Usability

Good usability is absolutely necessary for any product´s or system´s success!

Human beings interact with various kinds of systems or services, whether it be

• a video recorder, a web based system, a software application or a ticketing machine (what?)
• for private or business purposes, on ones own decision or told to do so (why?)
• at home, on the move, at their place of work or a leisure place (where?)
• target/task oriented or browsing (what for?)
• as business person, traveler, teacher, child, scientist (who?)
• at day or night, waiting, driving or relaxing (when?)

The objective as well as the subjectively perceived quality of this interaction is commonly considered as "usability". Usability means the quality of a system from the viewpoint of using it for the user´s intentions and within the user´s context.

Which characteristics make a system easy to use? The following five criteria are the most commonly cited ones and are therefore also often used as a definition for usability:

• Learnability - A system should be easy to learn and the user should be able to carry out basic tasks after a short period of time.
• Efficiency - Once the user has learned how to use the system, he should be able to carry out tasks efficiently. For expert users, it should be possible to interact with the system even more efficiently.
• Memorability - Sporadic users should remember how to use the system without having to follow the whole learning process again.
• Reduced Error Rate - While working with a system, the user's errors have to be minimised. The system should "forgive" the user´s errors and recover from an error immediately.
• Subjective Satisfaction - The system should be pleasant to use.

These criteria have been set up approximately 10 years ago, when systems were static and mostly business task focused. By now, systems have become dynamic, flexible and "alive" and their usage is no longer limited to business or work context or technical experts. Therefore additional requirements have emerged: see user experience.

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