Distributed Annotation System

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Distributed Annotation System

The Distributed Annotation System, or DAS, is a protocol for exchanging and retrieving sequence annotations, possibly from multiple sources. With DAS you don't have to store annotation data to use or display it. You only have to know how to retrieve it from a DAS server.

See the BioDas web site for a full explanation of DAS

DAS/1 and DAS/2

DAS/1 was the original release of DAS. It is widely used, and that use revealed some weaknesses in the design. DAS/2 attempts to address these weaknesses.

Preserving DAS/1 Strengths in DAS/2

  • Keep focus on location-based annotation of biological sequences.
  • Protocol, not an implementation.
    • HTTP for transport,
    • URLs for queries
    • XML for responses
    • REST-like style.
  • No Required central authority.
  • Couple XML response to URL request formats.
  • XML has been shortened, but big gain comes from client-server content format negotiation, including binary. Empty elements dropped.
  • Uses HTTP caching in the client.
  • IGB - reference client for DAS2. Integrated Genome Browser


These components work with DAS servers: