On the other hand, poor usability means that people using your web site cannot efficiently perform the tasks you intended. 

Poor usability can come from overly complex web sites, can lead to large numbers of user errors, or can mean that people just don’t like using your system. 

For instance, one aspect of usability is that users should know what to do next.  They should either be given explicit instructions or the web site should follow some known interaction pattern. 

If the next steps are not obvious, users will spend precious time trying to figure them out.  They may make mistakes or may just leave your web site with a bad feeling.

WHAT IS USABILITY?
Usability is defined as the degree to which people/users can perform a set of required tasks. It is the product of several, sometimes conflicting design goals:

- Functionally correct:  The primary criterion for usability is that the system correctly performs the functions that the user needs.  Software that does not allow users to perform their tasks is not usable.

- Efficient to use:  Efficiency can be a measure of the time or actions required to perform a tasks. In general, procedures that are faster tend to be more efficient.

- Easy to learn:  Ease of learning determines how quickly new users can learn to accurately perform a task procedure. In general, the fewer steps a procedure contains, the easier it is to learn.

- Easy to remember.  The degree to which a system taxes human memory determines how easy it is users to remember. 

Systems that compel users to paste memory aids on their display screens are not easy to remember.

- Error tolerant:  Error tolerance is determined by how well errors are prevented, how easily they are detected and identified when they occur, and how easily they are corrected once they are identified. 

Error tolerant systems can also prevent catastrophic results if all other measures fail.

- Subjectively pleasing:  In the end, usability is often determined by how users feel about using the system. 

Although nonfunctional graphics and other interface elements can skew a user’s perception of usability, user satisfaction is probably a combination of all these criteria.

Because the goals of usability can conflict with one another, the context of the design will determine the priority with which each goal is applied. 

For instance, a kiosk system that assumes no prior training would probably have ease of learning a primary usability goal. 

A safety-critical system, such as a nuclear power plant, would have error tolerance its primary usability goal. 

On the other hand, a video game would have to be fun to use (subjectively pleasing) in order to succeed in the marketplace. 

In addition, video game designers often depend on human error to make their designs more compelling, so conditions for human error are purposely built into games.

Only by attending to the myriad details does usability emerge a dominant property.  To ensure high usability on our own web projects, we defined a development process that incorporates proven techniques from software and usability engineering, graphic design, project management, and other disciplines. 

The process had to be practical and lean.  It had to allow us to work on multiple projects of varying sizes with fixed budgets. 

It had to help us keep track of the details that can kill usability and destroy profitability.  This book is about that process.

WHY IS USABILITY IMPORTANT FOR WEB SITES?
Web browsers have become a de facto standard for interbusiness communication and commerce in the new e-business paradigm. 

We are in the midst of a massive shift from diverse technology structures with business organizations, to a model in which business units have access to the most up-to-date information available, data is only entered once, and changes propagate instantly.

Legacy information systems have been given new life as businesses use the Web to provide stored corporate knowledge to those who need it, both inside and outside an organization. 

Web-based applications have become a standard, cross-platform nonproprietary means for businesses to communicate with each other and with consumers.

Businesses are continuing to increase their productivity, with information technology playing a critical role. 

Increased productivity is belonging an necessary element for achieving or retaining a competitive edge.  It may even be the key to survival for some businesses. 

Nevertheless, we have seen in the past that technology alone cannot achieve increased productivity. 

Actuality, there is ample evidence that technology can decrease productivity if poorly applied. 

High usability is a key factor in achieving maximum return on information technology investments.

WEB USABILITY PROBLEMS
Although the Web is based on a relatively simple interface consisting of links, buttons, menus, text fields, text, and graphics, sever usability problems are common. 

The four broad areas that contribute to these problems:  human perception, navigation, human memory, and database integration. 

We will discuss these areas in detail and provide examples for the types of usability problems they can include.  While there are certainly other areas that can be troublesome, this discussion should provide a convincing argument for, integrating usability into web design.

Human Perception Problems
Perceptual issues can occur when pages are designed according to how the underlying information is physically stored (e.g., in a database), rather than how the information can best meet the needs of the user. 

This strategy may make page delivery and maintenance efficient, but it can also make the user’s task slow and error prone. Other perceptual problems can arise when artistic style is considered before usability. 

Navigation
Navigation disorientation is among the biggest frustrations for web users.  Three common questions users ask themselves while navigating on the Web are:

Where am I now?
How do I get where I want to go? and
Where does this go?
 
To find a navigation path, users must predict what will happen if a particular link is pressed and determine whether it takes them closer to their goal.

Navigation design issues include whether there is a logical architecture to the information in a site, whether there are sufficient indicators to give the user’s current location, and whether the language and the organization of the navigation system match the user’s expectations and needs for the task.

One navigation problem comes from the use of ambiguous links that may cause the user to go to the wrong page. 

Human Memory
There are three primary human memory issues to consider when designing for the Web.  First, if too many items must be remembered, it is likely that something will be forgotten. 

Second, the longer the time frame that items must be remembered, the more likely they are to be forgotten. 

Third, the greater the similarity among the remembered items, the more likely they are to be confused with one another. 

Web sites that required users to remember items from one page to the next are likely to cause problems.

Database Integration
As Web technology has matured, database systems have become a central tool for building web-based software applications. 

Although this approach is very powerful and can easily streamline ongoing system maintenance, issues with integrating database technologies can create severe usability problems for the end user. 

A common problem is that information that the user sees gets out of sync with information in the serving database. 

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