A huge chasm divides the application development world, one that dozens of vendors are rushing to fill. On one side are desktop applications; on the other are Web applications. In between are RIAs (rich Internet applications), which have attracted droves of developers and will continue to do so for years to come.

Desktop applications respond quickly, present complex user interfaces gracefully, and take full advantage of the resources of the local computer. On the flip side, they require an installation procedure, must be compatible with all the other locally installed software, and need to be updated, which may introduce incompatibilities.

Classic Web applications need no installation, are always up to date, and can be made universally compatible. On the other hand, they tend to be unresponsive, their user interfaces are limited, and they can be knocked for a loop by server loads and connectivity issues.

RIAs attempt to combine the strengths of desktop and Web applications without falling prey to their weaknesses. RIAs try to present most of their user interfaces at the client so that they can be responsive and the interface can be as complex as it needs to be. RIAs often do need an installation, but usually only for the runtime engine, which tends to be small and most often updates itself automatically. The RIA application itself typically launches from the remote server.

RIAs try to allocate resources to the most appropriate place. If the gating issue is the overall scalability of the application, then the designer of the RIA will run most of the CPU-intensive computations on the client. On the other hand, if the application uses a database intensively, then many actions will run on the server.

Many RIAs are written to accommodate intermittent connectivity. If such an app needs a database resource, a local database kicks in when the local computer disconnects from the Internet. When an Internet connection is reestablished, the application synchronizes the local database with the central database.

I don’t believe for a minute that RIAs are going to take over the world. There will always be applications that are best implemented on the desktop and others that are best implemented on the Web. What I believe is that RIAs will play an increasingly important role in bridging the gap between desktop and Web applications, and eventually at least one technology may come along to unify the whole spectrum. I’m not sure what that technology will be — or even whether it’s something we’ve already seen or has yet to be created. But I expect for it to emerge in the next five years.

The term “Smart Client” is meant to refer to simultaneously capturing the benefits of a “thin client” (zero-install, auto-update) and a “fat client” (high performance, high productivity, Feature Rich).

RIAs typically do the following:
* run in a web browser, or do not require software installation
* run locally in a secure environment called a sandbox

Web applications are popular due to the ubiquity of a client, sometimes called a thin client. The ability to update and maintain web applications without distributing and installing software on potentially thousands of client computers is a key reason for their popularity. Common web applications include webmail, online retail sales, online auctions, wikis, massively multiplayer online role-playing games and many other functions.

There is a paradigm shift underway. In this shift, developers are creating user interfaces which more closely model the natural world. Since 2002, the term used to describe these types of software applications is “Rich Internet Applications”, or RIAs. Technologies like Ajax, Flex, Silverlight, Adobe AIR, and JavaFX are growing in popularity as this shift to RIAs gains momentum.

But what is an RIA? Answering that question is like trying to answer “What is a tree?” You may be able to identify an RIA or a tree with certainty when you see one, but coming up with an exact definition can be very difficult. In cases like this, the best one can do is to identify some of the fundamental characteristics that the term encompasses.
When you break down the phrase “Rich Internet Applications”, you find that “Internet” and “Applications” are well understood. It’s the “Rich” aspect that makes RIAs interesting, and it’s the “Rich” aspect that requires a fuller explanation. Essentially, a Rich Internet Application is capable of delivering a rich experience to the user. It is the richness of the experience that is often enhanced by making software that is more natural – more connected, more alive, more interactive, and more responsive.

Connected
We are all connected. On this relatively small planet we all have many things in common. We communicate with one another via many different methods, in many different languages, sometimes easily and sometimes with difficulty. Likewise RIAs are built on a network that connects us all - the Internet. RIAs use this network of billions of connected pieces to help us communicate - between each other and between systems, sometimes easily and sometimes with difficulty. And like each of us, in some scenarios RIAs need to be able to work when disconnected from the Internet.

Alive
Movement and the passing of time are critical to our experience of beauty and the emotional reaction we have to it. Watching waves continuously crash on a beach is an experience which fills us with life. Similarly, we would not sit and watch a beautiful sunset for very long if it never changed. In RIAs, we create rich experiences by modeling the movement and beauty we find in the natural world. Smooth sliding transitions, zoom effects, soft blurs, drop shadows, and rounded corners are elements of RIAs which help make software feel more like the natural world. Beauty is often simple and never overdone. Software that feels more alive evokes an emotional response from us. That emotional response can help to improve our overall satisfaction with the software. RIAs should feel alive.

