APIs keep applications connected and help provide a dynamic experience for users. Learn more about these two types of APIs.
Most webpages and operating systems rely on APIs (Application Programming Interfaces) — kind of like our bodies’ fascia; they keep digital tools connected and communicating. People constantly use APIs and without realizing it. They help us do things like transfer funds online, get boarding passes, embed videos on websites, and get accurate shipping estimates when shopping online.
A quick look at APIs
An API is a type of software that allows mobile and web applications to “talk” to each other using a set of rules, definitions, and protocols.
Modern APIs are typically developer-friendly, somewhat standardized, and versatile. These days, APIs are designed and documented much as a product would be.
Real-world API examples:
AccuWeather’s APIs provide accurate weather data for locations across the planet, helping customers update users with timely, local weather information.
Google Maps APIs allow businesses to pull and analyze local data or send directions to customers or delivery services.
PayPal APIs make online payments and transfers quick and secure.
If you’re interested in a career in tech, understanding APIs can help you get ahead. Even if you’re not a developer, you may need to know what they do in order to collaborate for projects.
There are two main types of API protocols: SOAP and REST. Here, we’ll dig into the best use cases, advantages, and disadvantages of each:
SOAP basics
Built for Microsoft in 1998, SOAP (Simple Object Access Protocol) uses XML technology and (usually) HTTP (hypertext transfer protocol) to create a framework for sharing information easily and efficiently. This means two applications, running on different operating systems, can communicate despite using different technologies and programming languages.
This built-in functionality is why SOAP web services are best known for being language- and platform-independent.
SOAP protocol provides an extremely secure method of information transfer, designed to bring stability and consistency to the data exchange process. SOAP messages are packaged and sent in envelopes. The envelopes contain the necessary information for processing requests. Header and body attributes are crucial parts of the SOAP envelope.
What does a SOAP request message look like?
A SOAP request message is sent to the provisioning client as a series of ASCII (American standard code for information interchange) characters. Then, the provisioning client sends back a SOAP response message.
A SOAP message consists of:
An <Envelope> element (contains an optional <Header> element)
A <Body> element
A <Fault> element (in <Body>) used for reporting errors
This is a reliable messaging system between services interfaces, thanks to SOAP’s strict adherence to ACID properties — Atomicity, Consistency, Isolation, and Durability.
Disadvantages of SOAP API
SOAP is more secure, but it lacks flexibility — SOAP only supports XML. And it’s definitely more complex to work with, so newer developers may have a harder time with SOAP. And because SOAP uses more bandwidth, it may take your web browser a little more time to process.
Here are a few drawbacks you might encounter with SOAP:
Because SOAP depends on WSDL* (Web Service Description Language), it’s not recommended for loose-coupled applications.
SOAP is difficult to test in browsers.
SOAP clients do not hold any stateful references to remote objects.
SOAP API calls are not cached.
*The WSDL document contains information such as the data formats used in SOAP messages and the functions provided through the web service.
REST Basics
REST (Representational State Transfer) is a completely different approach that relies on simple URLs. It’s a software architecture style that uses a stateless communications protocol — usually HTTP. It’s more manageable and less complex to code, and REST APIs are super flexible. REST is a simple, lightweight way to integrate applications.
REST APIs use resources, any kind of object, data, or service that can be accessed by the client. REST can be used to request resources, modify, and add new items on a server using HTTP methods.
When a request is made using REST, the server transfers a standardized version of the current state of the resource (i.e., all relevant information is packaged in a format that clients can easily interpret).
Something to note: REST is independent of any underlying protocol, and isn’t necessarily tied to HTTP. It could also use something such as FTP (File Transfer Protocol) or SMTP (Simple Mail Transfer Protocol). And REST allows data to be delivered in multiple formats, including plain text, HTML, XML, and JSON.
What’s the difference between XML and JSON?
For a while, XML was the only choice for open data interchange (and SOAP contributed to its popularity). But with the rise of REST APIs, JSON started gaining momentum. XML and JSON are slightly different.
XML is a language to specify custom markup languages (provides more than data interchange). It was designed to carry, not display, data. XML offers metadata support, mixed content support, and browser rendering.
