How does Slickdeals do "Deal Alerts"?

I don't know if I can post this here, or where to even post it, but I want to know how Slickdeals "Deal Alerts" works.

Essentially, a user creates a string of text that they want alerts for, and Slickdeals sends them an email whenever a new deal gets posted that matches that alert.

I have a feeling it's similar to publish-subscribe, but is that all they're doing? If so, can I get an example of how exactly that's functioning?

I'm sorry if I can't ask this question here, but I want to develop a mobile app with similar functionality on Google App Engine and Android, but don't know the paradigm.