Transcript The Rule Markup Initiative
RuleML:
Markup von Regelwerken im Semantischen Web (Markup of Rule Systems in the Semantic Web)
Harold Boley, DFKI GmbH Online 2002, Düsseldorf, January 29 st , 2002
1
International Initiative RuleML
The Rule Markup Initiative works towards W3C submission representing its
various participants
from industry and academia First goal has thus been to provide modular system of
RuleML sublanguages
based on XML and RDF (
R
esource
D
escription
F
ramework) This led to development of novel
XML-RDF integrating Web data model
On its basis, RuleML initially defined with
hierarchy of DTDs, gradually redefined with XML Schema
To facilitate rule exchange,
XSLT-based translators between RuleML and other rule languages
have been specified RuleML Online 2002
2
Web-Based Business Rules: Merchant-Customer Exchange Scenario
(I)
Merchant 1 Merchant m
. . .
request rules on discounts etc.
Customer RuleML Online 2002 request rules on discounts etc.
preselect m best merchants (e.g., using purchasing rules)
3
Web-Based Business Rules: Merchant-Customer Exchange Scenario
(II)
Merchant 1 Merchant m publish rulebase 1
. . .
translate to standard format (e.g., RuleML) publish rulebase m compare, instantiate, and run rulebases Customer RuleML Online 2002
4
Web-Based Business Rules: Merchant-Customer Exchange Scenario
(III)
Merchant i order from Merchant i Customer RuleML Online 2002 select best deal (e.g., discount)
Web-Based Business Rules: Formalize Natural Language in Horn Logic
English Business Rules: ''The
discount percent
if the
customer
percent
if the
customer
for a
customer
is is
premium premium
buying a and the and the
product product product
is is
5.0 regular
is
luxury
.'' .'' Prolog-like formalization (with XML underpinnings):
5
RuleML Online 2002
Semantics and Pragmatics (Implementation)
Original Web:
Distributed development, usage and maintenance of HTML-based informal documents
6
Semantic Web:
Employ same infrastructure for
formal specifications or declarative programs
Which Logics/Languages?
Uniform semantic/pragmatic foundation potential:
– –
Description Logic:
RDF Schema, DAML+OIL for taxonomies
Horn Logic:
Prolog, RuleML
for ontologies for axioms RuleML Online 2002
Syntax
7
Syntactic underpinnings, however, will most likely come from
Extensible Markup Language (XML)
Fortunately,
translators between Prolog and XML
syntaxes can be defined Can also form basis for
semantic/pragmatic technology transfers between Prolog and XML
Current talk will exemplify this using
XML syntax of Rule Markup Language (RuleML)
, Version 0.8
RuleML Online 2002
8
Unify XML and RDF
XML and RDF have different data models: XML based on, possibly attributed,
left-to-right ordered, node-labeled trees
, reminiscent of parse (syntax) trees RDF based on
directed, arc-labeled (unordered) graphs
with two kinds of nodes, resources and literals, the latter not allowing outgoing arcs With the advent of the Semantic Web a unified data model would be advantageous RuleML Online 2002
9
Problem with Positional XML Markup
For marking up
3 2
, an XML element
powform
might be employed, with the positional convention
''First child is base, second child is exponent''
But without some kind of 'signature declaration' this markup could instead mean
2 3
according to a
''First child is exponent, second child is base''
convention Analogous conventions for
N
-ary operators ( number of possible interpretations
N
>2) need to disambiguate a combinatorially exploding ( Without extra information the positions of 'roles'
powform
: base and exponent) of children cannot in general be determined from some such markup RuleML Online 2002
Solution with Non-Positional RDF Markup
10
In 'object-centered' modeling and 'feature'/'frame' logics the way out is representing powers and other operators in a non-positional manner, making them
objects
with explicitly indicated
roles
for their arguments In Frame/Horn-logic-integrating F-Logic, developed for RDF in TRIPLE, our example could thus be represented as a fact:
powform [base -> 3 : integer; exponent -> 2 : integer].
RuleML Online 2002
Non-Positional RuleML Solution
Paralleling this in RuleML, we complement XML
'type tags'
by distinguished, RDF-like
'role tags' 11
Generalizing XML attributes, roles will allow values that themselves contain markup In our example we thus use
powform
and
_exponent
with
_base
subelements, where the leading ''
_
'' distinguishes roles:
RuleML Online 2002
12
Role Commutativity
There are two correctly prefixed
powform
-child permutations, which we regard as algebraically equivalent commutative markups:
=
RuleML Online 2002
Order-Labeled Combination
For the sequence
3, 9
combined with the formula
3 2
:
3
base
rational integer
9 RuleML Online 2002 3
exponent
2
integer
16
Relation Applications in RuleML
A predicate or
relation symbol
rel
element
. The
application
will in RuleML be a of an
_opr
-role embedded relation symbol to a sequence of terms is marked by an
atom
element
in RuleML Example:
travel
application
travel(john,channel-tunnel)
to two individual constants will thus be:
RuleML Online 2002
17
Facts in RuleML
Horn fact in RuleML is asserted as a
fact
element
that possesses exactly one subelement -- the _
head
-role-embedded
atom
element Example:
travel
fact (containing
travel
application)
travel(john,channel-tunnel).
becomes:
< fact > < _head >
RuleML Online 2002
Tree structure?
fact _head Subtree XML
fact
head
Subtree OrdLab
18
Derivation Rules in RuleML: Source
Horn rule in RuleML is asserted as an
imp
element
that has two subelements -- a _
head
-role
atom
element augmented (either to its right or left) by a _
body
-role
atom
or
and
element Example:
travel
rule (Datalog)
travel(Someone,channel-tunnel) : carry(eurostar,Someone).
