Compare RESTful Vs SOAP

Understanding SOAP and REST Basics

 

Simple Object Access Protocol (SOAP) and REpresentational State Transfer (REST) are two answers to the same question: how to access Web services. The choice initially may seem easy, but at times it can be surprisingly difficult.

SOAP is a standards-based Web services access protocol that has been around for a while and enjoys all of the benefits of long-term use. Originally developed by Microsoft, SOAP really isn’t as simple as the acronym would suggest.

REST is the newcomer to the block. It seeks to fix the problems with SOAP and provide a truly simple method of accessing Web services. However, sometimes SOAP is actually easier to use; sometimes REST has problems of its own. Both techniques have issues to consider when deciding which protocol to use.

Before I go any further, it’s important to clarify that both SOAP and REST are protocols: a set of rules for requesting information from a server using a specific technique. The rules are important because without rules, you can’t achieve any level of standardization. The best way to view a protocol is as if it is a diplomat who is making a request on your behalf from another entity. Some people I’ve talked with just don’t understand the entire concept; they have the idea that some sort of magic is occurring. Both SOAP and REST rely on well-established rules that everyone has agreed to abide by in the interest of exchanging information.

A Quick Overview of SOAP

SOAP relies exclusively on XML to provide messaging services. Microsoft originally developed SOAP to take the place of older technologies that don’t work well on the Internet such as the Distributed Component Object Model (DCOM) and Common Object Request Broker Architecture (CORBA). These technologies fail because they rely on binary messaging; the XML messaging that SOAP employs works better over the Internet.

After an initial release, Microsoft submitted SOAP to the Internet Engineering Task Force (IETF) where it was standardized. SOAP is designed to support expansion, so it has all sorts of other acronyms and abbreviations associated with it, such as WS-Addressing, WS-Policy, WS-Security, WS-Federation, WS-ReliableMessaging, WS-Coordination, WS-AtomicTransaction, and WS-RemotePortlets. In fact, you can find a whole laundry list of these standards on Web Services Standards.

The point is that SOAP is highly extensible, but you only use the pieces you need for a particular task. For example, when using a public Web service that’s freely available to everyone, you really don’t have much need for WS-Security.

The XML used to make requests and receive responses in SOAP can become extremely complex. In some programming languages, you need to build those requests manually, which becomes problematic because SOAP is intolerant of errors. However, other languages can use shortcuts that SOAP provides; that can help you reduce the effort required to create the request and to parse the response. In fact, when working with .NET languages, you never even see the XML.

Part of the magic is the Web Services Description Language (WSDL). This is another file that’s associated with SOAP. It provides a definition of how the Web service works, so that when you create a reference to it, the IDE can completely automate the process. So, the difficulty of using SOAP depends to a large degree on the language you use.

One of the most important SOAP features is built-in error handling. If there’s a problem with your request, the response contains error information that you can use to fix the problem. Given that you might not own the Web service, this particular feature is extremely important; otherwise you would be left guessing as to why things didn’t work. The error reporting even provides standardized codes so that it’s possible to automate some error handling tasks in your code.

An interesting SOAP feature is that you don’t necessarily have to use it with the HyperText Transfer Protocol (HTTP) transport. There’s an actual specification for using SOAP over Simple Mail Transfer Protocol (SMTP) and there isn’t any reason you can’t use it over other transports. In fact, developers in some languages, such as Python, are doing just that.

A Quick Overview of REST

Many developers found SOAP cumbersome and hard to use. For example, working with SOAP in JavaScript means writing a ton of code to perform extremely simple tasks because you must create the required XML structure absolutely every time.

REST provides a lighter weight alternative. Instead of using XML to make a request, REST relies on a simple URL in many cases. In some situations you must provide additional information in special ways, but most Web services using REST rely exclusively on obtaining the needed information using the URL approach. REST can use four different HTTP 1.1 verbs (GET, POST, PUT, and DELETE) to perform tasks.

Unlike SOAP, REST doesn’t have to use XML to provide the response. You can find REST-based Web services that output the data in Command Separated Value (CSV), JavaScript Object Notation (JSON) and Really Simple Syndication (RSS). The point is that you can obtain the output you need in a form that’s easy to parse within the language you need for your application.

As an example of working with REST, you could create a URL for Weather Underground. The API’s documentation page shows an example URL of http://api.wunderground.com/api/Your_Key/conditions/q/CA/San_Francisco.json. The information you receive in return is a JSON formatted document containing the weather for San Francisco. You can use your browser to interact with the Web service, which makes it a lot easier to create the right URL and verify the output you need to parse with your application.

 

Deciding Between SOAP and REST

Before you spend hours fretting over the choice between SOAP and REST, consider that some Web services support one and some the other. Unless you plan to create your own Web service, the decision of which protocol to use may already be made for you. Extremely few Web services, such as Amazon, support both. The focus of your decision often centers on which Web service best meets your needs, rather than which protocol to use.

SOAP is definitely the heavyweight choice for Web service access. It provides the following advantages when compared to REST:

• Language, platform, and transport independent (REST requires use of HTTP)
• Works well in distributed enterprise environments (REST assumes direct point-to-point communication)
• Standardized
• Provides significant pre-build extensibility in the form of the WS* standards
• Built-in error handling
• Automation when used with certain language products

REST is easier to use for the most part and is more flexible. It has the following advantages when compared to SOAP:

• No expensive tools require to interact with the Web service
• Smaller learning curve
• Efficient (SOAP uses XML for all messages, REST can use smaller message formats)
• Fast (no extensive processing required)
• Closer to other Web technologies in design philosophy

REST	SOAP
Assumes a point-to-point communication model–not usable for distributed computing environment where message may go through one or more intermediaries	Designed to handle distributed computing environments
Minimal tooling/middleware is necessary. Only HTTP support is required	Requires significant tooling/middleware support
URL typically references the resource being accessed/deleted/updated	The content of the message typically decides the operation e.g. doc-literal services
Not reliable – HTTP DELETE can return OK status even if a resource is not deleted	Reliable
Formal description standards not in widespread use. WSDL 1.2, WADL are candidates.	Well defined mechanism for describing the interface e.g. WSDL+XSD, WS-Policy
Better suited for point-to-point or where the intermediary does not play a significant role	Well suited for intermediated services
No constraints on the payload	Payload must comply with the SOAP schema
Only the most well established standards apply e.g. HTTP, SSL. No established standards for other aspects.  DELETE and PUT methods often disabled by firewalls, leads to security complexity.	A large number of supporting standards for security, reliability, transactions.
Built-in error handling (faults)	No error handling
Tied to the HTTP transport model	Both SMTP and HTTP are valid application layer protocols used as Transport for SOAP
Less verbose	More verbose

                                                                                                              By DeepthiReddy