Previous Trust Metrics

Format  Representation Examples
Fuzzy undefined/marginal/complete, don't know/untrustworthy/marginal/full PGP's direc trust
Fuzzy very trustworthy/trustworthy/untrustworthy/very untrustworthy Ruth/Xu/Bhargava/Regnier's RT0
General Lattice Moreton/Twigg
General Binary (yes, no) + possible supplementary information Trust management (Blaze/Feigenbaum's PolicyMaker and KeyNote)
Integer Virtual currency {0..infinity} Trustos in ubiquitous computing (http://www.trustos.com); maybe the Nuglets in mobile ad-hoc networks (http://www.lst.inf.ethz.ch/research/publications/publications/COM_MAG_2001/COM_MAG_2001.pdf)
Integer {-infinity..infinity} Slashdot.org's Karma; Ebay's feedback rating
Integer 1-10 FOAF trust module - http://trust.mindswap.org/trustOnt.shtml
Integer {0..infinity} Chimaera (Tarah, Huitema); Free Haven (www.freehaven.net, Dingledine) direct and meta trust; Li Gong system and direct trust; PGP's parameters (number of agents); Advogato's trust metric
Integer {1..infinity} Ueli Maurer's deterministic trust
Integer {-1..4} Abdul-Rahman/Hailes; Poblano (www.jxta.org/docs/trust.pdf)
Logical Binary (true, false) Cryptographic logics (Burrows/Abadi/Needham' BAN, Gong/Needham/Yahalom's GNY, Syverson/van Oorschot's SvO); Freenet (www.freenetproject.org); Lars Rasmusson/Sverker Jansson; P. Venkat Rangan.; SPKI
Logical trust(trustor,trustee,action,level) where level is in {-100;100} Grandison/Sloman's SULTAN
Logical trustBL(trustor,service,trustee,,depth,blacklist) where depth is in {0..infinity} + {*} (* for ) Giorgini/Massaci/Mylopoulos/Zannone
Logical formulas Demolombe/Jones logics; Walt Teh-Ming Yao's Fidelis
Matrix Table Yao-Hua Tan
Real [0;1] Ueli Maurer's probabilistic trust; Neurogrid (www.neurogrid.net, Samuel Joseph); Sierra's (sierra.openprivacy.org, OpenPrivacy) System trust; Castelfranchi/Falcone/Pezzulo's trustfulness
Real [0;1[ BBK (Beth, Borchedring, Klein) direct trust
Real ]0;1[ IST (Jamil, Sadri, Shiri)
Real [-1;1] Marsch (http://citeseer.ist.psu.edu/marsh94formalising.html); Sierra's (sierra.openprivacy.org, OpenPrivacy) interpersonal and self trust
Vector Tuple (each component in [0;1]) Josang's opinions (belief/disbelief/uncertainty/atomicity); Narendar Shankar/William A. Arbaugh; Golbeck/Hendler/Parsia (minimum, maximum, and weighted average trust); SECURE (support, inconclusive, contradict)
Vector Emotional Bank Account (EBA) Tuple of 3 fields in a given virtual currency (amount of money paid by the trustee in terms of actions; money lost due to these actions; some money, which is not yet known to be gained or lost) Trustee's EBA(100,12,4): the trustor has gained 100 trustos from this trustee, lost 12 trustos and 4 trustos are still not processed (http://www.cs.tcd.ie/publications/tech-reports/reports.04/TCD-CS-2004-37.pdf) ; the term Emotional Bank Account is from Stephen Covey's 7 habits of highly effective people
Vector Tuple (number of positive outcomes, number of negative outcomes, number of unknown outcomes) Number of positive previous experiences of an entity with another that can be transferred between two entities according to a specific process, for example, Trust Transfer, which makes the metric resistant to Sybil attacks