The key difference is that with directed dialogue, the user is more likely to speak an option exactly as was communicated by the prompt (e.g. "account balance"). With an open-ended prompt, however, the user is likely to include extraneous words or phrases (e.g. "I was just looking at my bill and saw that my balance was wrong."). The open-ended prompt requires a greater degree of natural language processing to extract the relevant information from the phrase (i.e. "balance"). Open-ended recognition also requires a larger grammar set, which accounts for a wider array of permutations of a given response (e.g. "balance was wrong", "wrong balance", "balance is high", "high balance"). Despite the greater amount of data and processing required for open-ended prompts, they are more interactively efficient, as the prompts themselves are typically much shorter. A mixed dialogue approach involves shifting from open-ended to directed dialogue or vice versa within the same interaction, as one type of prompt may be more effective in a given situation. Mixed dialog prompts must also be able to recognize responses that are not relevant to the immediate prompt, for instance in the case of a user deciding to shift to a function different from the current one. Higher level IVR development tools are available to further simplify the application development process. A call flow diagram can be drawn with a GUI tool and the presentation layer (typically VoiceXML) can be automatically generated. In addition, these tools normally provide extension mechanisms for software integration, such as an HTTP interface to a website and a Java interface for connecting to a database. In telecommunications, an audio response unit (ARU) is a device that provides synthesized voice responses to DTMF keypresses by processing calls based on (a) the call-originator input, (b) information received from a database, and (c) information in the incoming call, such as the time of day. ARUs increase the number of information calls handled and provide consistent quality in information retrieval. IVR systems are used to service high call volumes at lower cost. The use of IVR allows callers' queries to be resolved without a live agent. If callers do not find the information they need, the calls may be transferred to a live agent. The approach allows live agents to have more time to deal with complex interactions. When an IVR system answers multiple phone numbers, the use of DNIS ensures that the correct application and language is executed. A single large IVR system can handle calls for thousands of applications, each with its own phone numbers and script.