Content uploaded by Pepijn R. S. Visser
Author content
All content in this area was uploaded by Pepijn R. S. Visser on Aug 08, 2014
Content may be subject to copyright.
Legal knowledge based systems
JURIX 91
Model-based legal reasoning
The Foundation for Legal Knowledge Systems
Editors:
J.A.P.J. Breuker
R.V. De Mulder
J.C. Hage
P.R.S. Visser, R.W. Van Kralingen, Reasoning about definitions in statutes: J.A.P.J.
Breuker, R.V. De Mulder, J.C. Hage (eds.), Legal knowledge based systems JURIX 91:
Model-based legal reasoning , The Foundation for Legal Knowledge Systems, Lelystad:
Koninklijke Vermande, pp. 113-122, 1991 ISBN 90 6040 989 2.
More information about the JURIX foundation and its activities can be obtained by
contacting the JURIX secretariat:
Mr. C.N.J. de Vey Mestdagh
University of Groningen, Faculty of Law
Oude Kijk in 't Jatstraat 26
P.O. Box 716
9700 AS Groningen
Tel: +31 50 3635790/5433
Fax: +31 50 3635603
Email: sesam@rechten.rug.nl
1991 JURIX The Foundation for Legal Knowledge Systems
http://jurix.bsk.utwente.nl/
REASONING ABOUT DEFINITIONS IN STATUTES
P.R.S. Visser and R.W. van Kralingen
Department of Law and Computer Science
Faculty of Law, University of Leiden
Hugo de Grootstraat 32
P.O. Box 9521
2300 RA Leiden
The Netherlands
Summary
The formalization of texts of law entails the analysis of its structure. Often, the
structure is modified and (parts of) legal norms are reformulated on an ad hoc basis, to
suit the selected representation method. A theory about coherence in law can serve as a
basis to extract and represent knowledge about the structure of texts of law. This
knowledge can be used to reason about separate text elements, thus making it possible
to preserve the structure of these texts. As we will show, meta-level reasoning is
needed to deal with conflicts that arise if the structure of the statute is preserved. In this
paper, we concentrate on reasoning about definitions.
1. Introduction
Statute-based-legal-knowledge systems employ formalized models of texts of law to
conduct reasoning processes. The formalization process often reveals relations within
and between legal texts not explicitly present in the statute text. This circumstance
necessitates an extensive interpretation during the formalization process, often yielding
intertwined images of parts of the statute's texts. The resulting formal representations
are often difficult to survey.
A possible solution to this problem is a formal representation that leaves the implicit
relations out of consideration and concentrates on the direct formalization of elements
of the texts of law. However, since reasoning with statutes largely depends on the
relations between text elements, it is imperative to have a representation formalism and
a reasoning mechanism that can deal with coherence. As we will show, this approach
implies the use of meta-level reasoning.
In this paper we describe part of a framework for dealing with coherence in law. We
depart from the theoretical framework provided by Brouwer (1990). This framework
facilitates the mapping of different text elements onto an abstract model of a legal
norm. This mapping enables us to dissociate conclusions from the underlying rules,
thus making it possible to use these abstract conclusions further on in the reasoning
process. The approach necessitates reasoning with text elements as well as reasoning
about relations between these elements. Only a limited part of the framework, namely
reasoning with and about definitions in statutes, is elaborated (these definitions
constitute parts of norms). In the next chapter we outline the framework.
113
2. Coherence in law
Brouwer (1990) argues that in order to elucidate the notion of coherence, two sorts of
elements must be distinguished: those that appear in the texts of law, such as chapters
and sections, and those that can be regarded as legal norms. The structure of texts of
law is generally not the same as the structure of the law seen as a collection of norms
(Brouwer, 1990, p.5). However, if we accept the proposition that law consists of
norms, it must be possible to map the texts of law onto a collection of norms
(Brouwer's argument not only concerns texts of law, but also other sources of law).
The formalization of texts of law entails the analysis of the structure of these texts.
