Recommended Best Practices

From the overview of current digital library systems, it is clear that interoperability, both within a system and between systems, is of primary importance for digital library systems. While information strives to be free, information systems should strive to work together.

In examining the various digital library architectures and approaches, it is apparent that there are roles for both loose and tight coupling. Coupling is defined as:

"The degree to which components depend on one another. There are two types of coupling, "tight" and "loose". Loose coupling is desirable for good software engineering but tight coupling may be necessary for maximum performance. Coupling is increased when the data exchanged between components becomes larger or more complex."
(http://www.definethat.com/define/?id=260)

In other words, where there is efficiency needed, or where complex data needs to be frequently exchanged between software components, tight coupling is often employed. For instance, in the DSpace architecture, tight coupling persists between the components in the storage layer. When the emphasis is ensuring maximum interoperability and flexibility in communication, loose coupling is employed. For instance, harvesting metadata via the OAI-PMH is a form of loose coupling between an OAI-PMH server and a harvesting client.

The recommendations layed out in this section promote the idea of loose coupling whenever possible. Loose coupling, by definition, is an approach which facilitates broad interoperability. Through the use of API's, web services, and lightweight protocols, digital libraries and digital library systems will be able to connect and share content, functionality, and services in easier, effective ways.

In addition, the recommendation to promote interoperability between digital library services also infers a knowledge of and ability to connect with other digital library services. A discovery mechanism must be made available - the mechanism should both enable both manual and automated discovery of all available digital library services, and should provide the information necessary to allow for manual or automated access to discovered services.