The importance of attribution is becoming evident due to its relevance in particular for Opinion Analysis and Information Extraction applications. Attribution would allow to identify different perspectives on a given topic or retrieve the statements of a specific source of interest, but also to select more relevant and reliable information. However, the scarce and partial resources available to date to conduct attribution studies have determined that only a portion of attribution structures has been identified and addressed. This paper presents the collection and further annotation of a database of attribution relations from the Penn Discourse TreeBank (PDTB) (Prasad et al., 2008). The aim is to build a large and complete resource that fills a key gap in the field and enables the training and testing of robust attribution extraction systems