indtd.xml

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  <title>RuleML DTDs</title>

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        <box bgcolor="#FFCCCC">R u l e M L</box>
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<!--       <xhtml><big><b>RuleML DTDs</b></big></xhtml> -->
<h1>RuleML DTDs</h1>
<h2><a href="http://www.cs.unb.ca/~boley/">Harold Boley</a>, <a href="http://ebusiness.mit.edu/bgrosof/">Benjamin Grosof</a>, <a href="http://home.comcast.net/~stabet/">Said Tabet</a></h2>
<h2>Version History, 2001-01-25: Version 0.7</h2>
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<p>
This is a preliminary DTD draft for RuleML.
Each DTD in the evolving hierarchy corresponds to a specific RuleML sublanguage.
The DTDs use a modularization approach similar to the one in XHTML
in order to offer appropriate flexibility and accomodate
different implementations and approaches.
We will write a technical report on this system of RuleML DTDs
(see also <a href="http://www.ruleml.org/ruleml-krdtd/sld001.htm">KR Principles and DTD Modularization</a>).
</p>
  </opening>

<section>
<header>Overview</header>
<p>
The upper layer of the RuleML hierarchy of rules is discussed in our
main page's <a href="index.html#Design">design section</a>.
In that terminology, the system of RuleML DTDs presented here only covers
state-preserving rules (declarative, deductive-rewriting rules), not
state-changing rules (active, trigger rules); special tags for facts are also omitted.
</p>
<p>
This is because we think it is important to start with a subset of
simple rules, test and refine our principal strategy using these,
and then work 'up' to the more general categories of rules in the hierarchy.
For this we choose
<a href="http://www-lp.doc.ic.ac.uk/UserPages/staff/ft/alp/net/dbs/datalog.html">Datalog</a>, a language corresponding to relational databases
(ground facts without complex domains or 'constructors')
augmented by views (possibly recursive rules),
and work a few steps upwards to further declarative rules
from (equational) Horn logic.
We also work upwards from a URL/URI language corresponding to
simple objects. The join of both of these branches then permits
inferences over RDF-like 'resources' and can be re-specialized to
RDF triples.
</p>
<p>
Regarding the concrete markup syntax, we have been experimenting
with several DTDs prior to the current, still preliminary, version.
The rationale for our current tags is as follows.
<itemize>
  <item>An explicit N-ary conjunctive tag pair
<tt>&lt;and></tt> ... <tt>&lt;/and></tt> is used,
preparing other boolean connectives
(mainly <tt>&lt;or></tt> ... <tt>&lt;/or></tt>) and their nesting.
  </item>
  <item>Using <tt>and</tt> for the conjunction of premises, rules become
binary, in particular our deductive-rewriting implication rules become
<tt>&lt;if></tt> <i>conc</i> <tt>&lt;and></tt> <i>prem1</i> ... <i>premN</i> <tt>&lt;/and></tt> <tt>&lt;/if></tt>
  </item>
  <item>The (conclusion and premise) roles of the two subelements (children) of the XML element
<tt>&lt;if></tt> <i>conc</i> <i>prem</i> <tt>&lt;/if></tt>
thus need no further markup, making it compatible to future equivalence rules
<tt>&lt;equiv></tt> <i>lequiv</i> <i>requiv</i> <tt>&lt;/equiv></tt>
and consistent to all other RuleML connectives.
  </item>
  <item>The backward <strong>notation</strong> of
<tt>&lt;if></tt> <i>conc</i> <i>prem</i> <tt>&lt;/if></tt>
does not compromise the directional neutrality of 
these state-preserving rules, but makes them consistent to
the standard notation of Horn rules and to future
directed equations.
  </item>
</itemize>
</p>
</section>

