"Interoperability Levels for Dublin Core Metadata", published today as a DCMI Working Draft, discusses the modeling choices involved in designing metadata applications for different types of interoperability. At Level 1, applications use data components with shared natural-language definitions. At Level 2, data is based on the formal-semantic model of the W3C Resource Description Framework. At Level 3, data is structured as Description Sets (i.e., as records). At Level 4, data content is subject to a shared set of constraints (as described in a Description Set Profile).