Welcome!

Java Authors: Carmen Gonzalez, Liz Dickinson, Pat Romanski, Bob Gourley, Yakov Fain

Related Topics: SOA & WOA, Java

SOA & WOA: Article

The Right End of REST

REST is all about distributed hypermedia applications. They’re the point of REST.

One of our Licensed ZapThink Architects, Michael Poulin, struggled with our recent ZapFlash, Where is the SOA in REST-Based SOA? In a forum post, Poulin asked:

If we have a UI that works with the middle- and back-end resources, do we care if … REST or Web Services are used behind the UI? If [the] UI all of a sudden becomes the orchestrator on its own (which contradicts the essence of Service with interfaces where one of [them is the] UI), how [may the] UI journey/workflow … be attributed to the communication channels - REST calls - running behind it? What constitute[s] “A REST application” … and how [does it differ] from non-REST application[s], especially from the architecture perspective? Where [is] the Architecture and where [is] the architecture Implementation?

Poulin is not alone in his confusion. The topic of REST is a minefield: it seems that most people don't understand it, even when they write authoritatively on the subject. And the true authoritative source, Dr. Roy Fielding, speaks in the precise yet obscure prose of an academic, often sowing as much confusion as he does clarity. And yet, the answers lie in Fielding's explanations, even though studying them feels a bit like sitting at the feet of the Buddha, hoping for enlightenment.

Unraveling REST
Let's begin with Wikipedia, a source Fielding bemoans as being a poor substitute for truth. Be that as it may, it's an expedient starting point. Wikipedia defines REST as "a style of software architecture for distributed hypermedia systems such as the World Wide Web." I always thought this definition was rather silly: after all, how many distributed hypermedia systems can you think of other than the Web? But in fact, this definition leads us to the answers to both of Poulin's core questions: first, what constitutes a REST application, and second, where is the architecture and where is its implementation?

Of course, Fielding's precise definition of REST differs from the Wikipedia simplification. According to Fielding, "the Representational State Transfer (REST) style is an abstraction of the architectural elements within a distributed hypermedia system." And therein lies the key to Poulin's second question: REST is an abstraction.

Of course, abstractions are nothing new-they are the basic tool of any architect, and a topic ZapThink has spoken about numerous times. But most people don't quite grok just how abstract REST is. For example, do you think that REST is HTTP-specific? No, it's not. It deals with abstracted hypertext protocols, of which HTTP is the most familiar. Does REST call for uniform interfaces consisting of GET, POST, PUT, and DELETE operations? No again. Those are examples of uniform interface operations, but REST itself doesn't specify them, other than an abstracted GET operation. And of course, resources are abstractions of server capabilities or entities, not the capabilities or entities themselves, while representations are abstractions of media type instances, not the instances themselves. Even the terms "client" and "server" are abstractions: a REST client may actually run on a physical server, and a REST server may serve as a client. In fact, there's nothing "client/server" about REST.

So when Wikipedia uses the phrase "a style of software architecture for distributed hypermedia systems such as the World Wide Web," it's pointing out that REST applies constraints to abstracted distributed hypermedia systems, of which the Web is only the most familiar example.

Confused yet? You're not alone, and that's the point. Architects look at the level of abstraction behind REST and wonder, "how can this mess be useful?" while developers look at it and think, "OK whatever, let's build a RESTful API and go from there." At that point, the architects take off their architect hats and dive into the technical details alongside the coders. The result? A lot of noise and confusion, ostensible RESTful APIs that are not really RESTful at all, and the mistaken belief that you can comply with some of the REST architectural constraints but not all of them, and still be doing some kind of REST.

And that brings us to Poulin's first question: what is a REST application anyway?

REST Applications: More than Bricks & Mortar
A REST application is a distributed hypermedia application, of course - something you apply a distributed hypermedia system to in order to accomplish some goal. Easy to say, but deceptively difficult to understand, until you realize that REST is all about distributed hypermedia applications. They're the point of REST. If you think you're "doing" REST without the goal of building a distributed hypermedia application, you're missing the point of REST entirely.

Unfortunately, most people who are trying to do REST, simply put, are missing the point of REST entirely!

It's as though we're trying to build a brick building, so we hire an architect who comes up with plans for a brick building. But we look at the plans and we don't really understand them, but we know we want to build with bricks, so we spend all our time figuring out the best way to mix mortar. Once we've come up with really good mortar, we convince ourselves we know how to build the building, even though we still don't understand the plan.

That's the state of REST today. People look at REST's four architectural constraints, and say, hmm, I don't understand the fourth one - Hypermedia as the Engine of Application State (HATEOAS). But I think I can figure out the bits about resources and representations. What they're failing to realize is the hypermedia bit is the point of what they're doing, just as actually building the building according to plan is the point of the mortar.

