Tuesday, July 17, 2012

How to do a BLAST from Smalltalk

Provided by the National Center for Biotechnology Information (NCBI), BLAST is a sequence homology search program that finds all the sequences that match a particular given sequence from a database, and it is considered the most fundamental tool in bioinformatics today, although there are many other similar programs for different cases. I'm not going here to review the huge literature on sequence/string matching, for what any simple search in any search engine would get you a lot of resources to start.

For remote queries, you may access the free NCBI BLAST service in two ways, from a web browser and programatically through the BLAST URL API, previously known as QBlast. In this post you may read how to use the API using Smalltalk, and downloading a file with results in XML format for later processing
| search |
search := BioNCBIWWWBlastClient new nucleotide query: 'CCCTCAAACAT...TTTGAGGAG';
   hitListSize: 150;
   expectValue: 10;
   wordSize: 11;
search outputToFile: 'blast-query-result.xml' contents: search result.
in this script, at first we set up the Blast Client with the database and query sequence. Notice at this stage you may serialize the BioNCBIWWWBlastClient instance without further parameters. The second "set" of messages are "in cascade", in Smalltalk sometimes you need to send one object several consecutive messages, and in this case are directed to configure the search and send the requests in the #fetch. Each command is implemented as a subclass of BioNCBICommand because each one (like GET or PUT) accepts specific parameter types, but you don't need to worry about the valid parameters as they are validated internally, for example, when setting the database. Each message to the Blast client builds the corresponding URL, for example a GET url:


during execution you may open a Transcript and see the request progress:

17 July 2012 6:58:51 am Fetching NCBI BLAST request identifier...
17 July 2012 6:58:53 am Parsing RTOE...
17 July 2012 6:58:53 am New RTOE = 18
17 July 2012 6:58:53 am RTOE = 18
17 July 2012 6:58:53 am RID = 0ADUV9FM016
17 July 2012 6:58:53 am Executing...BioNCBIFetch
17 July 2012 6:58:53 am QBLAST: Delaying retry for 18 seconds
17 July 2012 6:59:11 am Sending another NCBI BLAST request...
17 July 2012 6:59:14 am NCBI BLAST request sent, waiting for results...
17 July 2012 6:59:15 am Finished successfully


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