Enabling Reasoning with LegalRuleML

Enabling Reasoning with
LegalRuleML
Ho-Pun Lam, Mustafa Hashmi, and Brendan Scoﬁeld
RuleML 2016, presented by Guido Governatori
www.data61.csiro.au

Background
• Certain requirements needs to be fulfilled
Isomorphism
Reification (such as
Jurisdiction, Authority, and
Temporal properties)
Rule semantics
Rule validity
Defeasibility and Conflicts
resolutions
Normative effects (such as
Obligation, Permission,
Prohibition, etc) and their
persistence
. . .
2 | Enabling Reasoning with LegalRuleML | Ho-Pun Lam, Mustafa Hashmi, and Brendan Scofield

Background
Isomorphism
Rule semantics
Rule validity
resolutions
persistence
. . .
• Existing formalisms such as LKIF, ConDec, ContractLog,
RuleML lack the support to fulﬁll such requirements

Background
Isomorphism
Rule semantics
Rule validity
resolutions
persistence
. . .
• Existing formalisms such as LKIF, ConDec, ContractLog,
RuleML lack the support to fulﬁll such requirements
⇒LegalRuleML

A Sample Contract
Section 1: (Policy of Price)
1.1 A “Premium Customer” is a customer who has spent
more than $10000 in goods. Premium Customers are
entitled a 5% discount on new orders.
1.2 Goods marked as “Special Order” are subject to a 5%
surcharge. Premium customers are exempt from special
order surcharge.
1.3 . . . . . .
Section 2: (Purchase Order)
2.1 The purchaser shall follow the supplier price lists on the
supplier’s website.
2.2 The purchaser shall present supplier with a purchase order
for the provision of goods within 7 days of the
commencement date.
2.3 . . . . . .

LegalRuleML
• A rule interchange language
proposed by OASIS
• Extends RuleML with features
speciﬁc to legal domain
• Bridge the gap between natural
language description and
semantic norms
• Allows for modelling various
laws, rules and regulations into
machine readable format
Association(s)
Context
Metadata
Statements
LegalRuleML Document

LegalRuleML (cont.)
• Provides support to
model normative eﬀects
capture conﬂicting norms without making the set of rules
inconsistent.
prioritize norms in case both of them becomes applicable
norms that compensate the violation of other norms
• Similar to that of Defeasible Logic

Defeasible Logic (DL)
• Rule-base, without disjunction
r : A(r) → C(r)
where
r is the unique identifier of the rule
A(r) = a1, · · · , an the antecedent of the rule (where ai is a
literal)
→= { →, ⇒, } denotes the type of the rule (→=strict rule,
⇒=defeasible rule, and =defeater)
C(r) the consequent (or head) of the rule
• Classical negation is used in the heads and bodies of rules
Negation-as-failure is NOT used but can be emulated
• Rules may support conflicting conclusions
• Direct Skeptical: conflicting rules do not fire
consistency is preserved
• Priorities on rules (superiority relation) may be used to resolve
some conflicts among rules

Defeasible Logic (cont.)
• Constructive proof theory
• Flexible and computationally eﬃcient
linear w.r.t. the number of literals
• Many extensions and applications
policy-based intention
e-contracts analysis and monitoring
web service composition
. . .

Modal Defeasible Logic (MDL)
• Extension of DL with the support of modal operators

• The language consists of:
a set PROP of propositional atoms
Lit = PROP ∪ { ¬p | p ∈ PROP } represents a set of literals
If q is literal (∼q is its complement)
– if q is a positive literal p, then ∼q is ¬p
– if q is ¬p, then ∼q is p
MOD denotes a set of model operators

• The language consists of:
a set PROP of propositional atoms
Lit = PROP ∪ { ¬p | p ∈ PROP } represents a set of literals
If q is literal (∼q is its complement)
– if q is a positive literal p, then ∼q is ¬p
– if q is ¬p, then ∼q is p
MOD denotes a set of model operators
• Introduced the concept of contrary-to-duty obligation in the
head of the rule
For an expression a ⊗ b, the intuitive reading is that
if a is possible, then a is the ﬁrst choice and b is the second
one;
if ¬a holds, i.e., a is violated, then b is the actual choice.