rewritten in RuleML thus: RuleML Online 2002
19
Derivation Rules in RuleML: Markup
RuleML Online 2002
20
Derivation Rules in RuleML: Tree
Graph-theoretically, RuleML clauses are again OrdLab trees, as illustrated for this rule:
imp
head body
atom atom
opr
rel
travel
var
someone
ind
channel tunnel
opr
rel
carry
ind
eurostar
var
someone RuleML Online 2002
21
The RuleML DTD/Schema Hierarchy
Focus on 12 sublanguages of derivation rule modules: All except the 'UR' (URL/URI) group correspond to well-known rule systems, with formal semantics
ruleml
ur
URL/URI-like ‘ur’-objects
ur-equalog ur-hornlog
ur-datalog
urc-datalog equalog
Rooted DAG will be extended with branches for further sublanguages
hornlog
datalog
ur-datalog = join(ur,datalog)
bin-datalog urc-bin-datalog urc-bin-data-ground-log urc-bin-data-ground-fact RuleML Online 2002
RDF-like triples
Derivation Rules in UR-Datalog: Indexing
22
RuleML Online 2002
23
Modular Sublanguage Composition
Each node in above hierarchy, e.g. 'hornlog', is a DTD/Schema that defines syntax of this sublanguage:
Knowledge bases can refer to most specific DTD/Schema to maximize interoperability
Non-leaf nodes are composed of the -- possibly modified -- node(s) reachable via outgoing link(s) below plus possibly some extra definition parts Example: 'hornlog' is composed of a -- slightly modified -- 'datalog' plus complex terms; 'datalog' itself contains 'bin-datalog', etc.
RuleML Online 2002
From DTD to XML Schema:
rulebase
s
DTD line (XML in EBNF-like SGML subset): 24 Schema part (official way to define XML in XML):
. . .
RuleML Online 2002
From DTD to XML Schema:
imp
lications
25 DTD line (permuted _head / _body sequences): Schema part (unordered xsd:all set):
. . .
. . .
RuleML Online 2002
HTML Rendering of Business Rules
Before our XML-to-XML roundtrip: RFML version, via XML-to-HTML stylesheet
rfmlsp
, will lead to font-and-color-coded HTML Prolog version, rendered in a browser (first line is sample rule):
27
RuleML Online 2002
28
XSL Transformations from and to RuleML
Exemplary pair of 'inverse' translators ('stylesheets') exporting/importing markup between RuleML and RFML ( Relational-Functional Markup Language ), where only the logic part is needed for Prolog:
Export
via
ruleml2rfml.xsl
: Stylesheet translates Hornlog RuleML rulebase to corresponding RFML program
Import
via
rfml2ruleml.xsl
: Stylesheet translates a Hornlog RFML program to corresponding RuleML rulebase RuleML Online 2002
29
Bi-Transforming Discount Sample Rule
''The
discount < percent
if the
>
customer
for a
customer
is
premium
buying a
product
and the
product
is
5.0
is
regular
.''
< imp > <_head> < atom > <_opr>
rfml2ruleml.xsl
premium customer <_opr>
RuleML Online 2002
< hn > < pattop >
Export from RuleML: Tree Rewriting (I)
rulebase . . .
Subtree Subtree
30
rfml . . .
Subtree Subtree
What does this XML processing look like in XML?
RuleML Online 2002
Export from RuleML: Implementation (I)
31
First XSLT rule ('template') matches document root ''
/
'' followed by
rulebase
element; it 'recursively' maps ('applies') all matching templates to all
rulebase
subelements and generates
rfml
element from result:
RuleML Online 2002
32
Export from RuleML: Tree Rewriting (II)
fact _head Subtree hn Subtree RuleML Online 2002
33
Export from RuleML: Implementation (II)
Second template matches
fact apply-templates
over its element, does
_head
in
mode pattop
(for RFML's
op
erator
patt
erns), and generates
hn
element from result:
RuleML Online 2002
34
Export from RuleML: Tree Rewriting (III)
atom _opr Argterm . . .
Argterm rel PCDATA atom Argterm . . .
Argterm _opr rel PCDATA pattop con Argterm . . .
Argterm PCDATA RuleML Online 2002 Implementation details:
ruleml2rfml.xsl
Web Technology
for Prolog
37
Prepared semantic-pragmatic XML-Prolog transfers using XML syntax: http://www.dfki.de/ruleml XML-RDF-integrating
data model
used as basis for
DTD/Schema definitions
of Prolog on the Web Started semantic-pragmatic transfers in direction XML-to-Prolog by specifying (semantics-preserving)
XSLT-based translators
RuleML RFML It is now possible to build and exchange
Prolog knowledge bases over the Web
RuleML Online 2002
38
Web Technology
for General Use
: DTDs and XSLT are Still Most Practical
,
XML Schema and XQuery are Promising
Demonstrated
practical use of W3C technologies
such as DTDs and XML Schema as well as XSLT On the other hand hinted at a few problems with current version of XML Schema, hoping that more expressive version will be available in future Functional and logic programmers may also have wondered whether XSLT-based translators could be specified more concisely in future version of XSLT Perhaps XQuery can act as incentive towards formal semantics of XML queries and transformations RuleML Online 2002
Prolog Technology
for the Web
39
Corresponding transfers in Prolog-to-XML direction have already started with Mandarax, j-DREW, and other RuleML engines based on Prolog technology It may also be useful to implement (orthogonalized versions of) XML Schema, XSLT, etc. in (RuleML and) Prolog to explore limits of expressiveness that can be realized formally and efficiently Side-effect of this work could be translators between XML syntax and more concise Prolog syntax for W3C languages such as XML Schema and XSLT RuleML Online 2002