This paper presents DIAS,a distributed alert service for digital libraries, currently under development in project DIET.We
first discuss the models and languages for expressing user profiles and notifications. Then we present the data structures,
algorithms and protocols that underly the peer-to-peer agent architecture of DIAS.
This work was carried out as part of the DIET (Decentralised Information Ecosystems Technologies)project (IST-1999-10088),within
the Universal Information Ecosystems initiative of the Information Society Technology Programme of the European Union.