JSON is a data interchange format (provides data encoding specification). JSON is a format based on JavaScript programming language and is easy to understand and generate. JSON is typically smaller, less verbose, and (for obvious reasons) fits easily into JavaScript code.
Both XML and JSON are human-viewable text formats and can be parsed.
What’s the difference between REST and RESTful APIs?
REST is a set of constraints, and RESTful is an API that adheres to REST architecture constraints. RESTful consumes very little bandwidth. RESTful web services allow client-server separation so each part can evolve independently. This means changes made on the server side won’t affect client application.
REST vs RESTless
Uniform interface is a key constraint that differentiates a REST API from a RESTless API. This constraint is fundamental to the design of REST.
Briefly, here are a few guiding principles of uniform interface:
HATEOAS (hypermedia as the engine of application state): It allows the client to navigate to the appropriate resources via hypermedia links.
Identification of resources: Naming and identifying the resources makes the service more useful and easier for developers to work with.
Self-descriptive messages: Each message contains all the information the recipient needs to understand it.
Disadvantages of REST API
While REST APIs are flexible, the lack of state, such as within sessions, can be troublesome since many web apps require stateful mechanisms (being stateless means each request should contain all the information required to process it, more on this later).
Also, because REST is a set of guidelines, it can be implemented in a variety of ways. This can lead to inconsistencies and confusion for developers.
REST is synchronous in nature.
Sessions can't be maintained.
REST-based applications can be restricted by HTTP protocol.
REST is less secure.
What is the difference between SOAP and REST API?
The key difference is that SOAP is a protocol and REST is an architecture.
SOAP exposes components of application logic as services rather than data. It performs operations through a standardized set of messaging patterns. REST is used to access data; it operates through an interface to access resources.
Let’s take a look at a few other differences between the two types of APIs:
Why is SOAP more secure than REST?
Because of SOAP’s secure nature, it’s recommended for projects such as high-security apps, financial services, and payment gateways. But what makes SOAP so much more secure than REST?
Both SOAP and REST use SSL (secure sockets layer) security. But unlike REST, SOAP supports WS-Security (web standard security) for enterprise-level protection. WS-Security specifies how security measures are implemented in web services to protect them from external attacks. This set of protocols ensures security for SOAP-based messages using tokens and authentication to ensure confidentiality.
Why does SOAP require more bandwidth than REST?
Due to the larger size of an XML file (and the payload created by the structure of a message), a SOAP API requires a larger bandwidth. REST was designed to be more lightweight and takes up less bandwidth.
What’s the difference between stateless and stateful?
Stateful and stateless applications differ in whether or not they store data.
Stateful: Saves data generated in a session and uses that data the next time the client
makes a request.
Stateless: Does not save client data generated in a session — requires backing storage.
When to use SOAP vs REST API
Wondering whether you should use SOAP or REST? They both have pros and cons, so it really depends on your project. If SOAP is the envelope, REST is more like a notecard or sticky note. Each has its place: one is more secure, the other is easier to scale.
What are the advantages of SOAP over REST?
The top benefit of SOAP APIs is the security, but SOAP does offer a few other advantages:
Works well in distributed environments
Protocol neutral (works with HTTP, SMTP, TCP, or JMS, for example)
Standardized
Built-in error handling
ACID-compliant
More extensibility
What are the advantages of REST over SOAP?
REST APIs are lightweight and easier to scale. REST APIs also offer:
A smaller learning curve — and a lot more free tutorials
Efficiency (SOAP uses XML for all messages, REST mostly uses smaller message formats like JSON)
Faster processing
Flexibility (can collect server data in multiple formats)
Cacheable responses (REST services use server-side caching and client-side caching.)
Fewer requirements for external libraries on the client side
Use SOAP if…
If your aim is to build an enterprise-level web service, SOAP is likely a better fit thanks to its security. SOAP is a good bet for:
Developing private APIs (again, especially for large enterprises).
More security features.
Seamless processing of stateful operations.
Formal means of communication (ideal due to its in-depth regulations).
Integrating with legacy systems that already use SOAP.
Use Rest if…
If you need a lightweight, scalable solution, REST might be a better option. Consider REST if you’re:
Developing public APIs (when heightened security isn’t a top concern).
Working with limited resources, lack of time, or bandwidth restrictions.
Handling many requests.
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