<?xml version="1.0" encoding="utf-8"?>
<RuleML xmlns="http://ruleml.org/spec"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ruleml.org/spec http://www.ruleml.org/1.0/xsd/datalog.xsd">

  <!-- start XML comment ...

Note: This is a compact (i.e. minimally-roled) version of this example.

This example rulebase contains four rules.
The first and second rules are implications; the third and fourth ones are facts.

In English:

The first rule implies that a person owns an object
if that person buys the object from a merchant and the person keeps the object.

As an OrdLab Tree:

Implies~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          |                         |
          |                         |
          |                         |
        Atom~~~~~~~~~~~~~~~~~~     And~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                 |     |     |           |                                   |
                 |     |     |           |                                   |
                 |     |     |           |                                   |        
                Rel   Var   Var        Atom~~~~~~~~~~~~~~~~~~~~~~~~~~~     Atom~~~~~~~~~~~~~~~~~~
                 .     .     .                  |     |      |       |              |     |     |
                 .     .     .                  |     |      |       |              |     |     |
                 .     .     .                  |     |      |       |              |     |     |
                own  person object             Rel   Var    Var     Var            Rel   Var   Var
                                                .     .      .       .              .     .     . 
                                                .     .      .       .              .     .     .
                                                .     .      .       .              .     .     .
                                               buy  person merchant object        keep  person object

... end XML comment -->
  <Assert mapClosure="universal">
    <Implies>
      <!-- explicit 'And' -->
      <And>
        <Atom>
          <Rel>buy</Rel>
          <Var>person</Var>
          <Var>merchant</Var>
          <Var>object</Var>
        </Atom>
        <Atom>
          <Rel>keep</Rel>
          <Var>person</Var>
          <Var>object</Var>
        </Atom>
      </And>
      <Atom>
        <Rel>own</Rel>
        <Var>person</Var>
        <Var>object</Var>
      </Atom>
    </Implies>
    <!-- The second rule implies that a person buys an object from a merchant
if the merchant sells the object to the person. -->
    <Implies>
      <Atom>
        <Rel>sell</Rel>
        <Var>merchant</Var>
        <Var>person</Var>
        <Var>object</Var>
      </Atom>
      <Atom>
        <Rel>buy</Rel>
        <Var>person</Var>
        <Var>merchant</Var>
        <Var>object</Var>
      </Atom>
    </Implies>
    <!-- The third rule is a fact that asserts that
John sells XMLBible to Mary. -->
    <Atom>
      <Rel>sell</Rel>
      <Ind>John</Ind>
      <Ind>Mary</Ind>
      <Ind>XMLBible</Ind>
    </Atom>
    <!-- The fourth rule is a fact that asserts that
Mary keeps XMLBible.

Observe that this fact is binary - i.e., there are two arguments
for the relation. RDF viewed as a logical knowledge representation
is, likewise, binary, although its arguments have type restrictions,
e.g., the first must be a resource (basically, a URI). -->

    <Atom>
      <Rel>keep</Rel>
      <Ind>Mary</Ind>
      <Ind>XMLBible</Ind>
    </Atom>
  </Assert>
</RuleML>

