1. A computer-implemented method of assigning values to properties in a computer system having a graphical user interface (GUI) and a data storage subsystem in which data items are organized and queried using metadata properties, the method comprising: displaying a property tree, the property tree having a plurality of nodes exposing properties of a set of the data items revealed in a list view, one or more nodes of the plurality of nodes having a widget associated therewith for switching between an expanded state and a collapsed state; receiving an indication of a selection of the widget associated with the one of the plurality of nodes to switch to the expanded state; displaying an initial list including a predefined number of a set of subnodes parented by the selected one of the plurality of nodes, wherein the displayed set of subnodes in the initial list represents most-frequently-used values or most-recently-used values; upon receiving an indication to further expand the one of the plurality of nodes, invoking a carousel control that provides a circular list of the set of subnodes parented by one of the plurality of nodes, wherein invoking the carousel control comprises: (a) visibly displaying, to a user, a number of the set of subnodes within a display area, wherein the number of the set of subnodes being visibly displayed in the display area is a function of screen space of the GUI; (b) not presently displaying remaining nodes of the set of subnodes that are outside the display area, and; (c) providing one or more selectable boundaries of the display area that allow the user to resize the display area and adjust the number of the set of subnodes visibly displayed therein; receiving a selection of one or more items of the set of data items revealed within the list view; displaying a control proximate to one or more subnodes of the set of subnodes that, upon selection by the user, assigns a value to at least one property of the properties of the selected one of the set of data items; receiving a user input that selects the control proximate to the one or more subnodes of the set of displayed subnodes; ascertaining that the one or more subnodes of the set of selected subnodes is capable of assigning the value to the at least one property of the one of the set of data items based on whether the at least one property of the properties of the one of the set of data items is changeable by the user; and in response to the user input directed at the one or more subnodes of the set of selected subnodes ascertained to be capable of assigning the value to the at least one property, modifying the at least one property of the selected one or more data items of the set of data items, wherein modifying comprises adding metadata to, or removing metadata from, the selected one or more data items of the set of data items based on the value of the at least one property represented by the one or more subnodes of the set of selected subnodes.