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1 J.L. & Inf. Sci. 131 (1981-1983)
The Use of Citation Vectors for Legal Information Retrieval

handle is hein.journals/jlinfos1 and id is 147 raw text is: Vol. 1 No. 2 THE USE OF CITATION VECTORS FOR LEGAL INFORMATION RETRIEVAL C. TAPPER Colin Tapper is one of the founders of the study of computers and law in England, and this paper adds to his contributions to the field. As its title indicates, the article is concerned with the use of case citations as selection vectors in legal information retrieval, and, in particular, with the value of citation vestors in comparison to the usual semantic vectors currently used. The author details recent experiments with citation vectors in the United States and at the Norwegian Research Centre for Computers and Law (NRCCL). The comparative results of using citation vectors against semantic vectors in these experiments are documented and considered, and Mr. Tapper provides some valuable discussion of the algorithms used in computing and assessing vectors in data retrieval. Despite the complexity of this work, it will be of great value to all interested in the field of computers and law, because of its implications for the future development of legal data retrieval. The first section of this article is intended for those who have no, or little, previous awareness of legal information retrieval techniques. Since the main aim of the article is to explain the theory behind the substitution for such methods of citation vectors those who have the requisite familiarity with matching and vector based systems as applied to law might prefer to start with the second section. 1. Current Legal Information Retrieval Techniques It is now about 25 years since at the University of Pittsburgh in Pennsylvania Professor John Horty first succeeded in applying computerised methods to the retrieval of legal information. It is a tribute to his insight that the techniques which he devised remain the bedrock of virtually all of the systems which operate in the world today. The essence of the technique is the identification in the text of a document of a word, or words, in a particular combination which have been selected by the lawyer as being likely to indicate the relevance of that document to the lawyer's problem. As normally implemented the system creates a concordance of the full legal texts constituting the database of the system, excluding only words of such low prima facie information content that they are highly unlikely to be nominated by lawyers as search terms. Each concordance item then becomes a potential search term, and searches are typically conducted by the nomination of classes of words, for example synonyms, grammatical variations, particularisations and generalisations, which must occur in a given relationship to other similar classes in a docu- ment in order for it to satisfy the search request as a potentially

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