Interactive
When people communicate they interact — sometimes physically, sometimes audibly, and sometimes visually. Interaction is how we transmit and receive information. The richness of an experience is heavily dependent on this interaction made possible by our senses. RIAs facilitate physical, audible, and visual interaction. Many new devices are allowing for more natural methods of physical interaction. Multi-touch interfaces like tablet PCs and media players are becoming more common because users want to interact with software like they interact with objects in the natural world. Many more software applications are also adding video and audio capabilities, and some of these applications support bi-directional multimedia interaction. This allows users to interact visually and audibly in the context of an application. Imagine filling out a form online and, if needed, being able to interact via webcams with someone who can help you complete the form. Applications which embrace interactivity to that level are helping to bring natural world interactivity to software experiences.

Responsive
In the real world when people interact with each other or with objects like rocks and trees, those things typically respond quickly. If I kick a rock it immediately moves, unless it’s a big rock in which case my foot immediately hurts. If someone speaks to another person they expect a timely response. At a baseball game, you can see scores whenever you want, just by looking in the right place. Too often in the world of software people are forced to wait for their computers to respond. Whether due to network connectivity issues, processing limitations, or other problems, software too often makes us wait. Most web applications leave users waiting for at least four seconds every time the user clicks on something. With many applications the wait times can be significantly longer, even on a broadband connection. Imagine what an everyday conversation would be like with that latency. Real-time streaming, high performance client side virtual machines, and local caching mechanisms are becoming in integral part of RIAs because these technologies reduce latency, increase responsiveness, and make software feel more like the natural world.

Natural Software Experiences
All kinds of software applications — from ERP business applications to word processing applications — are embracing the characteristics of what we now call Rich Internet Applications. This move is happening because users intuitively want to experience software like they experience the natural world.

Rich Internet Applications are proliferating because they are more connected, alive, interactive, and responsive than yesterday’s software. In ten years nearly all software will be what today is called a Rich Internet Application. But in ten years it will be only natural to just call it “software”.

On one hand, an RIA takes advantage of a connection - an internet connection, a connection to data. The fact that the application is on the internet is not enough. A great RIA leverages its connection to provide value. Being connected to a network adds a layer of possibilities that traditional applications do not have.

The most obvious is ubiquitous distribution - the data is important, the hardware you use to access it is incidental. Great RIAs will even change their interface and features depending on how you access them. An application should provide value through many different touchpoints.

The real magic happens when these applications take advantage of their connection to the internet to enhance features. Connected applications involve collaboration and communication. Easy access to an endless range of data allows applications to connect data types together ways that foster entirely new views of information.

The second great form of connection is connecting with the user. A great RIA connects a valuable service to it’s user in a way that is memorable and entertaining. An RIA takes cues from a very wide range of disciplines: psychology, human factors engineering, consumer behavior, graphic design, storytelling. All of these varied disciplines come together in the interface to immerse and involve a user.

Applications traditionally exist to solve a problem; provide a service. Rich internet applications strive to provide this service with a healthy does of fun and wonder.

An application should start out feeling like play and then reveal it’s depth and value and finally end up feeling like a cherished and trusted tool. The “Rich” part of Rich Internet Application forges this connection.

What is the defining characteristic of a RIA?
Rich User Experience:
I think the most defining characteristic of a “Rich Internet Application” is a rich user experience. This does not necessarily mean a slick interface, or asynchronous data transfer, a stateful client interface, or any specific technology. While these may be common characteristics of RIAs, they do not define them. It boils down to how the application is used, and what it is being used for. A Rich Internet Application provides a great experience for its users. It should be easy to use, engaging, and targeted to perform its task very well. To many this means a “desktop-application-like-experience” delivered through the web. This may include common features such as drag-and-drop data manipulation and imaging/drawing/charting capabilities, but it is not a requirement to include any of these.

What are common characteristics of a Rich Internet Application?
As I mentioned above, the only real requirement of a RIA is the rich user experience. However, the richness of experience can be achieved through many common techniques:

Stateful Client and Asynchronous Data Transfer
Although not a requirement of RIA, it is very common that Rich Internet Applications employ stateful clients and asynchronous data transfer to achieve their tasks. A stateful client interface is exactly as the name describes; it maintains state of the application completely on the client side. It does not rely on the server to maintain information about what the current user is doing. This enables the ability to simplify backend logic to be more service oriented and asynchronous. The back-end services can perform specific actions or logic based on parameters passed into them, regardless of who invoked them. The user interface also does not need to wait on the backend logic.

Asynchronous data services are performed behind the scenes, while the user interface is still accessible to the user. The user may not even know that a remote service method has been invoked. This enables the user to keep using the application seamlessly, which helps lend to the desktop-application feeling.

Additionally, asynchronous data services typically only contain data, no UI declarations; it is up to the stateful client to determine how the data will be displayed. This typically reduces the size of the requests back and forth to the server, and often results in reduced server load and better interface responsiveness. Not to mention, the client application does not loose its place when the service request has been made. The user can keep working with the application, and can show active feedback to the user, such as a loading animation while the service request is being executed.

Drag-and-Drop UI Paradigm
Also not a requirement, but a common paradigm implemented within Rich Internet Applications is “drag-and-drop”. Ask anyone, especially non-technical people, what is easier: typing into a bunch of forms to enter information, or dragging an item onto a “cart” and having the information automatically populate? The answer is clearly drag-and-drop. This technique varies based on the technology implementations and restrictions, but its benefits can been seen clearly. Dragging items onto online maps, dragging commercial goods into shopping carts, creating “drag-able” objects in online office productivity applications, and even “drag-able” elements in online image editing applications are all rich features that are capable because of the drag and drop paradigm. This type of capability didn’t exist in mainstream online applications until the “RIA Revolution”. Now you see it everywhere.

Drawing and Analytical Tools
Not every application has these either, but they really add a lot when they are used properly. Many RIA technologies enable the capability to manipulate graphics onscreen at runtime. This enables charting and complex data visualizations, and in some cases, even 3D modeling. An image is worth a thousand words, and these types of capabilities enable your application to say a lot. Without the bloat of large tables of data that the user has to analyze in order to see the trends; the user can simply look at it, and instantly see what is going on.

What technologies are used to create Rich Internet Application?
Lots of them - there is no single technology that is best suited for RIA. There are lots of great technologies that enable various capabilities. The choice of technology should be determined based upon your needs, and your application users’ needs. Typically I prefer Adobe Flex on the front end because it makes a lot of these paradigms easier, and enables rapid development cycles, but there are many options:

* AdobeFlex
* AJAX (there are many AJAX frameworks available)
* Microsoft Silverlight
* Java FX
etc…

I know I didn’t name every option, but the truth of the matter is that you have an option. There is no definitive “right choice” for all occasions. The desired capability and features of your application, in conjunction with your available development resources, technical requirements, and current infrastructure should determine which technology suits your needs most adequately.

On the back end, there is not any requirement for RIA. You are not limited to any specific application server or language. I have personally worked on RIAs that employ ColdFusion, Java/J2EE, .NET, and PHP, and I know that there are numerous other options out there. As with your client-side interface technology, your backend technology should be determined by the needs of your application, your resources, and your infrastructure. Are you serving dynamic data? Are you streaming media? Are you employing real-time messaging? Are you upgrading an existing system, or building one from the ground up? Does your organization support open source initiatives? Does your organization prefer commercial products that have technical support? What is your budget for technology? There are many variables in the equation, and many solutions to the problem. RIA is not locked in to any one specific technology, nor do I expect it to ever be.

Is Web 2.0 RIA?
No! Web 2.0 is a marketing buzzword. I truly believe that “Web 2.0″ originally meant the same thing as RIA, however it has been completely overused and abused. Web 2.0 has been degraded to a reference for common graphic design elements such as rounded corners, gradients, transparencies, and reflections. I don’t doubt that the term RIA will also become overused and abused, but the ideas behind RIA will not. It all boils down to the application, the user experience, and the ability to for the application to perform its task well.

Is RIA always the right choice?
The choice of RIA depends on the context. In many cases, yes it is the right choice. In many cases, it is not. RIA is best suited for applications, not web sites. There is a definite distinction there.

I think a limited amount of RIA concepts, such as asynchronous lookups for text boxes can be helpful in a web site, however too much could potentially kill the web site and make it difficult to use. RIA is great for office productivity applications, business/data analysis applications, media applications, graphics applications, and online mapping, but it does not suit every need and every purpose.

Many RIA technologies cause sites to have problems being indexed by search engines. RIA technologies must be designed with search engine optimization in mind for them to work properly with search engines.

When employed properly, applications benefit from RIA principles and technology. As with any technology, RIA methodologies can be overused and abused, and it is up to the discretion of the developers and providers to implement them correctly. The developer/provider company *should* know their users/customer/consumers best.

“RIA is an application that runs in the traditional browser but utilizes an intermediate layer that can bypass the traditional Page Refresh that has been a standard of most current web applications. The most common tools that can achieve this intermediate layer include JavaScript used in Asynchronous JavaScript and XML (Ajax) applications, as well as Flex or Flash using the Flash Player. Other RIA solutions include OpenLaszlo (which utilizes the Flash Player as well as Ajax), XUL (which is dependent on a Mozilla-compatible browser), JavaFX from Sun, and the Microsoft Silverlight.”

My non technical opinion on RIA is that a well designed RIA can be a truly engaging experience to the user. It will allow the user to flow to many areas of the application without feeling the agony of click and wait which was the norm when browsing the internet since its inception. RIA can also seamlessly include multimedia (audio, video, screencasts, etc) , 3rd party tools (maps, messengers) to enhance the users experience. There is an obvious danger of doing these things because you can rather than because you should so as difficult as it is for a developer like myself to say, user experience designers are the key to building RIA that really shine. Time spent doing research on how to build the user experience you are trying to obtain will not be time wasted.