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Trust and identity on the Semantic Web

Open Data movements are gradually gaining traction; government transparency efforts in the US and the UK have begun to release data-sets, some of which are published in Linked Data form. As the range and variety of Semantic Web data publishers grows, it is increasingly important that we address the problem of trust.

Previously we discussed the challenges of a trust layer for the Semantic Web, and more recently, how we think these challenges should be faced. We are convinced that provenance and reputation information will be a crucial basis for Semantic Web trust decisions.

Reputation and provenance are by no means new subjects in the domain of Computer Science, both are grounded in substantial bodies of literature. Existing techniques will likely require some adaption in order to match the challenges of the Web of Linked Data.

Hartig and Zhao‘s provenance vocabulary for Linked Data does exactly this, taking existing provenance techniques in a Web-friendly direction, recognising the distinctions between data curation, publishing and access. To do similar for reputation mechanisms will not be prohibitively difficult, however there remains a missing piece of the technological puzzle: a system of identity.

A notion of identity is necessary for any judgement of trust in order to fully link together available information. The FOAF vocabulary gives us identifiers for people, and the FOAF+SSL proposals allow us to prove the ownership of (Web of Trust, or PKI style) digital certificates, however there is of yet no accepted means of identifying a Semantic Web software agent (e.g. a Webserver) beyond the foaf:Agent type.

In order to properly describe the identity of a Semantic Web agent we require more information than a single URI. For example, in the case of a HTTP-Based Semantic Web agent (a Webserver), metadata such as the hostname and network port is to some purposes integral to the identity of the agent. To avoid coining a new identity with every HTTP request we must have some criteria by which we judge that the other parties of different data exchanges are the same entity.

An important point to make here is that we cannot rely on declarative identities, that is we cannot count on universal uptake among Semantic Web agents of a vocabulary in which to assert identity. Thus an appropriate identity mechanism must consider both observational identities (identities coined by another agent based on its observations) and declarative identities.