1. A system for retrieval at a client system of content from a server system, comprising: a communication protocol that enables an asynchronous connection over a network between a client system and a server system, and allows the client system to send via the network, and within a session between the client system and the server system, a lengthening string composed of a plurality of consecutively input characters, to query the server system for string-based content, while asynchronously receiving consecutive responses from the server system as the characters are being input; a content-based cache, at the server system, which stores previous queries and corresponding result sets previously executed by the system, and which includes within its result sets content or other information previously retrieved from the server system or one or more content sources in response to the previous queries; a client object, in communication with a client software at the client system and with the communication protocol, wherein the client object receives, as input, consecutive additional characters from the client software, and while each of the consecutive additional characters are being received as input, transmits via the network to a server object at the server system one or more corresponding consecutive queries, within the session between the client system and the server system, to retrieve content from the server system, wherein each of the corresponding consecutive queries lengthens the string by the additional characters, to form a lengthening string for retrieving matching content from the server system; and a server object, in communication with the server system, and with the client object via the communication protocol, wherein the server object in response to receiving each of the corresponding consecutive queries that modify the lengthening string, automatically uses the lengthening string to query and retrieve content information from the content-based cache at the server system or from the one or more content sources that matches the lengthening string, and asynchronously returns, while the additional characters are being input and the corresponding consecutive queries are being transmitted and the lengthening string is being modified during the session, consecutive responses containing content information which increasingly matches the lengthening string, to the client object for immediate use by the client system, wherein the server system includes at least one processor.