DAS/2.1 Sources Document Specification for Genome Data Retrieval
A DAS server supplies information about genomic sequence data sources. The collection of all sources, each data source, and each version of a data source are accessible through a URL. All three classes of URLs return a document of content-type 'application/x-das-sources+xml' though likely with differing amounts of detail. A 'versioned source' request returns information only about a specific version of a data source. A 'source' request returns the list of all the versioned source data for that source. A 'sources' request returns the list of all the source data, including all the versioned source data.
The URLs might not be distinct. For example, a server with only one version of one data source may use the same URL for all three documents, and a server for a single organism may use the same URL for the 'sources' and 'source' documents.
Most servers will list only the data sources provided by that server. Some servers combine the sources documents from other servers into a single document. These registry servers act as a centralized index and reduce configuration and network overhead. A registry server uses the same sources format as an annotation server.
Here is an example of a simple sources document which makes no distinction between the three sources categories. It, like the other new DAS formats, is in XML. All of the DAS elements are in the XML namespace http://biodas.org/documents/das2. This namespace is reserved and authors of DAS extensions may not create new XML elements in it.
Example request and response
Content-Type: application/x-das-sources+xml <?xml version="1.0" encoding="UTF-8"?> <SOURCES xmlns="http://biodas.org/documents/das2" xml:base="http://www.example.com/das/genome/"> <SOURCE uri="yeast.xml" title="Saccharomyces cerevisiae (Baker's yeast) genome" doc_href="http://www.example.com/yeast.html"> <VERSION uri="yeast.xml" created="2005-12-05"> <COORDINATES uri="http://sanger.ac.uk/das-registry/yeast-32-gene" taxid="4932" source="Gene_ID" authority="SGD32" version="3"/> <CAPABILITY type="features" query_uri="features.xml" /> <CAPABILITY type="types" query_uri="types.xml"/> </VERSION> </SOURCE> </SOURCES>
All identifiers and href attributes in DAS documents follow the XML Base specification when resolving partial identifiers and href attributes. In this case the relative id "yeast.xml" is fully resolved using the xml:base of "http://www.example.com/das/genome/" to "http://www.example.com/das/genome/yeast.xml". If the result after resolving through all the parent xml:base attributes is still a relative URL then it is resolved once more with respect to the URL used to fetch the document.
Example request and response (complex)
Here is an example of a more complicated sources document with multiple organisms each with multiple versions. Each of the two source documents (one for each organism) has a distinct URL as does each of the version for each organism. This is a pure registry server because the actual annotation data comes from other machines.
Content-Type: application/x-das-sources+xml <SOURCES xmlns="http://biodas.org/documents/das2"> <SOURCE uri="http://das.ensembl.org/das/SPICEDS/" title="das_vega_trans"> <VERSION uri="http://das.ensembl.org/das/SPICEDS/127/" created="2005-05-23"> <MAINTAINER email="email@example.com" /> <COORDINATES uri="http://sanger.ac.uk/das-registry/zv4-25-chr" taxid="7955" source="Chromosome" authority="ZV4" version="25" test_range="name=BX255914" /> <CAPABILITY type="segments" query_uri="http://www.ebi.ac.uk/das-srv/genome/zebrafish-62" /> <CAPABILITY type="features" query_uri="http://das.ensembl.org/das/SPICEDS/127/features"> <SUPPORTS name="das2queries" /> </CAPABILITY> <CAPABILITY type="types" query_uri="http://das.ensembl.org/das/SPICEDS/127/types" /> </VERSION> <VERSION uri="http://das.ensembl.org/das/SPICEDS/128/" created="2005-08-13"> <MAINTAINER email="firstname.lastname@example.org" /> <COORDINATES uri="http://sanger.ac.uk/das-registry/zv4-26-chr" taxid="7955" source="Chromosome" authority="ZV4" version="26" test_range="name=BX255914" /> <CAPABILITY type="segments" query_uri="http://www.ebi.ac.uk/das-srv/genome/zebrafish-62" /> <CAPABILITY type="features" query_uri="http://das.ensembl.org/das/SPICEDS/128/features"> <SUPPORTS name="das2queries" /> </CAPABILITY> <CAPABILITY type="types" query_uri="http://das.ensembl.org/das/SPICEDS/128/types" /> <CAPABILITY