoints. In GraphQL, there are typically single endpoints, but there will be unlimited data schemas available at that endpoint. A user should know available data fields, using those user can construct the queries and send them as payload using the HTTP protocol with the POST method, and then data is returned in the shape of the schema as per query sent as payload.

Features of APIs

• APIs are easy to implement, especially REST and GraphQL APIs are the most popular. They are simple to implement and easy to use.
• APIs hide the complexity involved in the back such as implementation, data flow, etc. and they expose only the required information to the user.
• APIs are good examples of modularity as individual components can be developed, tested, and maintained independently.
• Authentication, authorization, and data encryption are supported by APIs to ensure the security
• APIs support asynchronous operations which allow data to be processed in the background to improve application responsiveness.
• Caching reduces the API’s response time or latency and improves the performance of the applications considerably.

Disadvantages of APIs

• Depending on the implementation and security mechanism, APIs are more vulnerable compared to web services
• As the system grows dealing with dependencies, versioning, and changes in API specification can be more challenging and can increase the complexity
• API provides more flexibility, weak architecture may cause performance issues, and security issues, and there can be a risk of data privacy issues.
• As APIs evolve, keeping the versioning consistent, maintaining the documentation, testing them, and keeping them up to date can be challenging.

Webservices Vs APIs — Key differences

Webservices and APIs have many similarities but they have many distinct characteristics as well. Both are built to serve the unique needs of the user. The below table lists the key differences between Web services vs APIs

Web Service vs API — Which one to Choose?

APIs are most popularly used for modern web development; Web Services are used in legacy and enterprise-level integration. However, a better choice depends upon your requirements and features in scope.

Web Services are preferred in the below scenarios

• Webservices are preferred for enterprise-level system integration where security and reliability are critical such as financial systems, government organizations, healthcare systems, etc.
• If your application falls under regulatory compliance and policies and you need to maintain strict Standards and Protocols
• If your system requires to communicate between multiple operating systems and applications written in multiple languages
• If your organization has many legacy systems that are written in SOAP-based protocols and you want to maintain them

APIs are preferred in the below scenarios

• APIs are preferred for modern web development that focuses on faster performance and support across the web and mobile platforms
• If your organization follows modern microservice architecture and is built with RESTful APIs
• If you are looking for flexibility and simplicity.
• If you follow the DevOps ecosystem and modern agile methodology, you can test and deliver the individual components easily

How to perform test automation for APIs?

Different tools provide the capability to test the modern API’s, some tools provide options to test only API endpoints, and few tools provide options to test seamlessly both UI and API together.

Postman, Swagger, and RestAssured are a few tools that focus on API testing only. One of the major challenges with this tool is you cannot combine the UI and API test which also means that data cannot be validated at different layers.

Testsigma is an end-to-end tool that supports both functional UI and API tests. As an advantage of this, you can validate the data and logic across the different layers. For example, you can fetch the user details from the/user details API endpoint and validate them against the user details web page.

Additionally, Testsigma comes with a no-code approach which doesn’t demand technical knowledge. Both API and UI can be tested by anyone who has the basic knowledge. Testsigma can also help in integrating your test with CI/CD pipelines and thus helps to reduce time to market.

Key areas to consider while testing APIs

APIs are the foundation for any web application, the modern applications are built with many individual APIs to serve the single or multiple functionality. Below are a few things to consider while testing the API

• Ensure security parameters are correctly handled. Example — Token, Expiry time, authorization, authentication, etc.
• Validate the HTTP status codes such as 2XX, 4XX, and 5XX are returned as expected.
• Validate your response against the predefined schema. Any change in API contract may cause the failure to downstream systems so schema validation is very critical.
• If there is a static response ensure a response is thoroughly validated for correct responses
• Try sending different payloads, different method types and alter the URLs and ensure it is behaving as expected.

Conclusion

APIs and Webservices — both are built for unique purposes. Modern web applications mostly rely on the APIs with REST protocol as they are more flexible and easier to implement. Web services are still in use for enterprise-level applications where security, compliance, and standards need to be met. Both are useful while communicating with different systems, components, etc. However, the usage may differ based on the requirements. Remember, no matter which technology you use for development, unless it is thoroughly tested and validated against different scenarios, quality is not guaranteed.

In modern applications, Testing APIs may not be enough. As data flows through different layers, there is a high chance of data alterations. Tools like Testsigma provide the most advanced techniques to test. With Testsigma, API testing can be a part of your functional testing. Additionally, it also supports no-code automation testing, CI/CD integration, an AI-driven test suite for easy maintenance, etc. Choosing the right tool for testing is as important as choosing the right technology for development.