[Biojava-l] Change Proposal regarding References

[Richard HOLLAND]

Hi all,

This is a two-pronged change proposal - first to allow BioJava to make correct use of the bioentry_dbxref tables in BioSQL, and second to allow it to parse reference information correctly from EMBL, Genbank, Genpept, GenXML, and SwissProt records and store them within Sequence objects in a consistent manner.

Currently, references are loaded from only some of the above formats. Depending on the format, they are stored in different ways within Sequence object. 

Genbank references are stored with each line of the record as a separate annotation. eg. one annotation with a key saying REFERENCE and value giving a location, another with a key saying AUTHOR and a value listing them, etc. etc. As simple String/String annotations, they get persisted to the bioentry_qualifer_value table in BioSQL. As multiple references are read, they get stored with the same keys, so you end up with Annotations for these keys containing ArrayLists of potentially different arity, depending on which of the original references had which optional fields included (eg. PUBMED or MEDLINE). This makes it impossible to accurately reconstruct the original reference information when exporting the sequence to a file.

EMBL/Swissprot references do almost the same thing, except the parser here gathers up the various reference tags from the file and wraps each set in its own ReferenceAnnotation class, which is just a map which gets flattened out and persisted to bioentry_qualifier_value as String/String annotation pairs as above. When loaded back in from BioSQL the ReferenceAnnotation objects are not recreated, and you end up with the same ArrayList problem as above, leading to the same problem when trying to export the sequence to a file.

Another problem here is that the two approaches only understand their own methods when it comes to exporting references in their own file formats. So, the Genbank exporter cannot export references that were loaded from EMBL/Swissprot, and vice versa.

Not good!

So, I propose the following:

	1) Change the file format parsers above to create, when reading sequences from file, an org.biojava.bibliography.BibRef objects for each inputted reference. This object can then be stored against the Sequence as an annotation, with the key of BibRef.class. As with all other kinds of annotation, if multiple references are loaded then the value of the annotation should be an ArrayList of the various BibRef objects. If only one reference is loaded, then the value should be the single BibRef object itself.
	2) Change the file format parsers above to understand, when writing sequences to file, how to convert BibRef annotations into their own formats.
	3) There is no restriction on which of the established BibRef subtypes from org.biojava.bibliography.* you can actually use to annotate the sequence. Usually you'll be wanting a BiblioJournalArticle object. However, you MUST use certain fields as follows:
		a) use the 'identifier' field to store the PubMed or MedLine ID (purely the ID, not prefixed with anything).
		b) use the 'publisher' field to store a BiblioOrganisation object with name set to 'PUBMED' or 'MEDLINE' as appropriate (must be upper case - if not, it will get changed to upper case on persistence to BioSQL, so you might as well stick it in upper case to start with).
		c) use the 'type' field to store a TYPE_* value from BibRefSupport to indicate what sort of resource this reference refers to (in most cases you'll want TYPE_JOURNAL_ARTICLE).
	4) To alter BioSQLSequenceDB.persistBioentryProperty() to check for annotations with the key of BibRef.class or any of its established subtypes as above, and use special behaviour to persist these to the bioentry_dbxref table (and related tables as appropriate).
	5) To alter BioSQLSequenceAnnotation.initAnnotations() to check for and load the bioentry_dbxref data as BibRef.class annotations.

Any suggestions/changes/volunteers/violent objections? I can manage steps 4 and 5 myself quite easily, but will need help from everyone out there in updating the file parsers to use this proposed mechanism.

cheers,
Richard

Richard Holland
Bioinformatics Specialist
Genome Institute of Singapore
60 Biopolis Street, #02-01 Genome, Singapore 138672
Tel: (65) 6478 8000   DID: (65) 6478 8199
Email: hollandr at gis.a-star.edu.sg
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