type="locks" query_uri="http://das.ensembl.org/das/SPICEDS/128/locks" /> <CAPABILITY type="writeback" query_uri="http://das.ensembl.org/das/SPICEDS/128/locks" /> </VERSION> </SOURCE> <SOURCE uri="http://www.example.com/das2/mus/sources.xml" title="Mus musculus"> <VERSION uri="http://www.example.com/das2/mus/42/sources.xml" created="2006-02-11"> <MAINTAINER email="email@example.com" /> <COORDINATES uri="http://sanger.ac.uk/das-registry/yeast-12-clone" taxid="10090" source="Clone" authority="Ensembl" test_range="name=AL935121" /> <CAPABILITY type="features" query_uri="http://www.example.com/cgi-bin/features-mus-v42.cgi"> <SUPPORTS name="das2queries" /> </CAPABILITY> <CAPABILITY type="types" query_uri="http://www.example.com/das2/mus/v42/types.xml" /> </VERSION> </SOURCE> </SOURCES>
Each SOURCE id and VERSION id is fetchable. Fetching the URL "http://das.ensembl.org/das/SPICEDS/" returns a sources document with the SOURCE record for "das_vega_trans" and both of its VERSION subelements and fetching "http://das.ensembl.org/das/SPICEDS/128/" returns a sources document with only the second of its VERSION subelements.
DAS documents refer to other documents through URLs. There are no restrictions on the internal form of the URLs, other than the query string portion. Server implementers are free to choose URLs which best fit the architecture needs. For example, a simple DAS server may be implemented as a set of XML files hosted by a standard web server while more complex servers with search support may be implemented as CGI scripts or through embedded web server extensions. The URLs do not need to define a hierarchical structure nor even be on the same machine. Compare this to the DAS1 specification where some URLs were constructed by direct string modification of other URLs.
A sources request is a request for information about the data sets available from a DAS server. This may be a list of all data sources, a list of all versions of a given data source, or information about a specific version. All three are done by fetching a sources document given a URL. The returned format is identical for all three cases, except that some portions will require one element instead a list of zero or more elements.
The sources request does not use query parameters. A future version of DAS/2 may add optional query parameters to the sources request, but for now servers should respond with an HTTP error code 400 "Bad Request" if any query parameters are included.
Example response document
[Do we need this example in addition to the above?]
The response document looks like the following:
Content-Type: application/x-das-sources+xml <?xml version="1.0" encoding="UTF-8"?> <SOURCES xmlns="http://biodas.org/documents/das2" xml:base="http://dev.wormbase.org/das/genome/"> <MAINTAINER name="Yoyodyne DNA Systems" email="firstname.lastname@example.org" href="http://www.example.com/" /> <SOURCE uri="volvox" title="Volvox Database" doc_href="http://www.example.org/volvox_db.pdf"> <VERSION uri="volvox/build_1" title="Build 1, October 2002" writeable="no" created="2002-10-15" modified="2002-10-25T09:56:23"> <MAINTAINER name="Volvox helpdesk" email="email@example.com" /> <COORDINATES uri="http://ncbi.nlm.nih.gov/das-genomes/human-35" taxid="3066" source="chromosome" authority="NCBI" version="35" /> <COORDINATES uri="http://embl.ebi.ac.uk/genome/volvox-clone" taxid="2034" source="clone" authority="EMBL" /> <CAPABILITY type="segments" query_uri="volvox/1/segments"> <FORMAT name="fasta"/> <FORMAT name="raw"/> </CAPABILITY> <CAPABILITY type="types" query_uri="volvox/1/types"> <FORMAT name="das2xml" /> </CAPABILITY> <CAPABILITY type="features" query_uri="volvox/1/features"> <FORMAT name="das2xml" /> </CAPABILITY> <CAPABILITY type="locks" query_uri="volvox/1/locks" /> </VERSION> </SOURCE> </SOURCES>
The root element is named SOURCES. The MAINTAINER element is optional. A server should provide at least one of the 'name', 'email' or 'href' attributes. The 'name' is short human-readable text, the 'email' is an email address and the 'href' is a URL meant for a human using a web browser. The MAINTAINER element under the SOURCES element designates the maintainer for the server, which may be different than the maintainer for the data sources.
The SOURCES element has zero or more <a href="#link_element">LINK elements</a> linking the sources document to some other document.