<section>
<header>Explanations</header>
<p>
Appended below is a preliminary DTD, designated version 0.7,
for the Datalog subset of RuleML (<a href="#Appendix 1">Appendix 1</a>).  Also appended
below is a simple example rulebase that conforms to that DTD, 
and instructions for how to validate the example against the
DTD.  
</p>
<p>
There now also is a family of DTD's, specified in a modular
fashion  (using parameter ENTITY declarations), also designated
vers. 0.7, at this URL: <a href="http://www.ruleml.org/dtd/0.7/">http://www.ruleml.org/dtd/0.7/</a> .
Note that this family of DTD's is, overall, more raw/immature than just 
the Datalog member of that family.  Note that the Datalog DTD on the
website is a bit more complex, but equivalent, to the one appended
below.  The one below is called "stand-alone", because it has
stripped out most of the ENTITY declarations that are in the 
website (non-"stand-alone") version.  
</p>
<p>
To see the DTD's on the website:
After you clicked on the *.dtd files, you may have to select
View | Page Source. Thus, we provide additional *.dtd.txt links.
Downloading should work anyway.
</p>
<p>
You can try things out "stand-alone", as explained in <a href="#Appendix 3">Appendix 3</a>,
using the own.ruleml example of <a href="#Appendix 2">Appendix 2</a> (Warnings here
concern only stylistic matters).
</p>
<p>
You may also use the non-"stand-alone" modules to study XML's
"INCLUDE"/"IGNORE" overriding method for DTDs that are read in via
"ENTITY % ... SYSTEM *.dtd" declarations. But you can get the gist
of the definitions also when treating most of these house-keeping
directives as no-ops.
</p>
<p>
After some discussions, we found a set of tag names that sound
reasonable to us. Feedback is very welcome.
</p>
<p>
Facts are currently simply rules ("if" elements) that have empty
(i.e. 'true') 'and' prems.  We'll need an explicit, abbreviating
tag. Similarly, perhaps, for trigger rules and integrity constraints.
</p>
<p>
User comments on all levels are already taken care of by XML;
look at the sample datalog document own.ruleml.
</p>
<p>
More sample files -- each referring to the most specific DTD still
validating them -- can be found at: <a href="http://www.ruleml.org/exa/">http://www.ruleml.org/exa/</a> .
See the instructions above (about View | Page Source, etc.) for
viewing the content etc.
</p>
</section>

<section label="Appendix 1">
<header>Appendix 1:  DTD for Datalog subset of RuleML</header>
<box bgcolor="#CCCCFF"><code><![CDATA[
<!-- An XML DTD for a Datalog RuleML Sublanguage: Stand-Alone Version -->
<!-- Last Modification: 2001-01-25 -->



<!-- ENTITY Declarations -->


<!-- a conclusion and premise will be usable within 'if' implications -->
<!-- conc element uses an atomic formula -->
<!-- prem element uses an atomic formula or an 'and' -->

<!ENTITY % conc "atom">
<!ENTITY % prem "(atom | and)">



<!-- ELEMENT and ATTLIST Declarations -->


<!-- 'rulebase' root element uses 'if' implications as top-level rules -->

<!-- label attribute allows naming of an entire individual rulebase; -->
<!-- e.g., this can help enable forward inferencing of selected rulebase(s)  -->

<!-- direction attribute indicates the intended direction of rule inferencing;  -->
<!-- it is a preliminary design choice and has a 'neutral' default value -->

<!ELEMENT rulebase (if*)>
<!ATTLIST rulebase label CDATA #IMPLIED>
<!ATTLIST rulebase direction (forward | backward | bidirectional) "bidirectional">
 
 
<!-- 'if' implications are usable as top-level rules -->
<!-- 'if' element uses a conclusion followed by a premise -->
<!-- "<if>conc prem</if>" stands for "conc if prem", i.e., "conc is true if prem is true" -->
 
<!-- label attribute is a handle for the rule: for various uses, including editing -->
 
<!ELEMENT if (%conc;, %prem;)>
<!ATTLIST if label CDATA #IMPLIED>
 
 
<!-- an 'and' is usable within premises -->
<!-- 'and' uses zero or more atomic formulas -->
<!-- "<and>atom</and>" is equivalent to "atom"-->
<!-- "<and></and>" is equivalent to "true"-->
 
