of coordinated international activities that aimed to define sharable preservation metadata specifications. This would ensure interoperability—the ability to exchange amongst institutions and to understand the digital object metadata and its digital content. A complication was, however, the breadth of metadata needed to support the full range of digital preservation goals. Many years of expertise and effort had already gone into specifying metadata dictionaries or implementation specifications for subsets of the four categories listed above that are also used to support functions outside digital preservation. There was no point in trying to reproduce or outdo this effort. Additionally, it is not possible to define one set of metadata that applies equally to all content types or organization types. Archival records, manuscripts, and library records, for example, require different descriptive metadata; images, text-based documents, and software source code require different technical metadata. Because of this, a number of metadata definition efforts have evolved, both in a content type- or organization type-specific space and a preservation function space. Figure 1 illustrates this in a very simplified way. Several of these initiatives have reached the status of a standard or are de facto standards. In order to be flexible and apply to a wide range of contexts, general preservation metadata and metadata container specifications try to avoid content and organization specific semantics. For example, general preservation metadata will capture the file size of files, since there are no digital representations of content that don’t involve at least one file, even if the exact file size may depend on an operating system. It would not, however, capture the issue number, which applies to serials but not books, or the resolution, which applies to images but not text. To add specificity, general metadata specifications include extension methods to support content or organization specific metadata. These more specific metadata specifications provide complete sets of semantic units for specific contexts