Often, during the formalization, the structure is modified and (parts of) legal norms are
reconstructed on an ad hoc basis, to suit the selected representation method. In the JURI-
CAS system (De Mulder et al., 1989) this procedure has resulted in a criss-cross of rela-
tions between the texts of law and the formal rules reflecting the norms contained in
these texts. In the TESSEC system, it has been tried to preserve the structure of the
statute texts. However, Nieuwenhuis has neither been able to preserve a direct corres-
pondence between the statute texts and the formal rules. In his formal rules he
incorporates exceptions as conditions in rules, thus losing the exceptions as separate
elements of the statute text (Nieuwenhuis, 1989, pp.193-197).
The designers of JURICAS and TESSEC do not report to have used a theory about coher-
ence in law. Such a theory could serve as a basis to extract and represent knowledge
about coherence in law, thus making it possible to preserve the structure of a statute
texts as well. Before going into some of the possibilities this approach has to offer, we
discuss the theory about coherence in law as formulated by Brouwer (1990).
2.1. Legal norms
What is a legal norm? Von Wright (1983) defines a norm as 'a statement to the effect
that something ought to or may or must not be done'. This definition denotes a
diversity of norms. In the legal domain, Brouwer claims that the concept legal norm
covers four different types of norms:
•Duty-imposing norms: duty-imposing norms determine what types of
conduct constitute actionable wrongs. They impose duties on persons to
abstain from such conduct, or they impose obligations on persons to perform a
specified conduct (Hart, 1961). An instance of a duty-imposing norm is the
obligation of employees to sign in at an employment exchange if they become
unemployed.
•Permissive norms: permissive norms grant persons the right to act or to
refrain from acting. If we take the adage 'everything that is not forbidden, is
allowed' to be true, permissive norms do not have an independent function.
However, there are sufficient reasons to consider the 'permissive norms' an
independent category. An instance of such a reason is the possibility of a
conflict in a norm-hierarchy (Brouwer, 1990) (e.g. an explicit permission
issued by the central government cannot be restricted by regulations issued by
government institutions lower in the hierarchy).
•Power-conferring norms: power-conferring norms provide individuals (or
institutions) with facilities to realize their goals. Power-conferring norms
provide facilities to create structures of rights and duties within the coercive
114
framework of law (Hart, 1961 p. 27; cf. Brouwer, 1990). An instance of a
power-conferring norm is the norm providing the Dutch Minister for Social
Services and Employment with the right to label someone as an employer.
•Norms of adjudication: norms of adjudication are defined as norms that
regulate the authoritative determination of the question whether a duty-impos-
ing or power-conferring norm has been broken as well as the legal
consequences thereof. They may be of the duty-imposing, permissive and even
power-conferring kind. (Brouwer, 1990; Hart, 1961). An instance of a norm
of adjudication is the norm granting the Industrial Insurance Board the right to
cut back on social security benefits in certain specified cases.
2.2. Properties of legal norms
A norm must have certain properties to fall within the definition given in the previous
chapter. Brouwer (1990) (cf. Von Wright, 1983) mentions five properties that
correspond to as many questions:
•The description of the norm subject (who is obliged or allowed to act?).
•The description of the act (what must be done or left undone?).
•The deontic modality (is there an obligation or a permission to act or to refrain
from acting?).
•The description of the place of the act (where must or may the act take place?).
•The description of the time of the act (when must or may the act take place?).
A norm that comprises these elements is a complete norm. A complete norm is a
theoretical construct and does not appear as such in the legal sources. The theoretical
model of a complete norm forms the basis for Brouwer's theory about the structure or
coherence in law.
The miscellaneous elements of complete norms are distributed over the texts of law. In
their mutual coherence these texts express a (collection of) norms. The core of a norm
(the description of the norm subject, the act and the deontic modality) is often
represented in one section. This section can serve as a root for the reasoning process.
Other elements of the norm can often be found in other sections. Definitions, for
instance, being part of different norms, are often placed under separate headings (e.g.
in chapters containing general provisions). If we start the reasoning process at the core
of the norm we can extend this root to include all remaining text elements relevant to
the norm.
In this paper we restrict ourselves to duty-imposing norms. We illustrate the
applicability of the Brouwer framework and of some of the reasoning techniques
needed to reach conclusions about these norms with the help of examples originating
from the Dutch Unemployment Act.
