An externally-managed taxonomy is a logical hierarchy for a data set that is built and managed using a third-party tool. Once you include an externally-managed taxonomy in your project, it becomes a dimension whose hierarchy is managed by the third-party tool that created it.

In Developer Studio, you cannot add or remove dimension values from an externally-managed taxonomy. If you want to modify a dimension or its dimension values, you have to edit the taxonomy using the third-party tool and then update the taxonomy in your project.

It is important to clarify the difference between an externally-managed taxonomy and an externally-created dimension to determine which feature document is appropriate for your purposes. The two concepts are similar yet have two important key differences: externally-managed taxonomies and externally-created dimensions differ in how you include them in a Developer Studio project and how Developer Studio treats them once they are part of a project.