In this paper we present RoSeS (Really Open Simple and Efficient Syndication), a generic framework for content-based RSS feed querying and aggregation. RoSeS is based on a data-centric approach, using a combination of standard database concepts like declarative query languages, views and multi-query optimization. Users create personalized feeds by defining and composing content-based filtering and aggregation queries on collections of RSS feeds. Publishing these queries corresponds to defining views which can then be used for building new queries / feeds. This naturally reflects the publish-subscribe nature of RSS applications. The contributions presented in this paper are a declarative RSS feed aggregation language, an extensible stream algebra for building efficient continuous multi-query execution plans for RSS aggregation views, a multi-query optimization strategy for these plans and a running prototype based on a multi-threaded asynchronous execution engine.