3. The Dutch Unemployment Act
We deem the Dutch Unemployment Act a fitting domain for application of the
framework we have introduced in chapter 2. The structure of the statute is as follows:
the statute comprises eleven chapters. The first chapter of the statute contains general
sections. In this chapter several notions used elsewhere in the statute are defined (e.g.,
employer, employee, employer-employee relationship, pay). Chapter two of the statute
deals with the compulsory unemployment insurance. It starts with
115
some general sections that address unemployment, the right to unemployment benefits,
etc.
The sections 24, 25 and 26 form the core of the Unemployment Act; they lay down the
rules (duties) employees have to comply with in order to realize their rights to unem-
ployment benefits. Chapter two further contains some sections about procedural
aspects of the payment of unemployment benefits, duration of the benefits, etc. In the
remainder of the statute diverse subjects are dealt with, such as the voluntary unemploy-
ment insurance (chapter three), finance of the act (chapter seven), implementing bodies
(chapter eight) and penalty clauses (chapter eleven).
3.1. Section 24 of the Unemployment Act
Section 24 of the Unemployment Act contains some obligations an employee has to
meet in order to realize his right to unemployment benefits. If an employee fails to
comply with one of these obligations his benefits can be docked. Paragraph one of the
section can be translated as follows:
Section 24 paragraph 1
The employee avoids:
a. becoming culpably unemployed;
b. being or remaining unemployed as a result of;
1. insufficiently trying to obtain commensurate work;
2. failing to accept commensurate work or failing to acquire commensurate
work through his own fault;
3. failing to keep commensurate work through his own fault; or
4. having job-related demands that hinder the acceptance or obtention of
commensurate work;
c. not receiving benefits as indicated in section 19, paragraph 1, items a, b, c, or
d because of any act or abstention that he can reasonably be blamed for.
Paragraph 1 of section 24 comprises the cores of at least six duty-imposing norms (it is
a compound norm), namely: paragraph 1 item a, paragraph 1 item b 1°, paragraph 1
item b 2°, paragraph 1 item b 3°, paragraph 1 item b 4°, and paragraph 1 item c
(paragraph 1 item b 2° and paragraph 1 item b 4° can be split further). The paragraph
contains a single norm subject (the employee), descriptions of the acts (items a, b and
c) and a single deontic modality (avoids). It does not accommodate any information
about the places of the acts or the times of the acts.
3.2. Reasoning about norms
The first norm contained in section 24 reads: 'the employee avoids becoming culpably
unemployed'. Section 27 of the statute links a sanction to the breach of this norm
(section 27 paragraph 1 reads: 'if an employee fails to comply with one of the
obligations laid down in the sections 24, 25 and 26 ...'). The application of section 27
requires information about the compliance with norms laid down elsewhere in the
Unemployment Act; an abstract conclusion about the duty-imposing norms (has the
norm been breached or not) contained in the sections 24, 25 and 26 is needed to be
able to apply section 27. Abstract conclusions about norms or definitions are often
used as conditions in other rules. We will refer to these abstract conclusions about
norms or definitions as meta-level conclusions.
To reach a conclusion about whether a duty-imposing norm has been breached or not,
one has to reason about the conditions related to the norm. In the following
116
section we elaborate on one condition of the norm of which the core is represented in
section 24 paragraph 1 item a. Since the Unemployment Act grants the right to
unemployment benefits to employees, we have chosen to elaborate the question 'is the
person involved an employee?' ('Right to unemployment benefits' is a concept defined
in the sections 17 to 21 of the Act. The concept 'employee' is used in the definition.).
4. Representation of texts of law
Our representation has the following characteristics. First, the representation is chosen
to preserve the relations between the text elements as much as possible (we elaborate
the idea of multi-layered structures (c.f. Routen, 1989)). A consequence of this
approach is that all text elements referred to in other text elements must be addressable
in the formalized version. The normal indexing mechanism used in statutes (e.g.,
chapters, sections) is extended to be able to refer to sentences as well. Elements that
are addressable in the formalized version are called addressable units.
The second characteristic is related to the first: all conclusions based on the represented
texts of law are linked to addressable units. This makes it possible to distinguish, for
instance between an employee according to section 3 paragraph 1 and an employee
according to section 3 paragraph 3. This facility is used to discriminate between
(possibly contradictory) conclusions reached on the basis of different formalized text
elements (meta-level reasoning).