<!ELEMENT and (atom*)>
 
 
<!-- atomic formulas are usable within conc's, prem's, and 'and's -->
<!-- atom element uses rel(ation) symbol followed by a sequence of -->
<!-- zero or more arguments, which may be ind(ividual)s or var(iable)s -->
 
<!ELEMENT atom (rel, (ind | var)*)>
 
 
<!-- there is one kind of fixed argument -->
 
<!-- individual constant, as in predicate logic -->
 
<!ELEMENT ind  (#PCDATA)>
 
 
<!-- there is one kind of variable argument -->
 
<!-- logical variable, as in logic programming -->
 
<!ELEMENT var  (#PCDATA)>
 
 
<!-- there are only fixed (first-order) relations -->
 
<!-- relation or predicate symbol -->
 
<!ELEMENT rel  (#PCDATA)>]]></code></box>
</section>

<section label="Appendix 2">
<header>Appendix 2:  Example RuleML document:  a rulebase with filename own.ruleml</header>
<box bgcolor="#FFCCCC"><code><![CDATA[
<?xml version="1.0" standalone="no"?>
<!DOCTYPE rulebase SYSTEM "http://www.ruleml.org/dtd/ruleml-datalog-standalone.dtd">



<rulebase>


<!-- This example rulebase contains four rules.  The third and
fourth rules are actually facts.

In English:
The first rule says that a person owns an object if that person buys
the object from a merchant and the person keeps the object. -->


<if>
  <atom>
    <rel>own</rel>
    <var>person</var>
    <var>object</var>
  </atom>
  <!-- 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>
</if>



<!--
In English:
The next rule says that a person buys an object from a merchant
if the merchant sells the object to the person. -->

<if>
  <atom>
    <rel>buy</rel>
    <var>person</var>
    <var>merchant</var>
    <var>object</var>
  </atom>
  <atom>
    <rel>sell</rel>
    <var>merchant</var>
    <var>person</var>
    <var>object</var>
  </atom>
</if>
 
 
<!-- The next rule is a fact that says, in English, that
John sells XMLBible to Mary. -->
 
<if>
  <atom>
    <rel>sell</rel>
    <ind>John</ind>
    <ind>Mary</ind>
    <ind>XMLBible</ind>
  </atom>
  <!-- empty 'and' -->
  <and/>
</if>
 
<!-- The last rule is a fact that says, in English, 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). Some of the
DTD's on the RuleML website handle URL's/URI's (UR's); see especially
urc-datalog.dtd for inferencing with RDF-like facts -->
 
<if>
  <atom>
    <rel>keep</rel>
    <ind>Mary</ind>
    <ind>XMLBible</ind>
  </atom>
  <and/>
</if>
 
 
</rulebase>]]></code></box>
</section>

<section label="Appendix 3">
<header>Appendix 3:  Instructions/Trace on Validating the example against the DTD</header>
<box><code><![CDATA[
Validating a RuleML 0.7 Sample Document: own.ruleml



> Go to]]></code>
<a href="http://www.stg.brown.edu/service/xmlvalid/">http://www.stg.brown.edu/service/xmlvalid/</a>
<code><![CDATA[

> Paste in at

URI:
http://www.ruleml.org/exa/own.ruleml


> Hit the 'Validate' button
> You should get:


Validation Results for http://www.ruleml.org/exa/own.ruleml


Warnings:

line 31, http://www.ruleml.org/dtd/ruleml-datalog-standalone.dtd: 
       warning (652): element has more than one attlist declaration: rulebase 
line 73, http://www.ruleml.org/exa/own.ruleml: 
       warning (1106): empty-tag syntax used for element not declared with EMPTY content model: and 
line 92, http://www.ruleml.org/exa/own.ruleml: 
       warning (1106): empty-tag syntax used for element not declared with EMPTY content model: and 


Document validates OK.]]></code></box>
</section>


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Site Contact:
<a href="http://www.cs.unb.ca/~boley/">Harold Boley</a>.
Page Version: 2001-02-14

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