Information Technology Reference
In-Depth Information
Fig. 4. Bilateral Trust Relationship (Web)
Fig. 5. Web of Trust (Global View)
and perceived individually. Thus the metric has to represent the level of trust
customized from the perspectiveofeachnode.Herebythedistanceoftwonodes,
by reason of the decreasing level of trust with transitivity, and the reputation
of a node in the Web of Trust have to be included. The problem in general is
to some extend related to the rating problem regarding websites in the Google
search algorithm. The so-called PageRank calculates the reputation level of a
website on base of the reputation of the linking pages [7]. In contrast to the
PageRank, the trust level of a node in this metric is no global value. It has to be
calculated individually from the perspective of each node. Hence, the following
requirements were set up for the metric:
1. The node, from whose perspective the trust value of the other nodes is mea-
sured, is the "root" node. All edges to the root node are not considered. The
root node has the trust value 1.
2. A trust value is calculated for all nodes of the web that can be reached over
a trust path from the root node. The trust values of these nodes are within
the interval ]1;
[. The closer the trust value is to 1, the higher is the level
of trust. For all nodes that can't be reached from the root over a trust path,
the value 0 is assigned. The value 0 means that there is no trust relationship
at all. Additionally the maximal length of a trust path can be defined in
order to limit the size of the web.
3. The final trust value is calculated on base of two factors: (a) the direct trust
factor, which is the distance between the root and a considered node. The
distance is the length of the shortest path between two nodes. The length is
the number of edges a path uses. The distance between any node and itself
is 0. With every additional node on the trust path the distance is increased
by 1. (b) the reputation factor, which includes the reputation derived from
all trust paths that point to the node. A node must not appear twice in a
trust path.
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