7. A prototype-updating method comprising: supplying prototype digital objects or prototype items of digital content, each of said prototypes having one or more quantifiable attributes; outputting prototypes supplied by prototype-issuing means, for presentation to a user; registering descriptive tag(s) assigned to specified prototypes; receiving input from a user and discriminating prototype-update commands input by the user; developing models of the relationships between tags assigned to a prototype and the prototype attributes, the model-development step comprising analysis of the values of attributes of a plurality of tagged prototypes and the assigned tags thereof; identifying the prototype to be updated; identifying update data in a prototype-update-command input by the user, wherein the update data identifies a set of one or more specified tags and defines a degree to which the specified tags describe the updated prototype for output in response to the prototype-update-command; selecting, from among the supplied prototypes, the updated prototype for output in response to the prototype-update-command, the selecting step further comprising: assessing the degree of global similarity between the prototype-to-be-updated and respective candidate prototypes, for each of the tags specified in the prototype-update command, quantifying the descriptive power of said specified tag for respective candidate prototypes by application of the tag model developed for the specified tag in the developing step, checking candidate prototypes to determine, based on the descriptive power values quantified in the quantifying step, whether the tags specified in the update data describe the candidate prototypes to the degree defined by the prototype-update command, and selecting as the updated prototype a prototype which is assessed, in the global-similarity-assessing step, to be globally similar to the prototype-to-be-updated and which is determined, in the checking step, to be described by the tags specified in the update data to the degree defined by the prototype-update-command; and outputting, in response to reception of a prototype-update command, the candidate prototype selected in the selecting step.
7. A prototype-updating method comprising: supplying prototype digital objects or prototype items of digital content, each of said prototypes having one or more quantifiable attributes; outputting prototypes supplied by prototype-issuing means, for presentation to a user; registering descriptive tag(s) assigned to specified prototypes; receiving input from a user and discriminating prototype-update commands input by the user; developing models of the relationships between tags assigned to a prototype and the prototype attributes, the model-development step comprising analysis of the values of attributes of a plurality of tagged prototypes and the assigned tags thereof; identifying the prototype to be updated; identifying update data in a prototype-update-command input by the user, wherein the update data identifies a set of one or more specified tags and defines a degree to which the specified tags describe the updated prototype for output in response to the prototype-update-command; selecting, from among the supplied prototypes, the updated prototype for output in response to the prototype-update-command, the selecting step further comprising: assessing the degree of global similarity between the prototype-to-be-updated and respective candidate prototypes, for each of the tags specified in the prototype-update command, quantifying the descriptive power of said specified tag for respective candidate prototypes by application of the tag model developed for the specified tag in the developing step, checking candidate prototypes to determine, based on the descriptive power values quantified in the quantifying step, whether the tags specified in the update data describe the candidate prototypes to the degree defined by the prototype-update command, and selecting as the updated prototype a prototype which is assessed, in the global-similarity-assessing step, to be globally similar to the prototype-to-be-updated and which is determined, in the checking step, to be described by the tags specified in the update data to the degree defined by the prototype-update-command; and outputting, in response to reception of a prototype-update command, the candidate prototype selected in the selecting step. 9. The prototype-updating method according to claim 7 , further comprising the step of identifying, in a prototype-update-command input by the user, update magnitude data quantifying, with respect to a specified tag, the degree of change in tag descriptive power that is desired in the update, wherein the seeking step further comprises seeking candidate prototypes for which the descriptive power of the specified tag differs from the descriptive power thereof in respect of the prototype-to-be-updated by an amount equal to or greater than the degree of change indicated by the update magnitude data.