Web Service vs. REST API, Compared In Depth with Examples

Recent years have seen a significant improvement in software development thanks to API-based infrastructures and service platforms. Examples of these service platforms are Amazon Web Services (AWS) and Google Cloud Platform (GCP). These independent technologies, web services, and application programming interfaces (APIs) can appear to have similar purposes, raising misconceptions among beginners.

Someone who's just starting to learn about web services and APIs might ask, "Is a REST API a web service? What are the differences between a web service and an API?" Questions like these require clarifications that expose the nature of these technologies. This article will provide point-blank answers to the highlighted questions about the nature of APIs and web services.

What are APIs?

An API is a medium for two or more computing devices to communicate with each other. Chiefly, it provides a set of functions or procedures to build or integrate functionalities into a piece of software.

Conventionally, APIs are categorized mainly by release policies (public, private, internal), specifications (the standard categorization, SOAP, REST, RPC), and use cases (database, operating system, remote, and web APIs). Following the most common categorization, we'll discuss APIs classified by their design.

Types of APIs by Design

• Simple Object Access Protocol (SOAP): This protocol uses XML (Extensible Markup Language) as its message format for requests and responses over HTTP or SMTP. XML is generally considered more human-readable compared to its alternatives, but it comes with the issue of bandwidth, making the SOAP protocol require more resources for communication.
• Remote Procedure Call (RPC): RPC, like SOAP, is a protocol by design. It supports XML and JSON for messaging. Also, It separates the messaging format into types named XML-RPC and JSON-RPC, respectively. Recently, Google released an open-source RPC framework, gRPC, that supports XML, JSON, and protocol buffers (a language-neutral mechanism for storing and transmitting structured data).
• REpresentational State Transfer (REST): REST is an architectural style and design employed in API development. It consists of six guiding constraints for building applications that communicate over HTTP. It supports multiple messaging formats, including HTML, XML, YAML, JSON, and plain text, providing more flexibility and a wide range of use cases. Primarily, REST uses JSON for data exchange. Additionally, REST is a lightweight and performant API architecture that has gained acceptance among developers over the years in software development. This is because it uses significantly less bandwidth when transferring data in JSON format.

Another term associated with APIs is GraphQL. In contrast to the API types listed above, GraphQL is a query language for APIs intended to enhance performance and usability. The ideology behind this design approach for APIs is beyond the scope of this article.

APIs You're Already Familiar With

You might not have known it, but you've probably interacted with several APIs just today. At their core, APIs are ways for users to communicate with a company's systems and get data. Here are some APIs you may have used today:

• Google maps API for searching locations and getting directions
• GitHub API for retrieving data, automating software development workflows, and establishing integrations with third-party applications
• OMDB API for retrieving information about movies

Now that we've discussed what APIs are, let's turn our attention to web services.

What Are Web Services?

A web service is a technology or software that provides specific functionalities for use between machines over standard web protocols with XML as its messaging format. The communication interface for a web service is described with Web Service Description Language (WSDL), an XML-based document used to describe the functionalities provided by a web service. Additionally, web services are built on service-oriented architecture (SOA), giving room for reusability and interoperability.

Amazon Web Services and Google Cloud Platform have made web services more available to the public. They aid computing processes like document storage, analytics, database management and provisioning, machine learning, and more. Occasionally, a web service can integrate with another web service to serve a purpose. For example, a company can deploy a machine learning model with Amazon SageMaker that reads data from Amazon Redshift.

Types of Web Services

• SOAP: SOAP in web services is the same as SOAP in APIs—it's an XML-based protocol for communication over HTTP. It provides XML-based access to web services over HTTP/S, SMTP, and other supported protocols, including SMTP.
• XML-RPC: The XML-RPC protocol is similar to SOAP in the messaging format. The major difference between them is that XML-RPC only works on HTTP/S connections.
• REST: RESTful web services leverage the REST architectural style discussed earlier to provide access to their resources. Similarly, they use JSON as their primary data exchange format.

Examples of Web Services

Following the definition and nature of web services, it should be clear that they serve as an interface to a resource server and provide the functionalities of the server to users. Examples of these web services include:

• Amazon S3 for storage
• Amazon Redshift and Google Big Query for data warehousing
• Amazon Elastic Container Search (ECS) for containerization
• Amazon Elastic Kubernetes Search (EKS) for running Kubernetes
• Google Firestore for storage
• AWS Amplify and Google Firebase for deploying web and mobile applications
• Google Analytics for analytics monitoring on web and mobile

Most of these services provide a medium for users to access them through programming languages via their software development kits (SDK) or other means. Recently, some web services provided API endpoints to access their functionalities. An example is Amazon S3, although the document recommends that you use their SDK.

Differences between Web Services and APIs

Web services and APIs are pretty similar, but there are some important differences. The main difference is that a web service is a network-based resource that provides machine-to-machine interaction by interfacing between the machines. An API provides application-to-application interaction by providing the data and functionality of one for another to build on.

It's important to note that an API may or may not require an internet connection. It can be deployed on the same server as the consumer (e.g., localhost), which doesn't require an internet connection. However, most public APIs are deployed on remote servers and require an internet connection for use. On the other hand, web services require an internet connection in all cases.

Another difference is that a web service might require complex authentication gateways to define access levels, but APIs stick to standard authentication mechanisms for ease of use.

Also, web services are modular and interoperable. They can be coupled into complex services, and because they were established using service-oriented architecture, they effectively interact. APIs, on the other hand, offer data and functionality to an external program; due to their nature, they cannot be grouped to communicate with one another.

Lastly and chiefly (you may have pieced this together already): a web service is an API, but not all APIs are web services.

Final Thoughts

A web service is an API, but not all APIs are web services. This article has helped you to understand why the previous statement is true. You've learned about the definition and nature of web services and APIs, how they inherently facilitate software development, and their differences.

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