Jerry McDonough has written an interesting and important article about XML, interoperability, and the social context of standards making: Structural Metadata and the Social Limitation of Interoperability: A Sociotechnical View of XML and Digital Library Standards Development.
Drawing on a number of examples he presents a strong conclusion:
The digital library community seems to face a dilemma at this point. Through its pursuit of design goals of flexibility, extensibility, modularity and abstraction, and its promulgation of those goals as common practice through its implementation of XML metadata standards, it has managed to substantially impede progress towards another commonly held goal, interoperability of digital library content across a range of systems. [Structural Metadata and the Social Limitation of Interoperability: A Sociotechnical View of XML and Digital Library Standards Development]
For example, he discusses how greater abstraction in design creates greater optionality in use:
... the implementation of highly abstract elements for the definition of structure provides a tremendous amount of flexibility to document encoders; there is a vast number of potential encodings of any given object in METS, with variations possible in depth of structure (do I limit my structure to musical movements or do I provide structural information to the measure level?), labeling (you say TYPE="book", I say TYPE="monograph"), and arrangement (should the Lord of Rings film trilogy be encoded as a single METS file? Three METS files? Three METS files for the individual films and a fourth representing the abstract notion of the Trilogy?). This can lead to significant variation in encoding practices, even between two institutions dealing with remarkably similar material and using the same metadata standards, as noted by (DiLauro et al., 2005).[Structural Metadata and the Social Limitation of Interoperability: A Sociotechnical View of XML and Digital Library Standards Development]
He discusses the conflicting goals of control and connection. The ability to control, to respond to local needs and conditions, promotes flexibility. The ability to connect, to efficiently exchange, promotes constraint.
The library community has emphasized flexibility in its standards making and in the past this may have made some sense: the actual exchange of data was quite limited. However, if we expect data to flow efficiently between systems and services then this becomes problematical and greater constraint is beneficial.
Via Evan Owens.