LegalRuleML to MDL Mapping
• LegalRuleML is inherited from RuleML
i.e., elements related to RuleML can be done using the
mapping provided in (Governatori, 2005)

• LegalRuleML is inherited from RuleML
i.e., elements related to RuleML can be done using the
mapping provided in (Governatori, 2005)
• For instance, the following LegalRuleML code can be
transformed into the literal pay(Purchaser, Supplier)
1 <ruleml:Atom key=":atom109">
2 <ruleml:Rel iri="pay"/>
3 <ruleml:Ind>Purchaser</ruleml:Ind>
4 <ruleml:Ind>Supplier</ruleml:Ind>
5 </ruleml:Atom>

– Statements
Type of Statements in LegalRuleML
StatementsNorm
Statements
Constitutive
Statements
Prescriptive
Statements
Violation-Reparation
Statements
Reparation
Statements
Penalty
Statements
Factual
Statement
Override
Statement

– Statements
Type of Statements in LegalRuleML
StatementsNorm
Statements
Constitutive
Statements
Prescriptive
Statements
Violation-Reparation
Statements
Reparation
Statements
Penalty
Statements
Factual
Statement
Override
Statement
which correspond to DL elements
LegalRuleML DL
Factual Statement Fact
Constitutive Statement Strict rule
Prescriptive Statement Defeasible rule
Override Statement Superiority relation
Violation-Reparation Statement describe later

– Statements
An Example
1 <lrml:PrescriptievStatement key="r1">
2 <ruleml:Rule key=":ruletemplate1">
3 <ruleml:if>
4 <ruleml:And>
6 <ruleml:Rel iri=":specialOrder"/>
7 <ruleml:Ind>X</ruleml:Ind>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
12 <lrml:Obligation>
14 <ruleml:Rel iri=":surcharge"/>
16 </ruleml:Atom>
17 </lrml:Obligation>
18 </ruleml:then>
19 </ruleml:Rule>
20 </lrml:PrescriptievStatement>

– Statements
An Example
3 <ruleml:if>
4 <ruleml:And>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
16 </ruleml:Atom>
18 </ruleml:then>
19 </ruleml:Rule>
rule label r1

– Statements
An Example
3 <ruleml:if>
4 <ruleml:And>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
16 </ruleml:Atom>
18 </ruleml:then>
19 </ruleml:Rule>
rule label r1rule type
defeasible rule

– Statements
An Example
3 <ruleml:if>
4 <ruleml:And>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
16 </ruleml:Atom>
18 </ruleml:then>
19 </ruleml:Rule>
defeasible rule
rule body specialOrder(X)

– Statements
An Example
3 <ruleml:if>
4 <ruleml:And>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
16 </ruleml:Atom>
18 </ruleml:then>
19 </ruleml:Rule>
defeasible rule
rule head OBLsurcharge(X)

– Statements
An Example
3 <ruleml:if>
4 <ruleml:And>
8 </ruleml:Atom>
9 </ruleml:And>
10 </ruleml:if>
11 <ruleml:then>
16 </ruleml:Atom>
18 </ruleml:then>
19 </ruleml:Rule>
defeasible rule
rule head OBLsurcharge(X)
r1 : specialOrder(X) ⇒ OBLsurcharge(X)

– Statements
Some notes:
• Penalty statements is essentially a list of deontic literals that
can be appended to the head of the rule(s) concerned using
⊗-expression based on the key referenced by the
corresponding Reparation statements.

– Statements
Some notes:
• Penalty statements is essentially a list of deontic literals that
can be appended to the head of the rule(s) concerned using
⊗-expression based on the key referenced by the
corresponding Reparation statements.
• The same penalty statement may applies to many diﬀerent
prescriptive statements, as described in the Reparation
statements.

– Other constructs
However,
• Some elements in LegalRuleML are not that intuitive
• For instance, LegalRuleML provides two elements to
determine whether an obligation or a prohibition of an object
has been fulfilled (<lrml:Compliance>) or violated
(<lrml:Violation>)
Definition
• A compliance is an indication that an obligation has been
fulfilled or a prohibition has not been violated.
• A violation is an indication that an obligation or prohibition
has been violated.

– Compliance and Violation
1 <lrml:PrescriptiveStatement key="ps2">
3 <ruleml:if>
4 <ruleml:And key=":and1">
5 <lrml:Violation keyref="#item3"/>
6 <lrml:Permission>
8 <ruleml:Rel iri=":rel1"/>
10 </ruleml:Atom>
11 </lrml:Permission>
12 <lrml:Obligation key="oblig1">
16 </ruleml:Atom>
18 </ruleml:And>
19 </ruleml:if>
20 . . .

