1. A method of labeling data items, comprising: at a computer system having one or more processors and memory storing programs executed by the one or more processors: identifying a first label and a second label; receiving a user specification of a first relationship between the first label and the second label and a second relationship between the second label and the first label, respectively, wherein the first relationship is distinct from the second relationship; associating the first label with the second label in accordance with the first relationship and the second relationship, respectively; applying the first label to a first subset of the data items and the second label to a second subset of the data items; in response to a selection of the first label alone, preparing for display of a first view of information associated with the first subset of the data items and information associated with the second subset of the data items based on the first relationship; and in response to a selection of the second label alone, preparing for display of a second view of information associated with the first subset of the data items and information associated with the second subset of the data items based on the second relationship; wherein the first and second labels are distinct from a logical storage scheme associated with the data items and the second view is visually distinct from the first view.