1. A method comprising performing a machine-executed operation involving instructions involving a repository that supports versioning of resources, wherein the machine-executed operation is at least one of: A) sending the instructions over transmission media; B) receiving the instructions over transmission media; C) storing the instructions onto a machine-readable storage medium; and D) executing the instructions; wherein the instructions are instructions which, when executed by one or more processors, cause the one or more processors to perform the steps of: receiving a database statement for searching across versions of a label in a repository, wherein a label is associated with no more than one version of a particular resource; determining that execution of the database statement includes an operator which, when executed, causes performance of an operation that uses a particular index, wherein the particular index indexes multiple versions of multiple resources and is based on a composite key comprising at least a first component, wherein the first component is a label identifier; and examining only entries, in the particular index, associated with the label identifier.