This is a great article from alistapart.com explaining the differences between the human visitors and the “robot” visitors that your website experiences. We talk about these things a lot in our client meetings here, so we  thought it would be a great article to share with our readers. Enjoy!

Article from: alistapart.com
by Lyle Mullican February 12, 2013

When a user interface—intended for human consumption—reflects too much of a system’s internals in its design and language, it’s likely to confuse the people who use it. But at the same time, if data doesn’t conform to a specific structure, it’s likely to confuse the machines that need to use it—so we can’t ignore system requirements, either.

People and machines parse information in fundamentally different ways. We need to find a way to balance the needs of both.
Enter the Robustness Principle

In 1980, computer scientist Jon Postel published an early specification for the Transmission Control Protocol, which remains the fundamental communication mechanism of the internet. In this spec, he gave us the Robustness Principle:

Be conservative in what you do, be liberal in what you accept from others.

Although often applied to low-level technical protocols like TCP, this golden rule of computing has broad application in the field of user experience as well.

To create a positive experience, we need to give applications a human face that’s liberal: empathetic, flexible, and tolerant of any number of actions the user might take. But for a system to be truly robust, its machine face must also take great care with the data it handles— treating user input as malicious by default, and validating the format of everything it sends to downstream systems.

Building a system that embraces these radically different sets of constraints is not easy.

At a high level, we might say that a robust web application is one that:

  1. Accepts input from users in a variety of forms, based first on the needs and preferences of humans rather than machines.
  2. Accepts responsibility for translating that human input to meet the requirements of computer systems.
  3. Defines boundaries for what input is reasonable in a given context.
  4. Provides clear feedback to the user, especially when the translated input exceeds the defined boundaries.

Whether it’s a simple form or a sophisticated application, anytime we ask users for input, their expectations are almost certainly different from the computer’s in some way. Our brains are not made of silicon. But thinking in terms of the Robustness Principle can help us bridge the gap between human and machine in a wide range of circumstances.
Numbers

Humans understand the terms “one,” “1,” and “1.00” to be roughly equivalent. They are very different to a computer, however. In most programming languages, each is a different type of data with unique characteristics. Trying to perform math on the wrong kind of data could lead to unexpected results. So if a web application needs the user to enter a number, its developers want to be sure that input meets the computer’s definition. Our users don’t care about such subtleties, but they can easily bubble up into our user interfaces.

When you buy something over the phone, the person taking your order never has to say, “Please give me your credit card number using only digits, with no spaces or dashes.” She is not confused if you pause while speaking or include a few “umms.” She knows a number when she hears one. But such prompts commonly litter web forms, instructing users to cater to the computer’s needs. Wouldn’t it be nice if the computer could cater to the person’s needs instead?

It often can, if we put the Robustness Principle to work to help our application take a variety of user input and turn it into something that meets the needs of a machine.

For example, we could do this right at the interface level by modifying fields to pre-process the user’s input, providing immediate feedback to the user about what’s happening. Consider an input field that’s looking for a currency value:
Form input requesting a currency value

HTML 5 introduces some new attributes for the input element, including a type of number and a pattern attribute, intended to give developers a way to define the expected format of information. Unfortunately, browser support for these attributes remains limited and inconsistent. But a bit of JavaScript can do the same work. For example:

The first input simply blocks any characters that are not digits or decimal points from being entered by the user. The second triggers a notification instead.

We can make these simple examples far more sophisticated, but such techniques still place the computer’s rules in the user’s way. An alternative might be to silently accept anything the user chooses to provide, and then use the same regular expressions1 to process it on the server into a decimal value. Following guideline number three, the application would perform a sanity check on the result and report an error if a user entered something incomprehensible or out of the expected range.

Our application’s liberal human face will assume that these events are the exception: If we’ve designed and labeled our interfaces well, most people will provide reasonable input most of the time. Although precisely what people enter (“$10.00” or “10”) may vary, the computer can easily process the majority of those entries to derive the decimal value it needs, whether inline or server-side. But its cautious, machine-oriented face will check that assumption before it takes any action. If the transaction is important, like when a user enters the amount of a donation, the system will need to provide clear feedback and ask for confirmation before proceeding, even if the value falls within the boundaries of normalcy. Otherwise, aggressive reduction of text to a number could result in an unexpected—and potentially very problematic—result for our user:
Overly aggressive reduction of text input to a number leads to unexpected results
Dates

To a computer, dates and times are just a special case of numbers. In UNIX-based systems, for example, time is often represented as the number of seconds that have elapsed since January 1, 1970.

For a person, however, context is key to interpreting dates. When Alice asks, “Can we meet on Thursday?” Bob can safely assume that she means the next Thursday on t