3 <ruleml:if>
6 <lrml:Permission>
10 </ruleml:Atom>
16 </ruleml:Atom>
18 </ruleml:And>
19 </ruleml:if>
20 . . .
• need to determine whether
the object with key=item3
has been violated or not

3 <ruleml:if>
6 <lrml:Permission>
10 </ruleml:Atom>
16 </ruleml:Atom>
18 </ruleml:And>
19 </ruleml:if>
20 . . .
• need to determine whether
the object with key=item3
has been violated or not
• Two cases: when item3 is
(i) a literal
(ii) a rule

Case 1 [Element as literal] Assume that p is element
that item3 refers to, from the code above we have:
ps2 : PERrel1, OBLrel2, violate(p) ⇒ C(ps2)

Some observations:
• The case where item3 is a literal is simple. It can be
appended to the body as a precondition to activate the rule
using the table below:
q OBLq FORq
Compliance q OBLq, q FORq, ¬q
Violation ¬q OBLq, ¬q FORq, q

Some observations:
• The case where item3 is a literal is simple. It can be
appended to the body as a precondition to activate the rule
using the table below:
q OBLq FORq
Compliance q OBLq, q FORq, ¬q
Violation ¬q OBLq, ¬q FORq, q
• i.e., if p = OBLq, then the above rule becomes:
ps2 : PERrel1, OBLrel2, OBLq, ¬q ⇒ C(ps2)

Case 2 [Element as Rule] In case of violation, we need to verify
whether referenced rule is either:
• inapplicable such that there a non-provable literal in the
antecedent of the rule

Case 2 [Element as Rule] In case of violation, we need to verify
whether referenced rule is either:
• inapplicable such that there a non-provable literal in the
antecedent of the rule
• the immediate consequents of the rule is defeated or overruled
by a conﬂicting conclusion.

Deﬁnition (Rule Status)
Let D = (F, R, >) be a defeasible theory, let Σ be the language of
D. For every r ∈ Rb, rc denotes the rule referenced by the element
We deﬁne verifyBody(D) = (F, R , > ) where:
R = R Rd ∪ { r+
c : A(rc) ⇒ inf (rc),
−
c : ⇒ ¬inf (rc),
r−
cv : ¬inf (rc) ⇒ violation(rc),
r+
cc : inf (rc), comply(C(rc, 1)) ⇒ compliance(rc),
r+
cv : inf (rc), violate(C(rc, 1)) ⇒ violation(rc),
> => ∪ { r+
c > r−
c }

• For each rc, inf (rc), ¬inf (rc), compliance(rc) and
violation(rc) are new atoms not in the language of the
defeasible theory.

defeasible theory.
• inf (rc) and ¬inf (rc) determine whether a rule is in force.

defeasible theory.
• If rc is in force, then we verify whether:

defeasible theory.
the ﬁrst literal that appears at the head of rc is compliant i.e.,
compliance(rc ) or

defeasible theory.
the ﬁrst literal that appears at the head of rc is compliant i.e.,
compliance(rc ) or
rc is violated i.e., violated(rc )

Conclusions
• We proposed a mapping of legal norms represented using
LegalRuleML into DL

Conclusions
LegalRuleML into DL
• With current LegalRuleML speciﬁcations, strange results
might appear if an element <lrml:violation> (or
<lrml:compliance>) appears at the head of a
statement—additional restrictions are required.

Conclusions
LegalRuleML into DL
• The real impedance is the lack of dedicated and reliable
infrastructure

Conclusions
LegalRuleML into DL
• The real impedance is the lack of dedicated and reliable
infrastructure
• As future work, we are planning to incorporate the presented
approach into some smart-contract enabled systems

Questions?

References
Antoniou, Grigoris et al. (2001). “Representation Results for Defeasible Logic”.
In: ACM Transactions on Computational Logic 2.2, pp. 255–286.
Gordon, Thomas F., Guido Governatori and Antonino Rotolo (2009). “Rules and
Norms: Requirements for Rule Interchange Languages in the Legal Domain”.
In: RuleML’09. Springer Heidelberg, pp. 282–296.
Governatori, Guido (2005). “Representing Business Contracts in RuleML”. In:
International Journal of Cooperative Information Systems 14.2–3, pp. 181–216.
Nute, Donald (2001). “Defeasible logic: Theory, Implementation and
Applications”. In: Proceedings of the 14th International Conference on
Applications of Prolog (INAP 2001). Springer, Berlin, pp. 151–169.

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