Vertical search is an app built around a specific industry vertical, such as jobs, real estate, classifieds, automobiles, etc.
Examples of vertical search sites are:
Practically every vertical search engine which aggregates data goes through the following steps:
Some challenges in building and running a vertical search engine include:
I'm the creator and maintainer of Flexile, a vertical search toolkit built specifically for powering aggregation-type vertical search engines. If you're looking to launch a vertical search engine, I recommend you check it out first!
I've built a couple of vertical search sites from zero to launch, using either Nutch or a hand-rolled crawler.
I'm intimately familiar with the challenges and pitfalls one usually runs into, and can generally save the team quite abit of time by pre-empting problems.
I've also designed an xml-based site definition fileformat (and a corresponding GUI) which makes it easy to outsource the creation/maintenance of rules which control crawling behavior and data extraction.