The mortar-first approach to REST has been institutionalized in the form of the Richardson Maturity Model, which suggests that HATEOAS is at the highest level of maturity, and it's perfectly fine to start at the lower levels and work your way up. In other words, it's fine to start construction once you have good mortar; you'll figure out the plan eventually. Clearly, that's no way to build a house!

The Right End of REST
What is it about HATEOAS that's so difficult? State engines? Computer Science 101, puhleeze. Hypermedia? Not really that confusing, either. After all, hypertext is just a document with links in it to other documents, and by generalizing hypertext to the term hypermedia, we're simply allowing for media other than HTML documents and the like. After all, a video or sound file could have a link in it, right? So, where's the confusion?

The confusion lies in the second letter A - application. As in distributed hypermedia application. The point of REST, remember? The architectural starting point for any implementation that REST constraints are appropriate for is the design of the hypermedia application that meets the given business requirements. If you look at the business requirements, and your expertise as an architect tells you that a distributed hypermedia application isn't the right thing to build, then don't use REST.

On the other hand, a distributed hypermedia application might be just the ticket. The next question you should ask is: how dynamic should this application be? In other words, what agility does the business require? Put the analysis that provides the answer to that question in your Agility Model. Then let the Agility Model - not the Richardson Maturity Model - guide your design.

RESTful Agility Levels
To illustrate the agility levels for distributed hypermedia applications that should frame your Agility Model, let's work through some concrete examples. As you go through these levels, compare them to the Richardson model.

Level 1: Static hypermedia application, consisting of a set of static Web pages containing nothing but HTML, interconnected by links. Not particularly agile. Is it REST? Yes, but in a very simplistic way. Does it meet your requirements? Probably not. (Level 1 is good enough for our ZapFlashes, however, in case you hadn't noticed.)

Level 2: Hypermedia application consisting of static Web pages that contain HTML and client-side JavaScript (no funky Ajax or the like). Pages link to each other, and the links may be dynamic, based upon client-side logic in the JavaScript.

Level 3: Hypermedia application consisting of dynamic Web pages built on the fly on the Web server, using php or Java Server Pages or whatever server scripting environment floats your boat. Pages link to each other, but the links may be dynamic, based upon server-side logic.

Level 4: Hypermedia application consisting of a set of dynamic representations that conform to a variety of media types (HTML documents, XML documents, images, video, you name it), where those representations have links to other representations, and furthermore, the links may be dynamic, based upon client-side or server-side logic or both, as appropriate.

Once you have determined the agility requirements for your application, now you may think about how best to implement its components - the hyperlinked representations. Answering that question finally leads you to a consideration of the resources that generate those representations. But you don't start with the resources, you start with the hypermedia application. You finish with the resources.

The ZapThink Take
The examples in the agility levels above are just that: examples. Particular implementation decisions that may be appropriate for a given situation. The architecture, however, is the overall, best practice-driven approach for beginning with the business challenge and working through the levels of abstraction to come up with a working implementation at the end. As an architectural style, REST is simply a set of constraints on the architecture: one way of doing things that makes it easier to solve certain problems. The architect must decide whether REST or any other style is appropriate for the problem at hand, but if you choose REST, then you must begin with the distributed hypermedia application you wish to build.

Hopefully I've answered Poulin's questions (I'm sure he'll let us know if I haven't). But there's still a part of his post left to address. If you read to the end, you'll see he wonders what happened to ZapThink. Well, Michael, we're a part of a larger company now, to be sure, but I'm still here, and I continue to do my best to push the envelope of architectural understanding. That's why we continue to update our Licensed ZapThink Architect course, which is now at version 9, and includes expanded content on REST-Based SOA, as you might expect. We hope to see you in a future class - and if you're in the Washington DC area, please come to our ZapForum networking event on October 12th and meet the "new" ZapThink. RSVP to [email protected] if you'd like to join us!

More Stories By Jason Bloomberg

Jason Bloomberg is the leading expert on architecting agility for the enterprise. As president of Intellyx, Mr. Bloomberg brings his years of thought leadership in the areas of Cloud Computing, Enterprise Architecture, and Service-Oriented Architecture to a global clientele of business executives, architects, software vendors, and Cloud service providers looking to achieve technology-enabled business agility across their organizations and for their customers. His latest book, The Agile Architecture Revolution (John Wiley & Sons, 2013), sets the stage for Mr. Bloomberg’s groundbreaking Agile Architecture vision.

