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Legal Knowledge and Information Systems
E. Francesconi et al. (Eds.)© 2022 The authors and IOS Press.
This article is published online with Open Access by IOS Press and distributed under the termsof the Creative Commons Attribution Non-Commercial License 4.0 (CC BY-NC 4.0).
doi:10.3233/FAIA220485

Consumer Dispute Resolution System
Based on PROLEG
aShidaka NISHIOKAa,1, Yuto MORI b and Ken SATOHc,1
Japan Advanced Institute of Science and Technology, Japanb
Hitotsubashi University, Japanc
National Institute of Informatics and Sokendai, Japan

Abstract. It is challenging for lay consumers to predict a legal conclusion byapplying appropriate law in a consumer dispute. We developed a system that assists
consumers to predict a possible legal conclusion. The system enables consumers toidentify the type of consumer disputes by using a tree structure, and to apply
appropriate legal rules implemented as PROLEG programs. We arranged the system
to avoid possible inconsistency between the tree structure and the PROLEG program.
Keywords. PROLEG, ISAI PROLEG, PROLEG Menu, Japanese Ultimate Fact
theory, Japanese Consumer Law, Consumer Disputes

1. Introduction
In Japan, disputes between consumers and business operators (“Consumer Disputes”)
are common. Under Japanese consumer law, there are variations in the types ofConsumer Disputes defined by statutes, and applicable legal rules differ depending on
the type. It can be challenging for consumers with no legal knowledge to determine thetypes of Consumer Disputes and to correctly select the applicable legal rules.
Japanese ultimate act theory (yoken-jijitsu-ron in Japanese, the “JUF theory”)
is the legal rules that Japanese courts apply to civil cases. PROLEG is a logic
programming language that can implement JUF theory[1]. The interactive system forarranging issues based on PROLEG (“ISAI PROLEG”)[2] provides a user interface thatallows users to input values representing the facts of cases into variables in PROLEG
programs. PROLEG and ISAI-PROLEG can implement the legal rules of the Japanese
consumer law in the form of JUF theory. However, for consumers to take advantage ofprogrammed legal rules, they must correctly identify the type of Consumer Disputes andselect a PROLEG program implementing the legal rule applicable to the identified type.
We developed Consumer Dispute Resolution System that assists consumers in
identifying types of Consumer Disputes and select applicable PROLEG programs.

2. PROLEG Menu
PROLEG Menu is a software that can implement a tree structure with a user interface.
Each node of the tree can have a question and multiple answer choices for the question.
1

Corresponding Authors: Shidaka Nishioka, shidaka.nishioka@jaist.ac.jp; Ken Satoh, ksatoh@nii.ac.jp

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At each node, a user can select one of the choices through the user interface. The next
node to be reached is determined based on the user’s answer. Each leaf node is associatedwith a PROLEG program in the form of ISAI PROLEG. When the user reaches any ofthe leaf nodes, PROLEG Menu calls the PROLEG program associated with the leaf node.

3. Description of System
The system comprises two parts: Tree and Logic, as shown in Figure 1.

Start
Tree Part

Type A
Type B
Type CType D
Type EPROLEG Program for Type A  UI to accept facts
PROLEG Program for Type B  UI to accept facts
PROLEG Program for Type C  UI to accept factsPROLEG Program for Type D  UI to accept facts
PROLEG Program for Type E  UI to accept facts

Types of Consumer
Disputes identified

Logic PartFigure 1. Functions of Tree and Logic Parts.

3.1. Tree PartThe Tree Part enables a user, typically a lay consumer, to identify the type of Consumer
Disputes and to select the appropriate PROLEG program. We implemented the Tree Part
by using PROLEG Menu such that it has a tree structure. Each node in the tree has aquestion. The user’s answer to the question at a certain node determines which child nodethe user goes to next. By repeating this process, the user reaches one of the leaf nodes.
The questions at each node have been deployed such that the system can identify the typeof Consumer Disputes. Therefore, when the user reaches a leaf node, the type ofConsumer Dispute is identified. Each leaf node was associated with a PROLEG program
which implements the legal rule applicable to the identified type of Consumer Disputes.
3.2. Logic Part
The system transitions to the Logic Part when a PROLEG program is called at the endof the Tree Part. The Logic Part accepts a user’s and a business operator’s factual
assertions and infers the legal conclusion by applying legal rules to those facts. We
implemented the Logic Part by using the ISAI PROLEG such that it has a user interface
that allows users to input the facts they assert. In the Logic Part, the system requests aconsumer and a business operator, the parties to a Consumer Dispute, to input the facts
they want to assert in their Consumer Dispute. After the parties complete inputting, thesystem calculates to reach the legal conclusion inferred by applying the applicable legalrules to the facts input by the parties and displays the results. This enables consumers topredict possible legal conclusions for their Consumer Disputes.

