Overall scheme of a phylotastic system. The user (upper left)experiences a phylotastic system as a piece of software that returnsa phylogeny in response to a query consisting of a list of taxa (andpossibly other qualifiers). The user’s point of access to thesystem is a client program or controller that invokes variousoperations to access (and transform) the information needed tosatisfy the user’s query. The response ultimately depends oninformation available from name-banks, source trees, andcalibrations (right). There are many ways to implement such asystem. In the approach described here, it is a system of looselycoupled components that uses web services to exchange informationusing common standards.