As a third characteristic, we mention that the formalized text elements are expressed as
predicate-logical rules.
Because the representation does not integrate several sections in one logical rule, the
translation from section to formal rule is relatively straightforward. A section defining
a notion can be translated without explicitly referring to exceptions to its contents made
elsewhere in the statute. This contributes to an important aim of our approach, namely
the decrease of the amount of interpretation needed to translate the texts of law into
logical rules.
Another advantage arises as a result of the need to reason at meta level. As can be seen
in the next chapter, meta-level reasoning necessitates elicitation of knowledge that
remains implicit in several other approaches. Because this kind of knowledge is only
used at meta level this knowledge is stored separately from the formalized texts of law.
To illustrate the representation formalism we present three examples of translations of
texts of law. The first example is part of a section that defines the notion employee. We
will refer to this as an affirmative statement because the statement affirms a person to
be an employee. An example of an affirmative statement can be found in section 3
paragraph 1 of the Unemployment Act. This paragraph reads:
'Employee is the natural person, under the age of 65, having an employer-
employee relationship, according either to private law or to public law.'
The statement is translated into (the consequent of the following rule must be read as
'according to section 3 paragraph 1, person is an employee in the employment of
employer'):
117
Employee (sec_3_par_1, employer, person)
Natural_person (person)
Under_the_age_of (person, 65)
(Private_law_employer_employee_relationship (employer, person)
Public_law_employer_employee_relationship (employer, person)
)
Besides affirmative statements we recognize negative statements. A negative statement
is a statement that potentially negates a conclusion drawn by another statement. By
representing negative statements separately, we maintain a direct correspondence
between the original texts and the formalization (cf. Sartor, 1991). The formalization is
chosen to avert logical contradictions, thereby making it possible to concurrently
confirm an affirmative statement and a negative statement about the same notion. If
such a conflict occurs, it is resolved at meta level. Section 3 paragraph 2 of the Unem-
ployment Act is a negative statement:
'Whoever fulfils his employer-employee relationship outside of the
Netherlands, is not an employee, unless he lives in the Netherlands and his
employer lives or resides in the Netherlands.'
The statement translates:
Not_an_employee (sec_3_par_2, employer, person)
Fulfils_employer_employee_relationship_outside_the_Netherlands (employer,
person)
¬ ( Lives_in_the_Netherlands (person)
(Lives_in_the_Netherlands (employer)
Resides_in_the_Netherlands (employer)
)
)
The last type of statement we mention is a statement restricting the applicability. Such a
statement potentially withholds another statement from being applicable. Note that a
statement restricting the applicability of another statement differs from a negative
statement. Consider an affirmative statement indicating someone is an employee. If a
more specific statement indicates the same person is not an employee, the latter
prevails. Thus the conclusion must be the person is not an employee.
If the negative statement in this example would have been a statement restricting the
applicability, it would be impossible to reach a conclusion. The conclusion the man is
an employee can not be drawn, but neither can we conclude the man not to be an
employee. The difference being the conclusion 'the other statement is not applicable' is
a statement about another statement instead of a statement about a definition. There-
fore, the conclusion is a meta-level conclusion. We will go into this in more detail in
the next chapter. A good example of a statement restricting the applicability can be
found in the Unemployment Act section 4 paragraph 2 (the example concerns a
statement restricting the applicability of a statement defining an employer-employee
relationship):
118
'The first paragraph, items a and b do not apply if the agreement referred to in
item a has been entered into with a natural person on behalf of his personal
affairs.'
The translation of this section is (the conclusion is bold to distinguish it from object-
level conclusions, the consequent of the rule must be read as 'according to section 4
paragraph 2, section 4 paragraph 1 item a and section 4 paragraph 1 item b do not
apply'):
Not_applicable (sec_4_par_2, sec_4_par_1a_and_sec_4_par_1b)
Natural_person (employer)
Agreement (sec_4_par_1a, employer, employee)
Agreement_on_behalf_of_personal_affairs (sec_4_par_2, employer,
employee)
Note that the condition Agreement has a reference to section 4 paragraph 1 item a. This
must be read as: 'an agreement as referred to in section 4 paragraph 1 item a'.
