multi-tap
multi-tap又称 multi-press .
是在手机，或者电视遥控上的keypad定义，有如下2类标准:
1. ITU-T E.161
2.T9
使用举例如下：
Consider a typical phone keypad:
A standard ITU-T E.161 keypad used for text messaging
Suppose a user wishes to type the. In a traditional "multi-tap" keypad entry system, it would be necessary to do the following:
Press 8 (tuv) once to select t.
Press 4 (ghi) twice to select h.
Press 3 (def) twice to select e.
Meanwhile, in a phone with predictive text, it is only necessary to:
Press 8 once to select the (tuv) group for the first character.
Press 4 once to select the (ghi) group for the second character.
Press 3 once to select the (def) group for the third character.
The system updates the display as each keypress is entered to show the most probable entry. In this case, predictive text reduced the number of button presses from 5 to 3. The effect is even greater with longer words and those composed of letters indicated towards the far end of each key.
A dictionary-based predictive system is based on hope that the desired word is in the dictionary. That hope may be misplaced if the word differs in any way from common usage—in particular, if the word is not spelled or typed correctly, is slang, or is a proper noun. In these cases, some other mechanism must be used to enter the word. Furthermore, the simple dictionary approach fails with agglutinative languages, where a single word does not necessarily represent a single semantic entity.
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