184 Personal Content Experience: Managing Digital Life in the Mobile Age Figure 5-8. Overview of Metadata Engine database schemas. or as an attachment to an e-mail. In order to catch all incoming content and to choose what kind of harvester is needed, our framework has a Harvester Manager Component that • recognizes when the content arrives into the device; and • chooses the correct harvesters to extract metadata out of the content. Harvester Manager is actually a plug-in framework composed of two kinds of plug-ins. There are observer plug-ins that listen to different ports of the device. For example, a messaging observer plug-in listens to all messages that arrive into the device. If a new message arrives, whether it is an e-mail, an MMS, or some other kind of message, the message observer checks if it contains any known media content (for instance, image, music, or video). It notifi es the Harvester Manager about the new content, which then chooses a proper media harvester or harvesters to collect the metadata. For example, if the new content is an MP3 fi le, it launches ID3 tag harvester to extract the ID3 metadata.