The translated text elements potentially contradict each other with respect to the notion
employee. To be able to draw a conclusion, meta-level reasoning is necessary to solve
this conflict by deciding which rule has priority (here: is the person an employee or is
he not?). In the next chapter we discuss these conflict-resolution mechanisms.
5. Meta-level reasoning
In this section two types of meta-level reasoning will be discussed. The first is
reasoning about text elements with contradictory conclusions (§ 5.2). This type of
reasoning can be seen as a special case of preferring the most specific argument (cf.
Prakken, 1991). The second type is reasoning about explicit restrictions on the
applicability of text elements (§ 5.3). Before we discuss meta-level reasoning, we
distinguish between object- and meta-level reasoning (§ 5.1).
5.1. Separating object level and meta level
The knowledge used to reason with texts of law will be divided into object-level
knowledge and meta-level knowledge. At the object level all texts of law are represent-
ed. As said previously, the representation preserves the implicit and explicit references
to other text elements. The meta level is used to reason about the text elements
represented at object level. The knowledge used for this reasoning is not explicitly
available in the texts of law. Moreover, this knowledge often remains implicit in
human reasoning processes. An example of this kind of knowledge is: an exception
has priority over a general section. These implicit links between several sections related
to one notion are made explicit at the meta level (cf. Breuker and den Haan, 1991).
Related to the meta-level function of dealing with contradictions at the object level,
another function of the meta level is to make abstractions from object-level
conclusions. This is necessary because conclusions at object level are always linked to
an addressable unit. If all text elements related to a certain notion are examined, an
abstract conclusion can be drawn. Typical examples of these abstractions are: (1) the
person is an employee as indicated in section 3 because the person is an employee as
indicated in section 3 paragraph 3, and (2) the person is an employee because the
person is an employee as indicated in section 3. It is the abstract conclusion that is
119
referred to in other (object-level) statements (these abstract conclusions are made
available at the object level by downward reflection (cf. Brumsen et al., 1990)). We
point out that a text element sometimes refers to a conclusion which is not abstract (in
chapter 4 we have used the example 'an agreement as referred to in section 4 paragraph
1, item a').
5.2. Reasoning about text elements with contradictory conclusions
As can be seen we are not able to draw the conclusion that a man is an employee until
all text elements dealing with the definition of the notion employee, have been exam-
ined. At least we have to know if the statements that have not been examined yet,
potentially affect the conclusion so far. To express that a statement potentially affirms a
notion we use the meta-level predicate Affirmative_statement. To express that a
statement potentially rejects a certain notion we use the meta-level predicate Negati-
ve_statement. Below we list predicates with respect to the notion employee (in the
Unemployment Act more statements are relevant to the notion employee).
Affirmative_statement (employee, sec_3_par_1)
Affirmative_statement (employee, sec_3_par_3)
Negative_statement (employee, sec_3_par_2)
When trying to confirm someone is an employee, reasoning starts with an affirmative
statement. If such a statement can be confirmed, a negative statement for the same
notion is searched for and conformation is pursued. If this succeeds, a conflict results
(the conflict does not have to be a problem in a legal sense). If a negative statement can
be found in which an exception is stated to a general (affirmative) rule it is clear that the
exception prevails over the general rule. We consider this kind of reasoning as
reasoning with the meta-level criterion: preferring the most specific argument. We want
to make the meta-level knowledge used for this decision explicit. To express one
statement prevails over another because the latter is more specific, we use the meta-
level predicate More_specific. Below we list these relations with respect to section
3.
More_specific (sec_3_par_2, sec_3_par_1)
More_specific (sec_3_par_3, sec_3_par_2)
Thus, relations concerning specificity are represented explicitly (this can be contrasted
to the approach proposed by Prakken, (1991) who infers these relations from the state-
ments themselves). The relations are used to discriminate between two text elements by
giving the first section priority over the second.
