Information Technology Reference
In-Depth Information
The ramifications of the Open World Principle are surprising, and most clear in
terms of judging whether a statement is true or false. These repercussions transform
the Open World Principle into its logical counterpart, the Open World Assumption ,
which logically states that statements that cannot be proven to be true cannot be
assumed to be false . Intuitively, this means that the world cannot be bound. On
the Web, the Open World Principle holds that since the Web can always be made
larger, with any given set of statements that allow an inference, a new statement
relevant to that inference may be found. So any agent's knowledge of the Web is
always partial and incomplete, and thus the Open World Assumption is a safe bet
for agents on the Web. The Open World Principle is one of the most influential
yet challenging principles of the Web, the one that arguably separates the Web
from traditional research in artificial intelligence and databases in practice. In these
fields, systems tend to make the opposite of the Open World Assumption, the Closed
World Assumption. The Closed World Assumption states that logically statements
that cannot be proven to be true can be assumed to be false . Intuitively, this means
that somehow the world can be bounded. The Closed World Assumption has been
formalized on a number of different occasions, with the first formalization being due
to Reiter (1978). This assumption has often been phrased as an appeal to the Law
of the Excluded Middle (
p ) in classical logic (Detlefsen 1990). Negation
as failure is an implementation of the Closed World assumption in both logic
programming and databases, where failure for the program to prove a statement
is true implies the statement is false (Clark 1978).
p
.
p
∨¬
2.3.5
Principle of Least Power
The Principle of Least Power states that a Web representation given by a resource
should be described in the least powerful but adequate language . This principle is
also normative, for if there are multiple possible Web representations for a resource,
the owner should chose the Web representation that is given in the 'least powerful'
language. The Principle of Least Power seems odd, but it is motivated by Berners-
Lee's observation that “we have to appreciate the reasons for picking not the most
powerful solution but the least powerful language” (1996b). The reasons for this
principle are rather subtle. The receiver of the information accessible from a URI
has to be able to decode the language that the information is encoded in so the
receiver can determine the sense of the encoding. Furthermore, an agent may be
able to decode multiple languages, but the owner of the URI does not know what
languages an agent wanting to access their URI may possess. Also, the same agent
may be able to interpret multiple languages that can express the same sense. So, the
question always facing any agent trying to communicate is what language to use?
In closed and centralized systems, this is ordinarily not a problem, since each agent
can be guaranteed to use the same language. In an open system like the Web, where
one may wish to communicate a resource to an unknown number of agents, each of
which may have different language capabilities, the question of which language to
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