Mr. Bloomberg is perhaps best known for his twelve years at ZapThink, where he created and delivered the Licensed ZapThink Architect (LZA) SOA course and associated credential, certifying over 1,700 professionals worldwide. He is one of the original Managing Partners of ZapThink LLC, the leading SOA advisory and analysis firm, which was acquired by Dovel Technologies in 2011. He now runs the successor to the LZA program, the Bloomberg Agile Architecture Course, around the world.

Mr. Bloomberg is a frequent conference speaker and prolific writer. He has published over 500 articles, spoken at over 300 conferences, Webinars, and other events, and has been quoted in the press over 1,400 times as the leading expert on agile approaches to architecture in the enterprise.

Mr. Bloomberg’s previous book, Service Orient or Be Doomed! How Service Orientation Will Change Your Business (John Wiley & Sons, 2006, coauthored with Ron Schmelzer), is recognized as the leading business book on Service Orientation. He also co-authored the books XML and Web Services Unleashed (SAMS Publishing, 2002), and Web Page Scripting Techniques (Hayden Books, 1996).

Prior to ZapThink, Mr. Bloomberg built a diverse background in eBusiness technology management and industry analysis, including serving as a senior analyst in IDC’s eBusiness Advisory group, as well as holding eBusiness management positions at USWeb/CKS (later marchFIRST) and WaveBend Solutions (now Hitachi Consulting).

@ThingsExpo Stories
SYS-CON Events announced today that SOA Software, an API management leader, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. SOA Software is a leading provider of API Management and SOA Governance products that equip business to deliver APIs and SOA together to drive their company to meet its business strategy quickly and effectively. SOA Software’s technology helps businesses to accelerate their digital channels with APIs, drive partner adoption, monetize their assets, and achieve a...
SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.
SYS-CON Events announced today that AgilePoint, the leading provider of Microsoft-centric Business Process Management software, will exhibit at SYS-CON's 2nd International @ThingsExpo which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. AgilePoint is the leading provider of Microsoft-based Business Process Management (BPM) software products, has 1,300+ on-premise and cloud deployments in 25+ countries and provides the same advanced BPM feature set as J2EE vendors like IBM and Appian for the Microsoft .NET native environment. AgilePoint customer...
The Internet of Things (IoT) promises to evolve the way the world does business; however, understanding how to apply it to your company can be a mystery. Most people struggle with understanding the potential business uses or tend to get caught up in the technology, resulting in solutions that fail to meet even minimum business goals. In his session at Internet of @ThingsExpo, Jesse Shiah, CEO / President / Co-Founder of AgilePoint Inc., will show what is needed to leverage the IoT to transform your business. He will discuss opportunities and challenges ahead for the IoT from a market and tec...
SYS-CON Events announced today that Utimaco will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customizable platform to easily integrate into existing software solutions, embed business logic and build s...
One of the biggest challenges when developing connected devices is identifying user value and delivering it through successful user experiences. In his session at Internet of @ThingsExpo, Mike Kuniavsky, Principal Scientist, Innovation Services at PARC, will describe an IoT-specific approach to user experience design that combines approaches from interaction design, industrial design and service design to create experiences that go beyond simple connected gadgets to create lasting, multi-device experiences grounded in people’s real needs and desires.
Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: Samsung recognizes that true, accelerated innovation cannot be driven from one source, but requires a...
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at Internet of @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, will discuss how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money! Speaker Bio: Esmeralda Swartz, CMO of MetraTech, has spent 16 years as a marketing, product management, and busin...
SYS-CON Events announced today that TeleStax, the main sponsor of Mobicents, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. TeleStax provides Open Source Communications software and services that facilitate the shift from legacy SS7 based IN networks to IP based LTE and IMS networks hosted on private (on-premise), hybrid or public clouds. TeleStax products include Restcomm, JSLEE, SMSC Gateway, USSD Gateway, SS7 Resource Adaptors, SIP Servlets, Rich Multimedia Services, Presence Services/RCS, Diame...
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, will address the big issues involving these technologies and, more important, the results they will achieve. How important are public, private, and hybrid cloud to the enterprise? How does one define Big Data? And how is the IoT tying all this together?
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic strategies that utility/cloud computing provides. Whether public, private, or in a hybrid form, clo...
SYS-CON Events announces a new pavilion on the Cloud Expo floor where WebRTC converges with the Internet of Things. Pavilion will showcase WebRTC and the Internet of Things. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices--computers, smartphones, tablets, and sensors – connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridsto...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at Internet of @ThingsExpo, Andrew Bolwell, Director of Innovation for HP’s Printing and Personal Systems Group, will discuss how key attributes of mobile technology – touch input, senso...
The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics...
Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.