Here is a quick example of how the Syntax API accelerates development by making it easy to search for a collection of objects. In this case, I had an array with some country info, including the name. I needed to see if any documents were tagged to that country:

Step one, figure out the numeric id of the country:

pxdb_import( 'content.output.pxdb_picktable' );
$country_picktable = new pxdb_picktable( 'country' );    
$pick_id = $country_picktable->lookup_value( $country['name'] );

Step two, use a Document Collection to find matching records:

$documents = new DocumentCollection();
$documents->findByCountries( $pick_id );
$documents->execute();

If you use dbasis to generate the code for your abstract collection object, it will create methods for filtering/finding by any relationship or pick field in your object.