<?xml version="1.0" encoding="UTF-8"?>
<xs:schema 
targetNamespace="http://www.ruleml.org/0.89/xsd" 
xmlns="http://www.ruleml.org/0.89/xsd"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
>

	<xs:annotation>
		<xs:documentation xml:lang="en">
			XML Schema for a Horn-Logic RuleML sublanguage with equational logic
			File: hornlogeq.xsd
			Version: 0.89
			Last Modification: 2005-04-12
		</xs:documentation>
	</xs:annotation>
	
	<!-- equalog includes the 'equality' module -->
	<xs:include schemaLocation="modules/equality_module.xsd"/>

	<!-- note the addition of Equal and Nanos from the equality module -->
	<xs:redefine schemaLocation="hornlog.xsd">

		<!--
			add Equal so that formula's content model (below top level And) is:
			( Atom | Implies | Equivalent | Forall | Equal )
		-->
		<xs:group name="formula-top-and.content">
			<xs:choice>
				<xs:group ref="formula-top-and.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>	
		</xs:group>
		<!--		
			note that the above indirectly adds Equal to top level And so that its content model is:
			( oid?, (formula | Atom | Implies | Equivalent | Forall | Equal)* )	
		-->

		<!--
			add Equal so that head's content model is:
			(Atom | Equal)
		-->
		<xs:group name="head.content">
			<xs:choice>
				<xs:group ref="head.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		
		<!--
			add Equal so that body's content model is:
			(Atom | And | Or | Equal)
		-->
		<xs:group name="body.content">
			<xs:choice>
				<xs:group ref="body.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--
			note that the above indirectly adds Equal to Implies so that its content model is:
			( oid?, ( head, body) | ( body, head) | ( (Atom | And | Or | Equal), (Atom | Equal) ) )
		-->		


		<!--
			add Equal so that formula's content model under Forall is:
			( Atom | Implies | Equivalent | Forall | Equal )		
		-->
		<xs:group name="formula-forall.content">
			<xs:choice>
				<xs:group ref="formula-forall.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--		
			note that the above indirectly adds Equal to Forall so that its content model is:
			( oid?, (declare | Var)+, (formula | Atom | Implies | Equivalent | Forall | Equal) )
		-->

		<!--
			add Equal so that formula's content model under Exists is:
			( Atom | And | Or | Exists | Equal )		
		-->
		<xs:group name="formula-exists.content">
			<xs:choice>
				<xs:group ref="formula-exists.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--		
			note that the above indirectly adds Equal to Exists so that its content model is:
			( oid?, (declare | Var)+, (formula | Atom | And | Or | Exists | Equal) )
		-->


		<!--
			add Equal so that content's content model (under Query) is:
			(Atom | And | Or | Exists | Equal)
		-->
		<xs:group name="content-query.content">
			<xs:choice>
				<xs:group ref="content-query.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--
			note that the above indirectly adds Equal to Query so that its content model is:
			(content | Atom | And | Or | Exists | Equal)
		-->		

		<!--
			add Equal so that formula's content model (below And & Or) is:
			(Atom | And | Or | Equal)
		-->
		<xs:group name="formula-and-or.content">
			<xs:choice>
				<xs:group ref="formula-and-or.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<xs:group name="formula-and-or-head.content">
			<xs:choice>
				<xs:group ref="formula-and-or-head.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--
			note that the above indirectly adds Equal to And & Or so that their content models are:
			( (formula | Atom | And | Or | Equal)* )
		-->

		<!--
			add Equal so that torso's content model is:
			(Atom | Equal)
		-->
		<xs:group name="torso.content">
			<xs:choice>
				<xs:group ref="torso.content"/>
				<xs:element ref="Equal"/>
			</xs:choice>
		</xs:group>
		<!--
			note that the above indirectly adds Equal to Equivalent so that its content model is:
			( oid?, ( (torso, torso) | ( (Atom | Equal), (Atom | Equal) ) ) )
		-->		
		
	</xs:redefine>

</xs:schema>
