Preservation and Access Repository (DRS)

The Digital Repository Service (DRS) is the Library's digital preservation and access repository, in production since October 2000. It is the centerpiece of the Library's digital preservation program and was recently modified as part of a multi-year project called DRS 2. The new DRS supports an object-based data model.


For information about becoming a DRS depositor, the depositing process, using the delivery services or the maintenance applications see the DRS & Delivery Systems. Continue reading to learn about the conceptual foundation and preservation services provided by the DRS.

DRS Object Model

DRS content is modeled at three levels of granularity: object, file and bitstream.

  • An object in the DRS is a coherent set of content that is considered a single intellectual unit for purposes of description, use and/or management: for example a particular book, web harvest, serial or photograph.
  • A file is a named and ordered sequence of bytes that is known to an operating system. A file can have zero or more bytes and has a file format, access permissions, and file system characterizations such as file size and last modification date.
  • A bitstream is contiguous or non-contiguous data within a file that has meaningful properties for preservation or access purposes.

DRS objects are composed of one or more files. Files are composed of zero or more bitstreams. A file can be contained by at most a single object. Files are not shared among objects - each file can belong to a single object. A bitstream may contain other bitstreams but can be contained by at most a single file. While DRS material is always modeled at the object and file levels, material is only modeled at the bitstream level when it is deemed meaningful for preservation or access purposes.

All DRS objects have a single descriptor file in METS format that contains descriptive, administrative and structural metadata about the object, its files and bitstreams.

DRS Content Models

In the new DRS, every DRS object conforms to a single "content model". Content models define types of objects supported by the DRS. Each content model definition documents:

  • supported file formats
  • file and object relationships
  • roles and other metadata
  • known delivery and rendering applications
  • associated assessments and preservation plans

The content models currently supported in the new DRS are:

  • Audio
  • Color Profile
  • Document
  • Opaque
  • Opaque Container
  • PDS Document
  • Still Image
  • Target Image
  • Text