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The '''DLV''' ('''D'''ata'''L'''og with Disjunction, where the 
[[Logical disjunction|logical disjunction]] symbol '''V''' is used) system is a 
disjunctive [[Logic programming|logic programming]] system, implementing the 
[[Stable model semantics|stable model semantics]] under the [[Answer set programming|answer set programming]] 
paradigm. It extends the [[Datalog]] language to allow the 
use of OR in the heads of rules.

Briefly, [[Disjunctive Datalog|disjunctive Datalog]] is a variant of Datalog where disjunctions 
may appear in the rule heads; advanced versions also allow for negation 
in the bodies, which can be handled according to a semantics for negation 
in disjunctive logic programming.

== Programming example ==

The following is a program in Datalog extended with [[Negation as failure|negation as failure]]:
<source lang=Prolog>
smoker(john).
smoker(jack).

jogger(jill).
jogger(john).

healthy(X) :- jogger(X), \+ smoker(X).
</source>

This is the translation of the above program into DLV: Take Clark Completion and Clausal Form
<pre>
smoker(X) <- X=john.
smoker(X) <- X=jack.
X=john v X=jack <- smoker(X).

jogger(X) <- X=jill.
jogger(X) <- X=john.
X=jill v X=john <- jogger(X).

healthy(X) v smoker(X) <- jogger(X).
jogger(X) <- healthy(X)
<- healthy(X) & smoker(X).
</pre>
The following query has a single stable model:
<pre>
?- healthy(X).
X = jill ;
No
</pre>

== References ==
{{Reflist}}

== External links ==
* [http://www.dlvsystem.com/html/DLV_User_Manual.html DLV user manual]
* [http://www.dlvsystem.com/html/The_DLV_Tutorial.html DLV Tutorial]


[[Category:Query languages]]
[[Category:Logic programming languages]]



{{Sourceattribution|DLV|1}}