5.3. Reasoning about explicit restrictions on the applicability of text elements
Section 4 paragraph 1 (items a and b) of the Unemployment Act defines two types of
employer-employee relationships. Paragraph 2 of the same section states that under
certain conditions, paragraphs 1 item a and b are not applicable. In case both paragraph
1 item a (or b) and paragraph 2 are confirmed, a conflict situation is reached. The
conclusion based on the first paragraph must be abrogated to solve this conflict. This is
done at meta level, using
the already introduced meta-level predicate Not_applicable (see: section 4). As we
have seen, section 2 leads to the conclusion Not_applicable (sec_4_par_2,
sec_4_par_1a_and_sec_4_par_1b). Before this conclusion can be used it is split up in
its two subconclusions: Not_applicable (sec_4_par_2, sec_4_par_1a) and
120
Not_applicable (sec_4_par_2, sec_4_par_1b). These predicates are used to abrogate
conclusions derived earlier. In the reasoning process, only the conclusions for which
no applicability restrictions are derived will be forward.
6. Conclusions and future research
The framework proposed by Brouwer can be used to reason about text elements at
different levels. At the highest level of abstraction we can reason about norms. On
lower abstraction levels we can reason about separate text elements that constitute these
norms (e.g. definitions). The use of explicit knowledge about the structure of statutes
(meta-level knowledge) enables us to reason about separate text elements. This makes
it possible to leave the structure of texts of law intact, thus simplifying the
formalization of the text elements. This, in turn, improves the readability and maintain-
ability of the knowledge base.
Furthermore, the framework offers opportunities to integrate other legal sources (such
as cases and government directives) in the reasoning process. The possibility to reason
about priorities of norm elements (meta-level reasoning) enables us to reason about
elements of norms contained in other legal sources as well.
Future research will concentrate on other types of meta-level reasoning. More
specifically, we will concentrate on meta-level reasoning about different norm types
and on the integration of norm elements from various legal sources. An experiment
will be staged to implement the presented ideas in the DESIRE specification framework
(Kowalczyk and Treur, 1990).
7. Acknowledgements
This research has been made possible with financial support of the Netherlands
Foundation for the Study of Law (NESRO) acknowledged by the Netherlands
Organization for Scientific Research (NWO), project number 410-203-009.
8. References
Breuker, J., N. den Haan (1991). Separating world and regulation knowledge: where
is the logic. Proceedings of the Third International Conference on Artificial Intelligence
and Law, pp.92-97, Oxford, England.
Brouwer, P.W. (1990). Samenhang in recht; een analytische studie (Coherence in law;
an analytical study). Rechtswetenschappelijke reeks, Wolters Noordhof, Groningen.
Brumsen, H., J. Pannekeet, J. Treur (1990). Modelling Dynamic Aspects of Design
Processes, Vrije Universiteit Amsterdam, report IR-233.
Hart, H.L.A. (1961). The concept of law. Clarendon Law Series, Oxford University
Press, Oxford (Ninth impression, 1978).
Kowalczyk, W. and J. Treur (1990). On the use of a formalized generic task model in
knowledge aquisition. Current trends in Knowledge Acquisition. pp.198-221, IOS
Press.
121
Mulder, R.V. de, C. van Noortwijk and H.O. Kerkmeester (1989). Knowledge
Systems and Law - The JURICAS Project. in: Martino, A.A. (ed.), Pre-proceedings of
the third International Conference on Logica, Informatica, Diritto, Florence, Vol I.
Nieuwenhuis, M.A. (1989). Tessec: een expertsysteem voor de Algemene
Bijstandswet, Kluwer, Deventer.
Prakken, H. (1991). A tool in modelling disagreement in law: preferring the most
specific argument. Proceedings of the Third International Conference on Artificial
Intelligence & Law, pp.165-174, Oxford, England.
Routen, T.W. (1989). Hierarchically Organised Formalisations. Proceedings of the
Second International Conference on Artificial Intelligence and Law, pp.242-250,
Vancouver, Canada.
Sartor, G. (1991). The Structure of Norm Conditions and Nonmonotonic Reasoning
in Law. Proceedings of the Third International Conference on Artificial Intelligence &
Law, pp.155-164, Oxford, England.
Wright, G.H. von (1983). Practical Reason. Philosophical papers, Volume I. Basil
Blackwell, Oxford.
122