Wednesday, October 22, 2008

Alphabet Poster

Grandson Charlie (age nearly 6) rang the other night to tell me the animals he had found for the animal alphabet we had discussed the previous night. I thought it would be a neat present to make a program to create a poster by fetching images from the web for each of his words and lay it out as a poster. I like the idea of writing programs as gifts, but Charlie would prefer something real- like a climbing wall!

I thought of using Flickr, or Google images, then settled on using Wikipedia, searched via dbpedia.

There are generally two images included in the dbpedia data - foaf:img - a full size JPEG image and foaf:depiction a GIF thumbnail. The thumbnails are fine for this job.

The SPARQL query to get the thumbnail for an image is rather simple:

PREFIX foaf: <>
:Hedgehog foaf:depiction ?img.

The XQuery script parses the list of words and for each word, uses this query to get the uri of the wikipedia image. The trickiest part was laying out the poster. I struggled to do the gallery layout in CSS alone but could not get this to work with an image + caption. In the end I reverted to a table layout with a width parameter.

The functional XQuery requires the layout to be done in two stages: first generate the table cells in the right, sorted order. Then compute the number of rows required for the given number of columns and generate the table, indexing into the cell sequence to layout the cells in order. In an imperative language, or a language which did not require that every constructed element was well-formed, the two task can be merged. The approach necessitated by the functional language feels cleaner but I'd prefer to write this as a pipeline: sort the words > generate the image cells > layout the table without the need to resolve the structure clash (a Jackson Structured Programming term) between the image order and the table order via a random access into a sequence. The co-routines in Python would make a better solution I feel. XML Pipelines might help but they feel too heavyweight for this minor task.

Charlies Animals so far.

The XQuery Script is in the Wikibook

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