A content device may select associated content, such as adverts, for a user selected content item based on textual characterizing data for the associated content and the user selected content item. A term set characterizing the user selected content item is expanded using semantic graphs and similarity values between the expanded term set and term sets describing associated content is calculated. A specific associated content item is then selected based on the similarity values. The semantic graph based term set expansion may allow improved accuracy in selecting appropriate associated content while providing a process that is suitable for resource constrained scenarios. In particular, communication resource, memory resource, and computational resource usage may be kept low.