  This paper introduces the security and trust concepts in wireless sensor
networks and explains the difference between them, stating that even though
both terms are used interchangeably when defining a secure system, they are not
the same. The difference between reputation and trust is also explained,
highlighting that reputation partially affects trust. A survey of trust and
reputation systems in various domains is conducted, with more details given to
models in ad-hoc and sensor networks as they are closely related to each other
and to our research interests. The methodologies used to model trust and their
references are presented. The factors affecting trust updating are summarised
and some examples of the systems in which these factors have been implemented
are given. The survey states that, even though researchers have started to
explore the issue of trust in wireless sensor networks, they are still
examining the trust associated with routing messages between nodes (binary
events). However, wireless sensor networks are mainly deployed to monitor
events and report data, both continuous and discrete. This leads to the
development of new trust models addressing the continuous data issue and also
to combine the data trust and the communication trust to infer the total trust.
