Scanning is a process of quick interpretation by ignoring minor words. When you scan a written document, you search very quickly for key facts. Within the context of natural language processing, the principle is the same.
Minor words include most prepositions. A scan of the sentence, "the quick brown fox jumps over the lazy dog." Will reveal "quick brown fox jumps over lazy dog." The essence of the sentence remains. It is a frequent problem to computers that humans expand their speech with superfluous words. An enquirer as a train station may wish to know at what time the next train will depart for Manchester. A straight forward enquiry would be. "When does the next train leave for Manchester?" Is it necessary to specify which train? A scan of the question might return. "When train leave for Manchester?" It does not sound very natural to a human, but it conveys the same request as the initial sentence.
Writing a computer program to respond to English sentences scanning might be used to good effect. The traditional approach, used by SQL and Data Ease, is to insist that the operator does most of the scanning. These programs may understand phrases such as: "For Customers; list records" or "modify records in inventory" Where as a human approach may be to command. "Print a list of all the records in the customers file." Or "modify every record in the inventory file."
An imaginary application might be a plain English disk operating system which instead of accepting commands like "COPY *.C A:" Would understand commands like "COPY ALL .C FILES TO DRIVE A".
The argument against computer interfaces that understand plain English has always been that the operator has to do too much typing. In the absence of reliable and cost-effective audio input devices there is little defence against this argument. Currently commands to a computer must be typed in or selected by pointing to them.