Items

The Demetrius repository stores two kinds of digital items (or objects): digitized items produced as surrogates for materials in some analog format (e.g. printed books, manuscripts, museum artifacts, video tapes, etc.), and 'born digital' items originally produced in machine-readable form (some e-books, scientific databases, sensor data, digital photographs, websites, etc.).

An item may be complete in one file (e.g. a report issued as a PDF), or it may consist of multiple linked files (e.g. an HTML page and in-line images), or it may consist of multiple files and the structural metadata needed to tie them together (e.g. a book digitized as page images). In this sense, items in Demetrius are equivalent conceptually to the items that may be found within library holdings, museum collections, and archival collections.

Within the context of the Demetrius repository, collections consist of items (see Collections). Obviously, no hard and fast line can be drawn between items and collections. Our definition of an items extends to complex works such as digitally reformatted books, but not as far as a collection (which in this case would include, for example, two or more digitally reformatted books). A digital item may belong to more than one digital collection. These destinctions are further explained in the Demetrius Items, Collections and Communities section of this web site.

The following principles apply to good objects:

1. A good digital item will be produced in a way that ensures it supports collection priorities, while maintaining qualities contributing to interoperability and reusability. More information.
2. A good item is persistent. That is, it will be the intention of some known individual or institution that the good item will remain accessible over time despite changing technologies. More information
3. A good item is digitized in a format that supports intended current and likely future use or that supports the derivation of access copies that support those uses. Consequently, a good object is exchangeable across platforms, broadly accessible, and will either be digitized according to a recognized standard or best practice or deviate from standards and practices only for well documented reasons. More information
4. A good item will be named with a persistent, unique identifier that conforms to a well-documented scheme. It will not be named with reference to its absolute filename or address (e.g. as with URLs and other Internet addresses) as filenames and addresses have a tendency to change. Rather, the stable identifier can be resolved (mapped) to the actual address. More information
5. A good item can be authenticated in at least three senses. First, a user should be able to determine the origins, structure, and developmental history (version, etc.) of the item. Second, a user should be able to determine that the items is what it purports to be. Third, a user should be able to determine that the items has not been corrupted or changed in an unauthorized way.
6. A good items will have associated metadata. All good items will have descriptive and administrative metadata. Some complex items will have structural metadata. More information

Source: adapted from 'A Framework of Guidance for Building Good Digital Collections', published by the National Information Standards Office, 2nd edition, 2004.