The Distributed Annotation System, DAS

Ensembl makes use of the DAS in two ways:

External data may be integrated into the website.
Ensembl data may be integrated into other applications via the Ensembl DAS server.

Integrating external DAS data

The Distributed Annotation System (DAS) is a client-server system that has been initially designed for the exchange of biological annotation information based on a standard protocol. DAS provides thus a standardised method to serve custom annotation information and to integrate data sets for display in other resources. Ensembl allows attachment and configuration of external DAS sources to several Ensembl genome browser displays:

Region overview
Region in detail
Gene/External data
Transcript/External data

Several DAS resources provided by the European Bioinformatics Institute and the Wellcome Trust Sanger Institute are already available and pre-configured by default. To turn these on and off:

Navigate to the appropriate tab and view. For example the Location tab and Region in detail section.
Click the "Configure this page" link.
Choose a track to enable from the available categories.

Further annotation information resources can be integrated into Ensembl by attaching a valid data source provided by a DAS annotation server. To attach a DAS source:

Navigate to the appropriate tab and view. For example the Location tab and Region in detail section.
Click on the "Add custom data to page" link at the left.
Click on "Attach DAS" at the left, and follow the instructions.
Save and close the window. The source will be automatically enabled.

Further details

Whilst DAS was originally designed to exchange annotations of reference sequences in chromosome or clone coordinate systems, GeneDAS and ProteinDAS are extensions to the DAS protocol used to exchange gene and protein annotations independent of genomic location information. Currently, Ensembl supports annotations based on several different coordinate systems. Some coordinate systems allow annotations which are positional in nature (i.e. refer to a location within a sequence), whereas others are concerned with text-based non-positional annotations.

The views that a particular DAS source may be displayed on depends on the data being served and the coordinate system of its annotations:

In genomic coordinate systems (e.g. chromosome, clone, contig), annotations are positional.
In gene coordinate systems (Ensembl, Entrez, HUGO or MGI), annotations are non-positional.
In protein coordinate systems (Ensembl, UniProt or IPI), annotations may be positional OR non-positional.

Ensembl supports DAS on the following sections of the website:

Region overview (positional annotations)
Region in detail (positional annotations)
Gene -> External data (non-positional annotations)
Transcript -> External data (non-positional annotations)

The extended DAS specification supported by Ensembl is described in Jenkinson AM et al., BMC Bioinformatics, 2008;9(Suppl 8):S3.

The Ensembl DAS reference server

Ensembl provides a DAS reference server which gives access to genomic sequences, the latest Ensembl gene predictions, and for some species, karyotypes and ditags. A list of the sources currently served from the Ensembl DAS reference server may be found as XML documents at:

http://www.ensembl.org/das/dsn (listing generated from the standard DAS data source name (DSN request)
http://www.ensembl.org/das/sources (a listing with extended information)

Example requests

DAS request URLs have a specific format:

protocol://site-prefix/das/data-source/command?arguments

For example:

http://www.ensembl.org/das/Homo_sapiens.NCBI36.transcript/features?segment=13:31787617,31871806: Request all transcripts (exons really) in the region [31787617,31871806] on human chromosome 13 (this is where the gene BRCA2 is located in the NCBI 36 assembly).
http://www.ensembl.org/das/Gallus_gallus.WASHUC1.reference/sequence?segment=1:1,1000: Request the first 1000 bp of the first chicken chromosome.

For more information on the DAS protocol, see our main DAS documentation.