Definition:

Accessibility is one of the major tenets of design, and covers almost every design practice. Accessibility is not just whether or not someone with a disability can use a design effectively. It also covers the ability of a design to have mutual benefits for diverse groups of users. Can both a new user and an advanced user both accomplish their own specific goals?

Interaction Design:

In interaction design accessibility focuses on two very different types of design problems — human needs and technical limitations. It is a well known principle of accessibility to account for color-blindness, users with poor eyesight and other physical disabilities. Technical limitations due to aging browsers, lack of Javascript and slow internet connections are starting to become just as important within web application accessibility. Flickr's sign up button has a few issues with color blindness — doesn't the button on the right look disabled?

User Experience Design:

In user experience design, accessibility also contains a human element and a technical element. The Rackspace Cloud's current signup process requires a phone-based fraud check. What if our new user is completely legitimate but can't speak any of the languages that Rackspace representatives do? Can a 6'8" man realistically fit into his new Porche? The accessibility of a Porche's cockpit is a technical limitation that was designed to balance mechanical systems, aerodynamics, and the experience of driving the car. At some point, the there is a limit for each of the variables, and a decision was made to limit the physical size to increase the overall experience.

Definition:

The Aesthetic-Usability effect is the perception that more aesthetically pleasing interfaces are easier to use than less aesthetically pleasing ones. "Pretty" or "sexy" interfaces are also more likely to be used regardless of if they actually are easier to use.

Interaction Design:

Contemporary interaction models crafted by companies like Apple, BMW and Bank of America are prime examples of this practice. Studies have shown that users may create more errors on an iPhone than a Blackberry, but users will overwhelmingly agree that the iPhone was much easier to use. Rackspace's new Unbounded List widget is much more aesthetically pleasing than its previous version, two <select> boxes, and hopefully our users will find is more usable because of its improved look and interaction methodology.

User Experience Design:

Bank of America's new envelope-free deposits on their ATM's are actually slower than their previous counterparts because (I'm guessing here) the machine now has to count cash as it is deposited instead of accepting any envelope and having it hand-checked later. This process may be 10 seconds slower, but it seems more usable because you don't have to fight to insert cash inside an envelope and sealing it while it's 20 degrees outside.

Definition:

The 80/20 rule states that 80% of the effects generated by a system are centered around 20% of the variables in the system. Design teams can use this rule to their advantage by focusing the bulk of their efforts on the 20%. The rest of the system shouldn't be neglected, but a janitor's closet doesn't need to be as well designed as the stadium seats.

Interaction Design:

In interaction design, this most commonly refers to the two or three most trafficked pages, such as the Facebook news feed or a Google search listing. Within Rackspace's Cloud Apps, the Control Panel mailbox listing is our most commonly accessed page and the design team's focus should reflect that.

User Experience Design:

In user experience design, this rule is represented in common experiences that most customers must do — checking out at the grocery store, syncing an iPhone/iPod or filling up your car at a gas pump. Think about your last experience with a self-checkout kiosk at a grocery store. Did you leave with a smile on your face? Were you delighted? Half-assed efforts are causing severe damage to the UX of buying groceries and shows just how damaging this rule can be.

As a design moves between product owners, business analysts, product managers and developers, small design decisions and functional specs get lost for many reasons — requirements change, revisions are made and parties aren't always represented correctly. Sometime's a developer is under time constraints and must improvise. This isn't a bad thing, it happens at Rackspace, Google, Facebook and other large companies all the time.

This phenomenon can't and shouldn't be stopped. Instead, I want to educate developers; to teach what is important and how to improvise by learning basic design principles. To some, insignificant details like error message wording or whether an action is triggered with a link or an HTML button isn't important, but it really is — and I want to teach you why.

Follow along via Twitter or RSS over the next few weeks for a new design principle every day. Here's a preview of the first few topics:

• Lesson 1: The 80/20 Rule
• Lesson 2: Aesthetic-Usability Effect
• Lesson 3: Accessibility
• Lesson 4: Affordance
• Lesson 5: Consistency