8. A system comprising: one or more computer processors; one or more computer memories; one or more modules of a global back-end taxonomy system incorporated into the one or more computer memories, the one or more modules configuring the one or more computer processors to improve exposures of listings of items stored in one or more databases of an electronic commerce system across a plurality of front-end taxonomies associated with a plurality of subsystems of the electronic commerce system, the improving comprising: identifying that a listing of an item is exposed to a plurality of users of a first subsystem of the plurality of subsystems via a set of categories of a first front-end taxonomy of the plurality of front-end taxonomies, the first front-end taxonomy being associated with the first subsystem, the listing associated with a first inventory, the first inventory associated with the first subsystem; mapping the listing of the item to a set of categories of a global back-end taxonomy of the electronic commerce system, the global back-end taxonomy being maintained independently of the first front-end taxonomy and a second front-end taxonomy of the plurality of taxonomies, the second front-end taxonomy being associated with a second subsystem of the plurality of subsystems, the mapping of the listing based on a product type of the listing; mapping a category of the set of categories of the global back-end taxonomy to a category of a set of categories of the second front-end taxonomy associated with the second subsystem, the mapping of the category based on the product type and a most common classification of other listings associated with a second inventory, the second inventory associated with the second subsystem; and exposing the listing of the item to a plurality of users of the second subsystem via the set of categories of the second front-end taxonomy based on the mapping of the listing of the item to the set of categories of the global back-end taxonomy and the mapping of the set of categories of the global back-end taxonomy to the category of the second front-end taxonomy, the exposing allowing a user of the second subsystem to access the listing associated with the first inventory from a user interface of the second subsystem.
8. A system comprising: one or more computer processors; one or more computer memories; one or more modules of a global back-end taxonomy system incorporated into the one or more computer memories, the one or more modules configuring the one or more computer processors to improve exposures of listings of items stored in one or more databases of an electronic commerce system across a plurality of front-end taxonomies associated with a plurality of subsystems of the electronic commerce system, the improving comprising: identifying that a listing of an item is exposed to a plurality of users of a first subsystem of the plurality of subsystems via a set of categories of a first front-end taxonomy of the plurality of front-end taxonomies, the first front-end taxonomy being associated with the first subsystem, the listing associated with a first inventory, the first inventory associated with the first subsystem; mapping the listing of the item to a set of categories of a global back-end taxonomy of the electronic commerce system, the global back-end taxonomy being maintained independently of the first front-end taxonomy and a second front-end taxonomy of the plurality of taxonomies, the second front-end taxonomy being associated with a second subsystem of the plurality of subsystems, the mapping of the listing based on a product type of the listing; mapping a category of the set of categories of the global back-end taxonomy to a category of a set of categories of the second front-end taxonomy associated with the second subsystem, the mapping of the category based on the product type and a most common classification of other listings associated with a second inventory, the second inventory associated with the second subsystem; and exposing the listing of the item to a plurality of users of the second subsystem via the set of categories of the second front-end taxonomy based on the mapping of the listing of the item to the set of categories of the global back-end taxonomy and the mapping of the set of categories of the global back-end taxonomy to the category of the second front-end taxonomy, the exposing allowing a user of the second subsystem to access the listing associated with the first inventory from a user interface of the second subsystem. 13. The system of claim 8 , wherein the mapping of the listing of the item to the set of categories of the global back-end taxonomy includes identifying a product type as corresponding to both the item and each of the set of categories.