The SOURCES element has zero or more SOURCE elements. The 'uri' attribute is a URI and must be a unique identifier within a SOURCES document. It should be fetchable and if fetchable it must respond with a sources document describing the given data source. The 'title' is a short label describing the source to people. The optional 'description' contains up to a paragraph of text (no HTML markup) with more details about the data source. The optional 'doc_href' is a URL for a web browser to display human-readable documentation.
A SOURCES element may have an optional MAINTAINER element. The syntax is the same as the one at the SOURCES level. If present it contains the contact information for the maintainer of the given data source. If not present clients may use the SOURCES MAINTAINER as the SOURCE MAINTAINER.
A data source may have multiple VERSION elements. The definition of what constitutes a new version is left to the data provider. VERSION elements should be listed in creation time order, with the oldest versions first. The 'uri' attribute is a URI and must be a unique identifier within the data source. It should be fetchable and if fetchable it must respond with a source document describing only the specific versioned data source. The 'title' is a short label describing the version to people. The optional description contains up to a paragraph of text (no HTML markup) with more details about the version. The optional 'doc_href' is a URL for a web browser to display human-readable documentation.
The optional 'created' and 'modified' attributes are ISO timestamps specifying when the version was first made available and most recently modified.
Each VERSION element may contain an optional MAINTAINER element, which has the same syntax and meaning as the MAINTAINER element at the SOURCES and SOURCE level. It contains the contact information for the maintainer of the specific version of the data source, which may be different than the maintainer for the data source or for the server. If the VERSION MAINTAINER is not present, clients may use the SOURCE MAINTAINER instead for contact information and if that does not exist clients may use the SOURCES MAINTAINER.
The COORDINATES element characterizes a coordinate system used by the versioned source. Each COORDINATES has a 'uri' attribute which exactly identifies the coordinate system. If two annotation servers have a COORDINATES with the same uri then they annotatate the same system. Coordinate system URIs for human and many model organism genomes are currently listed at http://www.biodas.org/wiki/GlobalSeqIDs. This list will soon be incorporated into the Sanger DAS/2 registry.
To help people select an appropriate coordinate system to use, the COORDINATES element contains a set of attributes with additional details. The 'authority' attribute is the name of the organization that determined the coordinate system. It is a name like 'NCBI', 'EMBL', 'Ensembl', 'HUGO_ID', 'IPI' or 'UniProt'. The 'source' attribute refers to the physical dimension of the coordinate system. It is a name like 'Chromosome', 'Clone', 'Contig', 'Gene_ID', 'NT_Contig', 'Protein Sequence', 'Protein Structure', or 'Scaffold'. The Sanger registry contains a full list of these restricted vocabulary terms.
The optional 'version' contains the version name of the build upon which the coordinate system is based. The optional 'created' attribute is the ISO timestamp for the coordinate system and is used when sorting by time, as when identifying the most recent version. The optional 'taxid' attribute is the NCBI taxonomy id of the organism, as a number.
The COORDINATES element may contain an optional 'test_range' attribute used to test that the server is operational. Experience with DAS1 found that the web interface code often did not catch errors at the database interface layer and would return empty results instead of correctly reporting errors. The test_range attribute contains a <a href="#feature_filters">feature filter query string</a> which can be passed to the "feature" CAPABILITY query_uri. The response after doing that feature filter request must contain at least one feature and should contain no more than a modest number.
A versioned source may have more than one COORDINATES element. For example, features may be given in both chromosome and contig space, or in human and mouse coordinates.
The CAPABILITY elements describe what sort of queries a client may do with the versioned source data. The query is done through the URL listed in the 'query_uri' field. Different query URLs support different query interfaces. The specific interface is listed in the 'type' field. The specification defines the following query URL types:
|'type' value||for information about|
|segments||description of the regions on which features are located|
|types||the feature types|
Relative 'query_uri's are resolved according to the current xml:base.
A CAPABILITY has zero or more FORMAT elements, each with a 'name' attribute. These list the supported formats for the given capability. To get the document in a given format, use the format's name in the "format" parameter of the query.
A CAPABILITY has zero or more SUPPORTS elements, each with a 'name' attribute. These list the available extensions supported by the given capability.
The segments portion of the specification describes in more detail how the FORMAT and SUPPORTS elements are used.