Select object name from a drop down list when modeling

Hello all,
I need to offer the user a list of documents or databases when adding these objects into the model.
So let say when a user drop a document, instead of typing in the document name, s/he will be able to select from a drop down list of the documents that I have defined in a database.
Another example also when s/he insert a lane, then display a list of roles or departments so s/he can select from instead of a random lane name.

Thanks in advance,