I was half hoping that it would use the draft OpenSearch Geo extensions that Andrew has been working on, but after taking a look, the API is richer in scope than what the geo extension is designed for. Though as you can see below, the geo extensions could still offer a complement to the Yelp API.
Moreover, Yelp made the perfectly reasonable choice to syndicate their search results in a JSON format (example), rather than with a more bulky XML document.
Which gets me again thinking about documenting a JSON-based output format for OpenSearch results. Given OpenSearch's agnostic relationship with syndication formats, and my own long-standing assertion that XML is merely one serialization possibility for Atom, there is nothing really stopping us from adopting JSON+OpenSearch.
In fact, here's what an OpenSearch description document might look like for a simple (i.e., not comprehensive) Yelp search request:
<?xml version="1.0" encoding="UTF-8"?>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"
xmlns:yelp="http://www.yelp.com/developers/documentation/search_api">
<ShortName>Yelp Search</ShortName>
<Description>Use Yelp.com to search local businesses.</Description>
<Tags>yelp</Tags>
<Contact>admin@example.com</Contact>
<Url type="application/json"
template="http://api.yelp.com/business_review_search?term={searchTerms}&tl_lat={yelp:tllat}&tl_long={yelp:tllong}&br_lat={yelp:brlat}&br_long={yelp:brlong}&num_biz_requested={count}&ywsid={yelp:ywsid}"/>
</OpenSearchDescription>Or even more fun, one that tweaks the Yelp API a bit to support the OpenSearch Geo notion of bounding boxes instead of explicit corners:
<?xml version="1.0" encoding="UTF-8"?>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"
xmlns:geo="http://a9.com/-/opensearch/extensions/geo/1.0/"
xmlns:yelp="http://www.yelp.com/developers/documentation/search_api">
<ShortName>Yelp Search</ShortName>
<Description>Use Yelp.com to search local businesses.</Description>
<Tags>yelp</Tags>
<Contact>admin@example.com</Contact>
<Url type="application/json"
template="http://api.yelp.com/business_review_search?term={searchTerms}&box={geo:box}&ywsid={yelp:ywsid}"/>
</OpenSearchDescription>Nice.
...
Somewhere out there is a complete version of a OpenSearch+Local spec I wrote for the old A9 local search engine... I wonder if anyone still has it; it might be worth digging up. Of course, that version used a payload of XHTML+microformats, which had some neat properties of its own.
In any case, the Yelp API is very cool. I hope to see some amazing apps built around an already fantastic service!
...
Update: Fixed a grammar error.