4. Tree Structure for Identifying Types of Consumer Disputes
Generally, each type of Consumer Disputes consists of one or more factors. In the Tree
Part, each node has a question that asks to a consumer if there are facts satisfying one of

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the factors of Consumer Disputes. To identify the types of Consumer Disputes, wedeployed questions about factors common to more types of Consumer Disputes at uppernodes. Questions about factors included only in fewer types of Consumer Disputes areset at lower nodes.
For example, under the Specified Commercial Transactions Act (the “SCTA”)
of Japan, Consumer Disputes can be classified in three types as shown in the table below:
Table 1. Types of Consumer Disputes and Factors in each type of Consumer DisputeTypes
123Consumer
YYYLonger Than 2 Months
YY-

More Than 50,000 YenY-

In the Table 1, “Y” indicates that the type of Consumer Dispute in the sameline has that factor. For example, Consumer Dispute Type 2 has Factors Consumer andLonger Than Two Months. To identify the type of Consumer Dispute, the Tree Part asks
the consumer at the initial node if the case has a fact satisfying the Factor Consumer,
because the Factor Consumer is common to all types. If the consumer answers “no,” thesystem can conclude that the SCTA does not apply to the case. If the consumer answers“yes,” then the Tree Part asks for the sufficiency of the Factor Longer Than Two Months,
because it is common to Type 1 and 2. If the consumer's answer is “no,” the system canconclude that the case is of Type 3. If the consumer's answer is “yes,” the Tree Partfurther asks at the next node whether the Factor More Than 50,000 Yen is satisfied. In
this manner, the Tree Part identifies the type of Consumer Dispute.

5. Avoiding Inconsistencies Between Tree and Logic Parts
Previously, PROLEG programs operate independently, not associated with a tree
structure. On the other hand, in the system, the PROLEG programs in the Logic Part areassociated with the Tree Part where the types of Consumer Disputes are determined byusing a tree structure. Since both factors to identify a type of Consumer Disputes andlegal requirements of applicable legal rules are defined by the Japanese consumer law,in the system, one of the factors to identify the type of Consumer Disputes appearing asa question at a node in the Tree Part can be identical to one of the legal requirements inthe applicable legal rules implemented as a PROLEG program in the Logic Part.
Therefore, an inconsistency may occur between the Tree and Logic Parts.
For example, assume that a Consumer Dispute is of Type 1 in the Table 1,
which has Factors Consumer, Longer Than Two Months and More Than 50,000. Supposethat the applicable legal rule to cancel the contract in Type 1 includes Requirements
Consumer, Telling False and Belief. Here, Consumer appears as a Factor and aRequirement. Previously, the PROLEG program implementing this legal rule must
contain atomic formulae representing all the three Requirements Consumer, Telling
False and Belief with the variables representing the presence or absence of facts thatsatisfy the three Requirements. If the system has this PROLEG program as is in the Logic
Part, a user who answered “yes” to the question asking “are you a consumer?” in theTree Part may input a fact indicating that the user is not a consumer in the Logic Part.
To avoid this inconsistency, we implemented the system such that, if a Factor
in the Tree Part and a Requirement in the Logic Part are identical, the PROLEG programin the Logic Part does not contain that Requirement. For example, in the case of Type 1
above, because the Tree Part asks the presence or absence of Factor Consumer to identifyS. Nishioka et al. / Consumer Dispute Resolution System Based on PROLEG

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the type, the PROLEG program in the Logic Part implementing the applicable legal rule
contains only atomic formulae representing Requirements Telling False and Belief toprevent the user from inputting contradictory facts about Requirement Consumer.
Removal of a certain requirement from the PROLEG programs in this mannerstill maintains the accuracy of the inference for the following reasons. Suppose that, in acertain legal rule, a consumer’s Claim X can be established by the presence of Facts a',b' and c' that satisfy Requirements a, b and c, respectively. This can be expressed in theform of PROLEG as follows:
claim_x(_a', _b', _c') <= requirement_a(_a'), requirement_b(_b'),
requirement_c(_c').
If the consumer answers in the Tree Part that Factor a was satisfied, it meansthat Fact a' exists and the truth value of the atomic formula “requirement_a(_a')” turns
out to be true before the PROLEG program in the Logic Part starts. Based on this premise,the following holds:{claim_x(_a', _b', _c') <= requirement_a(_a'), requirement_b(_b'),
requirement_c(_c').} ҍ requirement_a(_a') ↔ Tя claim_x(_b', _c') <= requirement_b(_b'), requirement_c(_c').
In this manner, the system avoids possible inconsistencies between the Tree andLogic Parts, as shown in Figure 2.
Type X

Yes

Question:
Is factor a satisfied?

factor a is satisfied.

Factors:a, d, e…

Start

PROLEG Program for Type X  UI to accept facts
Requirement a
True
Requirement b
Requirement c
implement

Tree Parta is in common

Logic Part

Legal rule applicable to Type X
Requirements: a, b, cFigure 2. Method to avoid inconsistency between Tree and Logic Parts

6. Conclusion
We demonstrated how the system identifies the types of Consumer Disputes by using atree structure and avoids possible inconsistency between Tree and Logic Parts. In thesemanners, the system assists consumers to predict legal conclusions for Consumer Dispute.
This work was supported by JSPS KAKENHI Grant Numbers, JP17H06103
and JP22H00543.

References[1][2]

Satoh K, et al (2011) Proleg: an implementation of the presupposed ultimate fact theory of Japanese
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Satoh K, et al (2021) Interactive System for Arranging Issues based on PROLEG in Civil Litigation.
Proc. of ICAIL 2021, pp 273 - 274.