"Application" and "OK"

"Application" and "OK" are two frequently used button commands in the software. However, during daily development, I found that not everyone knows the difference between the two commands, what to do during "application" and "OK" is not clearly handled.
1. When should the "application" button appear?
A simple principle is that if an interface only processes one transaction at a time, the "application" button should not appear, such as a simple user confirmation. On the contrary, if the interface may need to process multiple transactions at the same time, the "Apply" button command should usually appear.
2. Differences between "application" and "OK"
Since the "application" button appears only in Multi-transaction processing, the "application" is used to persist or save the currently processed transactions, for example, if the options window of IE is a dialog box with multiple pages, you can use "application" to save the processing of each page, however, the "OK" button command is used to process all the transactions in the dialog box, and the current window is closed after being saved, and the button command is not used to close the window.
If the window processes simple information, such as database operations, the situation may be simpler. However, if database operations are involved, you must perform a logical check on the database during application and determination, it is possible that the keyword may be modified during the application. If you want to modify the keyword, the key value will be duplicated.
Another possible scenario is that, for batch data input, the application simply records user data, such as adding data to an arraylist, then, save the data when you confirm it. The difference between the two is obvious. At this time, an additional role of the Application Command is to reset the user input window.