''Alastair, you can use this lib and tool; DefiantJS. It enables XPath queries on JSON structures and you can test and validate this XPath:
//data[category="Politician"]
DefiantJS extends the global object with the method "search", which in turn returns an array with the matches. In Javascript, it'll look like this:
var person = JSON.search(json_data, "//people[category='Politician']");
console.log( person[0].name );
// Barack Obama