1. Master Thesis Kick-Off: Extraction of Legal Term Definitions from German Statutory Texts and Court Decisions
Fabian Thomas,

2. Key Facts
Title: Extraction of Legal Term Definitions from German Statutory Texts and Court Decisions
Author: Fabian Thomas
Advisor: M.Sc. Ingo Glaser
Supervisor: Prof. Dr. Florian Matthes
Start: July 1st, 2019
End: December 30th, 2019
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3. Outline Legal theory background Motivation Approach Research Questions
How can legal definitions be identified from statutory texts and court decisions using rule-based approaches?
How can the definitional relevance of legal statements in statutory texts and court decisions be determined?
Timetable
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4. Legal theory background
Subsumption
Description of Facts
Implies?
Legal consequence
Imply
Directs search for
Legal norms
Consist of
Legal norms
Consist of
Interpretation
Legal norms
Legal norms
Characteristics
Legal terms
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5. Legal theory background
Definite and indefinite legal terms
Definite
Defined by legal definitions in statutory texts
Indefinite
Not explicitly defined
Leave (purposely) much more room for interpretation
May be defined by laws of nature or common sense
Often depend on further specification by court decisions
Continuous spectrum between definite and indefinite terms
Terms most often lack a clear legal definition
Still specified to some extent inside the statutory texts
Other sources of information for term interpretation
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6. Legal theory background
Definition specifications
Both definite and indefinite legal terms are often further specified in other norms or court decisions
Examples:
Legal definition (§ 2 LandesbauO NRW):
… (2) Gebäude sind selbständig benutzbare, überdeckte bauliche Anlagen, die von Menschen betreten werden können und geeignet oder bestimmt sind, dem Schutz von Menschen, Tieren oder Sachen zu dienen. …
Specification from a court decision (BFH, March 25th 1977):
... (1) Bewertungsrechtlich ist ein Bauwerk als Gebäude anzusehen, wenn es […] fest mit dem Grund und Boden verbunden ist.
(2) Das ist der Fall, wenn […] Fundamente vorhanden sind, das Bauwerk auf diese gegründet und dadurch mit dem Boden verankert ist. ….
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7. Legal theory background
Sources of information for legal term interpretation
Meaning in common language
Purpose of the law
History of the law‘s origins
Legal definitions
Auxiliary norms which elaborate on the legal definition
General use of the term in this and other legal contexts
Interpretation of the term in court decisions
Focus of this work
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8. Motivation User perspective
To apply legal norms a lawyer or judge has to …
Identify all contained legal terms
Find legal definitions for every term
Find all norms which elaborate on these legal definitions or are otherwise relevant for understanding
Get an overview of the use of every term inside the law and other laws
Find definitions and specifications in court decisions
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9. Motivation Problems with legal term research
Legal definitions are realised in various ways
Elaborating information lacks a consistent structure
Legal definitions and other relevant norms may be scattered across the law text
Scope of a legal definition may span across different laws and is hard to overview
Information contained in only one norm or court decision may be deciding for a legal case
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10. Approach Solution steps
Extract legal definitions from statutory texts and court decisions
Determine the definition scope (statutory texts and related court decisions)
Find all legal statements containing the term to provide a full overview and assign them to the respective definition scope
Rank legal statements by their definitional relevance
Extracted definitions and ranked term instances can be used to
Automatically annotate the legal texts with relevant information
Summarize and structure legal definitions in a consistent way
Improve search results
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11. Term instance retrieval
Approach
System conception
Text
Text
Indexing
Indexed DB
Statutory texts
Court decisions
Data
Analysis
Annotation
Analysis
Training data
Rules
Rules
Definition extraction
(RQ1)
Term instance retrieval
Definite l.t.
Ranking model
Legal definitions
Indefinite l.t.
Term instances + context
Ranked term instances
User
Term instance ranking (RQ2)
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12. Research Questions
RQ1: How can definitions be identified using rule-based approaches?
Structure of legal definitions
Most legal definitions follow a limited set of rules, e.g.:
Approach
Regular expressions and grammatical rules
Building upon previous work of rule-based definition extraction
Exceptions to the defined rules will be covered in RQ2
Bracket terms
Die Ehegatten sollen einen gemeinsamen Familiennamen (Ehenamen) bestimmen.
Copula structures
Sachen im Sinne des Gesetzes sind nur körperliche Gegenstände.
Definitional lists
Im Sinne dieses Gesetzes sind
1.    Pflanzenschutz: …
[…]
3.    Pflanzen: …
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13. Research Questions
RQ1: How can definitions be identified using rule-based approaches?
Determining definition scope
Legal definitions can be valid inside
A single law
Multiple laws
A whole legal domain
Legal definitions can be explicitly “borrowed” from another law by referencing the definition
Solution approaches:
Identifying signal key words (e.g. “im Sinne dieses Gesetzes”)
Analysing norm reference structure
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14. Research Questions
RQ1: How can definitions be identified using rule-based approaches?
Sub-Questions
RQ1.1: What different types of legal definitions exist?
RQ1.2: What types of legal definitions are suitable for rule-based extraction?
RQ1.3: How effective are rule-based approaches for definition extraction applied to the German federal statutory and court decision corpus?
RQ1.4: What are suitable methods for determining the scope of legal definitions?
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15. Research Questions
RQ2: How can the definitional relevance of legal statements be determined?
What is definitional relevance?
Term instances can be especially relevant if the containing legal statement …
falls out of the rule-based definition extraction, but has definitional characteristics
explictly extends or limits an existing definition
is dependent of another norm for its validity
has a generalization level which allows for application in many legal cases
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16. Research Questions
RQ2: How can the definitional relevance of legal statements be determined?
Existing work
Court decisions
Extensive formalization and categorization schemes for definitions and elaborating statements
Definition of a large set of linguistic features which indicate definitions
Classification (Naive Bayes, kNN, NBTree etc.) and ranking using a regression model
Statutory texts
Classification schemes for functional types of legal norms
Semantic classification of legal norm sentences (duty, prohibition, definition etc.) using linguistic feature extraction and ML models
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17. Research Questions
RQ2: How can the definitional relevance of legal statements be determined?
Sub-Questions
RQ2.2: How can elaborating legal statements in statutory texts and court decisions be categorized?
RQ2.3: What are suitable methods for determining definitional relevance of a legal statement?
RQ2.4: How can existing ranking methods for legal statements in court decisions be improved?
RQ2.5: How effective are the proposed ranking approaches applied to the German federal statutory corpus?
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18. Design & Implementation
Timeline
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Literature Research
Design & Implementation
Evaluation
Writing
Review
Start Date
Kickoff
Submission
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19. Fabian Thomas
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20. References
Glaser, I., Scepankova, E., & Matthes, F. (2018). Classifying semantic types of legal sentences: Portability of machine learning models. Frontiers in Artificial Intelligence and Applications, 313, 61–70. Waltl, B., Muhr, J., Glaser, I., Bonczek, G., Scepankova, E., & Matthes, F. (2017). Classifying legal norms with active machine learning. Frontiers in Artificial Intelligence and Applications, 302, 11–20. Waltl, B., Bonczek, G., Scepankova, E., & Matthes, F. (2019). Semantic types of legal norms in German laws: classification and analysis using local linear explanations. Artificial Intelligence and Law, 27(1), 43–71. Waltl, B., Matthes, F., Waltl, T., & Grass, T. (2016). LEXIA: a data science environment for Semantic analysis of German legal texts. Walter, S. (2010). Definitionsextraktion aus Urteilstexten.
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