1. One or more non-transitory computer-readable media storing instructions which, when processed by one or more processors, cause: a Web application retrieving logical custodian hierarchical data that specifies hierarchical relationships between a plurality of logical custodians, the Web application generating and transmitting to a client device over one or more networks, a first set of one or more Web pages which, when processed by a Web browser at the client device, provide a graphical user interface that visually depicts the hierarchical relationships between the plurality of logical custodians and includes one or more graphical user interface controls that allow a user to specify an advanced search query to be processed against a plurality of data items, wherein the advanced search query includes one or more search terms and one or more logical custodians; the Web application causing the advanced search query that specifies the one or more search terms and the one or more logical custodians to be processed against the plurality of data items to generate a set of search results that specifies one or more data items that both satisfy the one or more search terms and belong to the one or more logical custodians; and the Web application transmitting to the client device over the one or more networks, a second set of one or more Web pages which, when processed by the Web browser at the client device, provide a graphical user interface that displays the set of search results that specifies one or more data items that satisfy the one or more search terms and that belong to the one or more logical custodians.