Usability is a necessary condition for survival. If an application is difficult to use, not interesting or not looks good, people will never use it again. In order to offer good quality applications to Tizen Store users, good usability is required as well as other software quality related requirements. Tizen Validation team regard that developer’s success is closely related with customer’s satisfaction. So, based on international consensus standard, we defined application usability as overall satisfaction on application usage. It covers interest, reliability (performance), easy to use, enough features to achieve goals and application design.

There are 5 main criteria to measure usability in a quantitative manner.

1. Interest/Usefulness

   Definition	Level of interest or usefulness delivering to user. The main purpose of this standard is to measure how much users would want the applications and how frequently would be used.
   Questionnaries	- Does it have interesting contents or level that user expected? - Does it help user be more effective? - Does it give users more control over the activities in their life? - Does it make the things that user wants to accomplish easier to get done? - Does it meet user’s needs? - Would occasional and regular users like it?

2. Reliability(Performance)
   

   Definition	How fast and less errors while using application.
   Questionnaries	- Is there any critical problems? (crash / force quitting) - Is there any major problems? (main feature doesn’t work, it returns wrong result) - Is it a few possibilities to occur problems? - Is it available to enjoy in a fast manner? - Does it handle exception cases? - Is loading time is fast? (within 10 sec according to the validation guide) - Is it easy to recover from mistake or wrong input?

3. Easy to use
   

   Definition	How easy to learn and use the application.
   Questionnaries	- Is it simple to use? - Is it user friendly? - Does it require the fewest steps possible to accomplish what user wants to do with it?(Navigation convenience) - Is it available with less effort? - Is it available to use without written instructions? - Are there any inconsistencies while using it? - Is it available to use successfully every time?

4. Enough features
   

   Definition	Whether or not to provide enough valuable features to users
   Questionnaries	- Is it available to do any task as user intended? - Does it provide any additional valuable features? - Does it do something user would expect it to do? - Does it help user be more productive with valuable features?

5. Application Design
   

   Definition	How beautiful the application UI is and how well arranged objects (button, combo box, etc.) in each page.
   Questionnaries	- Are the objects arranged harmoniously? - Are the colors in applications matched well? - Does application provide good quality iconographic or infographic? - Does application provide good quality images or graphics? - Are the texts easy to read? (too small or too large size of text make readability low) - Is not there any resolution issue?