The Semantic Web and the Business Rules Approach ~ Differences
by Silvie Spreeuwenberg
My last column
ended with a promise to discuss the differences in the formal specification languages
used by the semantic web and business rules communities. I had observed that
there are differences in the expression power of the semantic web rule languages
and the business rules rule languages.
The semantic web and business rule languages also differ in how they interpret particular
expressions. I promised to give you more detail on these differences.
Keeping that promise turned out to be a great challenge. The longer I thought
about it, the more I felt that the discussion might not belong in this column.
Topics such as the following are appropriate for a textbook in formal logic
- closed world vs. open world assumption,
- higher order logic vs. first order logic,
- horn clause logic vs. predicate logic,
- deontic logic vs. non-modal languages,
- based purely on formal model theory vs. based on axioms,
- negation as failure vs. scoped negation as failure.
But are these useful topics for the average business rules professional?
I could try to explain to practitioners of the business rules approach what these
differences are about, but that might not help a practitioner do his job. Are
you really interested? I wonder... To give you a sense of this, let me
illustrate with a short explanation of the first item in the list -- closed world
vs. open world assumption.
Under a closed world assumption we assume that all relevant facts are known
-- either directly or by derivation from known facts. If something is not known,
we assume it to be false. This strategy is often applied to accepting an insurance
policy, where rules govern when an insurance policy can be accepted. In a closed
world, if we do not know (or cannot derive) that a given insurance policy is accepted,
we assume that it is not accepted.
Under an open world assumption that conclusion is not valid. Instead,
if we do not know (or cannot derive) that a policy is accepted the open world assumption
considers is that it is 'unknown' whether or not the policy is accepted; we cannot
conclude that it is 'not accepted'. Here is another example of the open world
assumption that may be more intuitive. Consider the rule "if it rains
the streets are wet." If we have no information about the weather conditions
(raining or not) and ask "are the streets wet?" we cannot conclude 'not
wet'. Instead, in an open world, when there are no facts to support a "yes,
it's wet" answer all we can conclude is that that the wetness of the streets
is not known. This is intuitive.
Rather than to continue on with each of the points above, what may interest you
more are my observations regarding the consequences of these differences for those
who work with business rules.
You do not need to understand these differences to work with business rules.
Business people have long been working with business rules without being aware
of specific different logical interpretations that may exist for their business rule
expressions. Did this lead to problems? Yes and no. Within a community,
members generally agree on a common interpretation without conscious thought.
However, it is good to be aware that problems in interpretation can arise when rules
are communicated to another community, for example to an IT department.
You need to understand these differences to work with business rules.
The several standards for business rule specification that are in development
differ on these points, and the person who will be choosing a language should know
more about these differences to be able to make the best choice. Fortunately,
that person does not need to be the businessperson who works with the rules.
Fundamentalism for one position undermines collaboration between the two communities.
I hope that the semantic web community and the business rules community will be
working more closely together in the future. What is needed for that to happen
is an attitude that we can listen and learn from each other. The new OMG standard
SBVR is a result of such an attitude. SBVR includes carefully-selected
language features and allows one to choose an interpretation that is best for a particular
 Silvie Spreeuwenberg, "The Semantic Web and the
Business Rules Approach ~ Differences and Similarities," Business Rules Journal,
Vol. 6, No. 7 (July 2005), URL: http://www.BRCommunity.com/a2005/b235.html
 as known today both from commercial rule engines and
in the standard literature of the business rules community
|standard citation for this article:
|Silvie Spreeuwenberg, "The Semantic Web and the Business Rules Approach ~ Differences
and Consequences," Business Rules Journal, Vol. 6, No. 11 (Nov. 2005),