A Tool for the Automatic Creation, Extension and Updating of Lexical Knowledge Bases

A TOOL FOR THE AUTOMATIC CREATION, EXTENSION AND UPDATING OF LEXICAL KNOWI.F.nGE BA.~F-g Walter M.P. Daelemans AI-LAB Vrije Universiteit Brussels Pleiniaan 2 Building K B-1050 Brussels Belgium E-mail: walterd@arti, vub.uucp ABSTRACT A tool is described which helps in the creation, extension and updating of lexical knowledge bases (LKBs). Two levels of representation are distinguished: a static storage level and a dynamic knowledge level. The latter is an object-oriented environment containing linguis- tic and lexicographic knowledge. At the knowledge level, constructors and filters can be defined. Constructors are objects which extend the LKB both horizontally (new information) and vertically (new entries) using the linguis- tic knowledge. Filters are objects which derive new LKBs from existing ones thereby optionally changing the storage structure. The latter use lexicographic knowledge. INTRODUCTION Despite efforts in the development of tools for the collection, sorting and editing of lexical information (see Kipfer, 1985 for an overview), the compilation of lexical knowledge bases (LKBs, lexical databases, machine read- able dictionaries) is still an expensive and time-intensive drudgery. In the worst case, a LKB has to be built up from scratch, and even if one is available, it often does not come up to the requirements of a particular applica- tion. In this paper we propose an architecture for a tool which helps both in the construction (extension and updat- ing) of LKBs and in creating new LKBs on the basis of existing ones. Our work falls in with recent insights about the organisation of LKBs. The main idea is to distinguish two representation levels: a static storage /eve/ and a dynamic knowledge level At the storage level, lexicai entries are represented simply as records (with fields for spelling, phonetic tran- scription, lexical representation, syntactic category, case frames, frequency counts, definitions etc.) stored in text files for easy portability. The knowledge level is an object-oriented environment, representing linguistic and lexicographic knowledge in a number of objects with attached information and procedures, organised in general- isation hierarchies. Records at the storage level are lexi- cal objects in a 'frozen' state. When accessed from the knowledge level, these records 'come to life' as structured objects at some position in one or more generalisation hierarchies (record fields ate interpreted as slot fillers). This way, a number of procedures becomes accessible (through inheritance) to these lexical objects. For the creation and updating of dictio~es, coll~- stmctors ate defined: objects at the knowledge level which compute new lexicai objects (corresponding to new records at the storage level) and new information ~n~hed to already existing lexical objects (corresponding to new fields of existing records). To achieve this, constructor objects mai¢ use of information already existing in the LKB and of the linguistic kaowledge r~re~nted at the knowledge level. Few constructors can be developed which arc complete, i.e. which can operate fully automati- cally without checking of the output by the user. Them- fore, a central part in our system is a cooperative user interface, whose task it is to reduce initiative from the user to …

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