REST and SOAP: When Should I Use Each (or Both)?

Web developers today have a myriad of technologies they can choose from; everything from simplified database access, to easy wrapping of existing middleware services, to a plethora of interesting client side software. All of these products and tools are there to give web developers the ability to create the best web-based applications in the shortest amount of time.

However, having a massive set of possible software solutions is one challenge, picking the specific approach for specific parts of the web applications is another, and web developers today have to juggle many of these decisions with changing standards or approaches seemingly appearing daily.

Take for example, the two approaches for interfacing to the web with web services, namely SOAP (Simple Object Access Protocol) and REST (Representational State Transfer). Both approaches work, both have advantages and disadvantages to interfacing to web services, but it is up to the web developer to make the decision of which approach may be best for each particular case.

By now, most developers have at least, from a periphery, been exposed to the REST approach, which uses a standard URI (Uniform Resource Identifier) that makes a call to a web service like http/ The approach is very simple to understand and can be executed on really any client or server that has HTTP/HTTPS support. The command can execute using the HTTP Get method. So developers that use this approach, cite the ease of development, use of the existing web infrastructure, and little learning overhead as key advantages to the style.

However SOAP, the granddaddy of all web services interfaces, is not going away anytime soon, and in fact with the introduction of SOAP 1.2 has fixed many of the perceived short-comings of the technology and pushing it to new levels of both adoption and ease-of-use. It should also be noted that the acronym SOAP no longer stands for Simple Object Access Protocol as of the 1.2 specification from the W3C organization; it is now just the name of the specification.

Now keep in mind that using SOAP 1.2 has some additional overhead that is not found in the REST approach, but that overhead also has advantages. First, SOAP relies on XML (Extensible Markup Language) in three ways; the Envelope – that defines what is in the message and how to process it, a set of encoding rules for datatypes, and finally the layout of the procedure calls and responses gathered. This envelope is sent via a transport (HTTP/HTTPS), and an RPC (Remote Procedure Call) is executed and the envelope is returned with information in a XML formatted document.

It is important to note that one of the advantages of SOAP is the use of the “generic” transport. While REST today uses HTTP/HTTPS, SOAP can use almost any transport to send the request, using everything from the afore mentioned to SMTP (Simple Mail Transfer Protocol) and even JMS (Java Messaging Service). However, one perceived disadvantage is the use of XML because of the verboseness of it and the time it takes to parse.

However, the good news for web developers is that both technologies are very viable in today’s market. Both REST and SOAP can solve a huge number of web problems and challenges, and in many cases each can be made to do the developers bidding, which means they can work across the domain.

But the untold story is that both technologies can be mixed and matched. REST is very easy to understand and is extremely approachable, but does lack standards and is considered an architectural approach. In comparison, SOAP is an industry standard with a well-defined protocol and a set of well-established rules to be implemented, and it has been used in systems both big and small.

So this means areas that REST works really well for are:

  • Limited bandwidth and resources; remember the return structure is really in any format (developer defined). Plus, any browser can be used because the REST approach uses the standard GET, PUT, POST, and DELETE verbs. Again, remember that REST can also use the XMLHttpRequest object that most modern browsers support today, which adds an extra bonus of AJAX.
  • Totally stateless operations; if an operation needs to be continued, then REST is not the best approach and SOAP may fit it better. However, if you need stateless CRUD (Create, Read, Update, and Delete) operations, then REST is it.
  • Caching situations; if the information can be cached because of the totally stateless operation of the REST approach, this is perfect.

That covers a lot of solutions in the above three. So why would I even consider SOAP? Again, SOAP is fairly mature and well-defined and does come with a complete specification. The REST approach is just that, an approach and is wide open for development, so if you have the following then SOAP is a great solution:

  • Asynchronous processing and invocation; if your application needs a guaranteed level of reliability and security then SOAP 1.2 offers additional standards to ensure this type of operation. Things like WSRM – WS-Reliable Messaging.
  • Formal contracts; if both sides (provider and consumer) have to agree on the exchange format then SOAP 1.2 gives the rigid specifications for this type of interaction.
  • Stateful operations; if the application needs contextual information and conversational state management then SOAP 1.2 has the additional specification in the WS* structure to support those things (Security, Transactions, Coordination, etc). Comparatively, the REST approach would make the developers build this custom plumbing.

As shown above, each technology approach has their uses. They both have underlying issues around security, transport layers, and the like, but they both can get the job done and in many cases, they each bring something to the web. So for this argument, the best rule, is the rule of flexibility, because no matter what the problem at least in today’s web development world, web developers have great solutions using either of these protocols.

About the Author

Mike Rozlog is the senior director of products for Embarcadero Technologies. In this role, he is focused on ensuring the developer focused products being created by Embarcadero meet the expectations of developers around the world. Much of his time is dedicated to discussing and explaining the technical and business aspects of Embarcadero’s products and services to analysts and other audiences worldwide. Mike was formerly with CodeGear, a developer tools group that was acquired by Embarcadero in 2008. Previously, he spent more than eight years working for Borland in a number of positions, including a primary role as Chief Technical Architect. A reputed author, Mike has been published numerous times. His latest collaboration is Mastering JBuilder from John Wiley & Sons, Inc.

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