The NLP system has a wide and varied lexicon to better understand the complexities of natural language. Using an algorithmic process, it determines what has been asked and uses decision trees or slot-based algorithms that go through a predefined conversation path. After it understands the question, the computer then finds the best answer and provides it in the natural language of the user.
As discussed earlier here also, each sentence is broken down into different words and each word then is used as input for the neural networks. The weighted connections are then calculated by different iterations through the training data thousands of times. Each time improving the weights to making it accurate. The trained data of neural network is a comparable algorithm more and less code. When there is a comparably small sample, where the training sentences have 200 different words and 20 classes, then that would be a matrix of 200×20. But this matrix size increases by n times more gradually and can cause a huge number of errors. In this kind of situations, processing speed should be considerably high.
Malicious chatbots are frequently used to fill chat rooms with spam and advertisements, by mimicking human behaviour and conversations or to entice people into revealing personal information, such as bank account numbers. They are commonly found on Yahoo! Messenger, Windows Live Messenger, AOL Instant Messenger and other instant messaging protocols. There has also been a published report of a chatbot used in a fake personal ad on a dating service's website.
Two trends — the exploding popularity of mobile messaging apps and advances in artificial intelligence — are coinciding to enable a new generation of tools that enable brands to communicate with customers in powerful new ways at reduced cost. Retailers and technology firms are experimenting with chatbots, powered by a combination of machine learning, natural language processing, and live operators, to provide customer service, sales support, and other commerce-related functions.
Natural Language Processing (NLP) is the technological process in which computers derive meaning from natural human inputs. NLP-Based Conversational Bots are machine learning bots that exploit the power of artificial intelligence, which gives them a “learning brain.” These types of conversational bots have the ability to understand natural language, and do not require specific instructions to respond to questions as observed in types of chatbots such as Scripted and Structured Conversational Bots.
Previous generations of chatbots were present on company websites, e.g. Ask Jenn from Alaska Airlines which debuted in 2008 or Expedia's virtual customer service agent which launched in 2011.  The newer generation of chatbots includes IBM Watson-powered "Rocky", introduced in February 2017 by the New York City-based e-commerce company Rare Carat to provide information to prospective diamond buyers. 
Lack contextual awareness. Not everyone has all of the data that Google has – but chatbots today lack the awareness that we expect them to have. We assume that chatbot technology will know our IP address, browsing history, previous purchases, but that is just not the case today. I would argue that many chatbots even lack basic connection to other data silos to improve their ability to answer questions.
Despite the fact that ALICE relies on such an old codebase, the bot offers users a remarkably accurate conversational experience. Of course, no bot is perfect, especially one that’s old enough to legally drink in the U.S. if only it had a physical form. ALICE, like many contemporary bots, struggles with the nuances of some questions and returns a mixture of inadvertently postmodern answers and statements that suggest ALICE has greater self-awareness for which we might give the agent credit.
Jabberwacky learns new responses and context based on real-time user interactions, rather than being driven from a static database. Some more recent chatbots also combine real-time learning with evolutionary algorithms that optimise their ability to communicate based on each conversation held. Still, there is currently no general purpose conversational artificial intelligence, and some software developers focus on the practical aspect, information retrieval.