We present the Federation Semantic Attribute Mapping System (F-SAMS), a web services based system which enables a semi-automated dynamic trust establishment mechanism for managing identity federations. We present the conceptual model which allows current members to dynamically introduce new members into the federation in a trustworthy manner, using a web of trust model. F-SAMS enables existing members to interact securely with previously unknown new members of a federation and allows them to retrieve policy and semantic information about them.