Natural Language Understanding is primarily used in text based applications and dialogue based applications.
TEXT BASED APPLICATIONS
As the name implies text based applications deal with processing of written text such as books, newspapers, manuals, reports, e-mail messages, and so on. Natural language understanding techniques are widely used in finding the required documentation on certain topics from a database of texts, extracting information from messages, articles or documents, machine translation, and summarizing texts for certain purposes. A customer, for example, may want to find news on gold prices for the last one year or a student may want to get abstracts of research papers. Language understanding systems can be employed to do these tasks.
There are alternative techniques to use in the above mentioned applications but they follow blind approaches such as matching with keywords resulting in limited efficiency. Handling complex retrieval tasks, for example, requires computation of the representation of the information which only natural language understanding techniques can achieve. And the resulting information can be used later for inference.
DIALOGUE BASED APPLICATIONS
Dialogue based applications deal with spoken language. Interacting with computers using keyboards such as chatting also comes under this category. Question-answering systems, automated customer service over telephone, tutoring systems, controlling machines using voice, and interactive problem solving systems. Getting information from a database by sending queries, making transactions in banks and interactive tutoring systems are few examples.
Dialogue systems have to face many challenges including handling of errors in signals and inter-speaker differences. Not all speech recognition systems need language understanding to a large extent. For example, a voice controlled television has to only recognize the words uttered and use them as commands to perform functions such changing channels, increasing or reducing the volume, changing the contrast, power on and off.