In an excellent article in the current issue of Library Hi Tech, Eric Morgan, the Digital Projects Librarian at the Hesburgh Libraries at the of the University of Notre Dame, provides examples of building services based on digital collections. As he says:

In our mind, the combination of digital humanities computing techniques - like all the services against texts outlined above - and the practices of librarianship would be a marriage made in heaven. By supplementing library collections with full text materials and then enhancing its systems to facilitate text mining and natural language processing, libraries can not only make it easier for readers to find data and information, but it can also make that data and information easier to use and understand.

• Use and understand: the inclusion of services against texts in library catalogs and "discovery systems." by Eric Lease Morgan, Library Hi Tech, Vol. 30 Iss: 1, (2012) pp.35 - 59. [subscription required]

It goes without saying that no library can develop such innovative services without actually acquiring copies of the digital information and building its own digital collection. Pointing to resources that are controlled by others limits the services that libraries can provide.