A COMPUTATIONAL FRAMEWORK FOR USING BOTH RULES AND PREVIOUSLY-DECIDED CASES IN A LEGAL DECISION MAKING PROCESS UCL KAMALENDU PAL Department of Computer Science University College London Gower Street, London WCIE 6BT A thesis submitted for the degree of Master of Philosophy in the University of London June 1997 / B Ib L . ( l o n o i k .] UNIV., ProQuest Number: U642047 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest U642047 Published by ProQuest LLC(2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 A b stra ct A hybrid knowledge-based system, Advisory Support for Home Settlement in Divorce (ASHSD), which exploits both general legal rules (for rule-based reasoning or RBR) and specific information taken from previously-decided similar cases (for case-based reasoning or CBR), is described. Legal knowledge in the system covers three aspects of matrimonial home settlement in divorce in English law, namely owned home settlement, transfer of tenancy, and injunctions to protect a spouse, or a family member in the custody of a spouse. The user can select either reasoning method (RBR or CBR), or indicate no preference. ASHSD’s rule base consists of two types of rule. The first type of rules determines which options are legally applicable. The second type indicates how the courts are likely to act within the range of options available, which is determined by the first type of rules. When CBR is selected, the system uses the features of previously-decided cases to select the most similar cases to the situation that is described in the input and displays their details of decisions. When no preference is indicated, the system applies each method separately, and then presents results based on an automated relative rating of the qualities of the RBR (based on the second type of rules) and CBR advice. ACKNOWLEDGEMENT It is a great pleasure to acknowledge my debt to many people involved, directly or indirectly, in the completion of this thesis. I am particularly grateful to my supervisors, Professor John Campbell and Dr Mark Levene, for encouraging me in this work, offering suggestions and pruning many unfruitful branches of research. I am grateful to John for his guidance and especially for the time and effort he spent restructuring and making constructive suggestions on early drafts of this thesis. I am grateful to Dr Stephen Guest of the Law Faculty, University College London, for taking time from his busy schedule in the validation study of the implemented system. I am also thankful to Dr Dan Hunter of the Law School, University of Melbourne, Australia, for providing useful comments on the implemented software. It is now my pleasurable duty to record my indebtedness to some of my friends for the help they have given me in producing this thesis. Formost amongst them is Sukhdev Kheb- bal who, over last three years, has given me valuable information on software. Tony Bal- lardie, San jay Kadam, William Langdon, Jens Dzikowski, Rafael Sordini, Eliseo Reategui, Wilfred Ng, Arif Iqbal and Jonathan Poole have provided me with their expert opinions and help. Finally, thanks also go to all members of the Department of Computer Science at UCL for their kind help and cooperation. Contents 1 Introduction 1 1.1 B a c k g ro u n d ............................................................................................................................. 1 1.2 Artificial Intelligence in Context of L a w ..................................................................... 2 1.3 The Legal Theoretical Concepts ...................................................................................... 3 1.3.1 The Legal Positivists ............................................................................................... 4 1.3.2 Legal Realism ............................................................................................................. 8 1.4 The Legal Decision-Making Process ............................................................................... 11 1.5 Model for the Present Research ....................................................................................... 18 1.5.1 Identification and Acquisition of K n o w le d g e .....................................................20 1.5.2 Representation of the Collected K now ledge .....................................................23 1.5.3 Reasoning on the Represented Knowledge ........................................................ 24 1.5.4 Notion of Rule-Based R easoning .......................................................................... 25 1.5.5 Notion of Case-Based Reasoning .......................................................................... 29 1.6 Subject Area of the Research.............................................................................................. 30 C on ten ts iii 1.6.1 Project Orientation ................................................................................................... 31 1.6.2 Why a Hybrid System? ................................................................................................ 32 1.6.3 Overview of A SH SD ................................................................................................... 33 1.7 Structure of the Thesis............................................................................................................ 37 2 Previous Related Research 39 2.1 Introduction ..................................................................................................................................39 2.2 Rule-Based Reasoning System s ............................................................................................ 40 2.2.1 TAXMAN I P roject ................................................................................................... 40 2.2.2 B ritish N ationality A ct ...........................................................................................41 2.2.3 The Oxford Project ................................................................................................... 45 2.2.4 LDS and SAL Systems ................................................................................................46 2.2.5 TAXADVISOR .............................................................................................................. 47 2.2.6 Latent Damage System .................................................................................................47 2.2.7 The Use of Meta-rules in Rule-Based Legal Computer Systems . 48 2.2.8 Commentary on RBR System s ..............................................................................48 2.3 Case-Based Reasoning System s ............................................................................................ 49 2.3.1 JUDGE .............................................................................................................................49 2.3.2 H Y P O ................................................................................................................................ 51 2.3.3 The Trademark Reasoning and Retrieval System (TR2S) ..........................52 Contents iv 2.3.4 CHASER ......................................................................................................................... 53 2.3.5 Commentary on CBR System s ................................................................................54 2.4 Hybrid Legal Knowledge-Based System s ..........................................................................55 2.4.1 TAXMAN I I .................................................................................................................. 55 2.4.2 Gardner’s System ........................................................................................................... 56 2.4.3 GREBE .............................................................................................................................57 2.4.4 CABARET ......................................................................................................................58 2.4.5 PROLEXS ......................................................................................................................60 2.4.6 IKBALS I I ......................................................................................................................61 2.4.7 H ELIC I I ..........................................................................................................................61 2.4.8 Conclusions ...................................................................................................................... 62 3 Framework of the System 64 3.1 Introduction .................................................................................................................................... 64 3.2 Concepts behind ASHSD .......................................................................................... 65 3.2.1 Characterisation ........................................................................................................... 65 3.2.2 Objectives for the System