S imple NLG - TI : Adapting S imple NLG to T ibetan (2020)

Abstract: Surface realisation is the last but not the least phase of Natural Language Generation, which aims to produce high-quality natural language text based on meaning representations. In this article, we present our work on SimpleNLG-TI, a Tibetan surface realiser, which follows the design paradigm of SimpleNLG-EN. SimpleNLG-TI is built up by our investigation of the core features of Tibetan morphology and syntax. Through this work, we provide a robust and flexible surface realiser for Tibetan generation systems.

## introduction natural language generation(nlg) aims to produces natural language based on various input like meaning representations or numeric data. nlg systems can be classified into text-to-text or data-to-text system according to the system input. most early generation work in tibetan focused on text-to-text generation by neural networks, for instance, poem generation @xcite , machine translation @xcite , question answering @xcite . there is still a lack of theoretical studies and available resources for tibetan generation research. to solve the latter problem, this paper offers a practical tool, simplenlg-ti, for generating tibetan text. classical pipeline model @xcite proposed that a generation process shall accomplish six tasks, according to which the last but not the least phase of the process is surface realisation. surface realisation aims to produce strings that conform to grammar rules, therefore it plays an important role on improving readability of output. to build up simplenlg-ti, we solve key theoretical and practical problems in tibetan realising. firstly, we build up a linguistic rule bank for simplenlg-ti by exploring morphology and syntax features in tibetan such as function words, inflection, word order. secondly, in order to develop a practical surface realiser we investigate how to apply the framework of simplenlg-en to simplenlg-ti properly and reuse its code foot_0 . the rest of this paper is organised as follows. in section 2, we discuss some related work. in section 3, we discuss tibetan morphosyntactic characteristics and how to apply them into simplenlg-ti. evaluation process is introduced in section 4. and we end with conclusion and future work. ## related work as an important member of sino-tibetan language, tibetan has 3 major dialect areas in china and is used by about 8 million people around the world. a classic work(de körös, 1834) analyzed phonetic and morphology, and syntax features of tibetan. a primary feature of tibetan is its sov word-order, for instance, in the predicate of example (1) ཟ (eat) locates at the end of the sentence. moreover, there are abundant reductions in tibetan. both the original case ཡིས and its reduction form ས are correct in example (1). in most situation, the reduction form is preferred. as a significant phase of nlg, surface realisation has attracted much research attention and many surface realisers have been developed such as kpm @xcite , and openccg @xcite . simplenlg-en is an open source project @xcite , which allows it to be integrated into various language generation applications. for instance, in sentence generating @xcite and sentence summarizing @xcite . to realise well-formed text, simplenlg-en adopts rule-based approach based on lexicon and rules with rich linguistic knowledge. the paradigm of sim-plenlg has been successfully implemented into many natural language such as chinese simplenlg-zh @xcite and german simplenlg-de @xcite , and simplenlg-enfr @xcite . ## coverage of simplenlg-ti simplenlg-ti employs the framework of simplenlg-en because of its comprehensive linguistic component definition. in process of designing and developing simplenlg-ti, we firstly build up a component set contains content words, function words, and highlyfrequent phrases. then, to realise linguistic components into a well-formed string, we also establish a rule bank includes orthography, morphology and syntax rules by making use of linguistic knowledge in tibetan grammar books. the rich morphological features of tibetan lead to challenge for surface realisation task. in this work, we only focus on core morphological and syntactic characteristics that input code @xmath0.createclause() sentence.setsubject("ཤིང་མཁན་") sentence.addcase("གྱི ས་") sentence.addcomplement("ལྟ་རེས་ཡིས་") sentence.setverb("བཅད་") @xmath1.realisesentence(sentence) ## evaluation following the evaluation approach in early work @xcite , simplenlg-ti is evaluated by comparing its output with a golden standard. when an output is completely identical with the golden standard, then we take simplenlg-ti passes this unit test. in this work, we take a test set as our golden standard, which is manually translated from the test set of simplenlg-en. simplenlg-ti has successfully passed all 84 unit tests, which cover tibetan linguistic features previous described in this paper. the result shows that this work can be used as a practical tool for nlg in tibetan. ## conclusion in this work, we propose simplenlg-ti (a surface realiser) for tibetan generation, which is based on the framework of simplenlg-en. we investigate main linguistic features (morphology and syntactic characteristics) and apply them into the development of simplenlg-ti. the realisation results of simplenlg-ti show that it is capable of generating well-formed text and is feasible to be deployed in tibetan generation systems. in the future, we plan to improve the performance of simplenlg-ti by taking more features into account, for instance, other types of phrases like adjective phrases and complex words and phrases. moveover, we would like to test simplenlg-ti with practical tibetan generation systems. the full python package of simplenlg-ti will be publicly released on github foot_1 .