MR 4 AP : Meaning Representation for Application Purposes (2023)

Abstract: Despite the significant progress made in Natural Language Processing (NLP) thanks to deep learning techniques, efforts are still needed to model explicit, factual, and accurate meaning representation formalisms. In this article, we present a comparative table of ten formalisms that have been proposed over the last thirty years, and we describe and put forth our own, Meaning Representation for Application Purposes (MR4AP), developed in an industrial context with a definitive applicative aim.

## introduction an efficient human-machine interface is one of the dreams of artificial intelligence (ai). in nlp, despite the dazzling progress of the last few years with the emergence of large language models, it is necessary to resort to formal representations of textual statements, so that the machine can structure its result and reason while providing the explanation. the last thirty years have witnessed numerous formalism proposals, the most recent of which are universal conceptual cognitive annotation (ucca, @xcite , abstract meaning representation (amr, @xcite , uniform meaning representation (umr, @xcite and babelnet meaning representation (bmr, @xcite . the adoption of a meaning representation formalism is not a trivial choice, especially in an industrial context, as is the case of the authors of this paper. in this context, it is required that a formalism be explicit and factual while maximizing the richness and accuracy of the most semantically salient linguistic phenomena @xcite . the contribution of this article is twofold. on the one hand, we facilitate the comparison of ten formalisms via a table (section 2). to the best of our knowledge, although it is one of the shortcomings expressed by the community @xcite , only @xcite and @xcite have established such a comparison 12 , but their studies and ours do not overlap much. moreover, we include the most recent formalisms. it is on this basis that we present our own, meaning representation for application purposes (mr4ap, section 3), which we are already exploiting in an industrial context with an applicative focus. in section 4, we put forward three examples of our representation choices, while section 5 describes the first version of an annotated corpus following our formalism as well as a first small-scale manual annotation effort, accompanied by the annotation guidelines. before concluding, we discuss some limitations and prospects for future work (section 6). ## meaning representations comparison in this section, we compare ten meaning representation formalisms, with which we compare our own (see partial coverage (#) has several meanings. it can mean that a feature is covered, but only in one of the formalism's extensions. this is the @xcite before covering english as well @xcite ) and groningen meaning bank (gmb, which was only for english @xcite before being extended to german, dutch, and italian with parallel meaning bank (pmb, @xcite ). the need to use an extension also holds true for amr, a formalism for which various works have aimed at making it multi-sentence (o' @xcite or enriching the annotated attributes (such as tense and aspect in @xcite . this is also the case for ucca with respect to coreference resolution (entities and events), which is dependent on a layer over the foundational one @xcite 3 . partial coverage can also mean that a feature is covered but only in a limited way. this is the case for relations that are numbered rather than named (:arg0, :arg1, etc., in amr), for labels that are insufficiently fine-grained (ucca), or when nodes carry the label that is traditionally assigned to the arcs (pdt-tl). this partial coverage mainly concerns the group of intra-and inter-sentence relations: when one of these relations is taken into account by the formalism, however this coverage is only realized at one of the two levels (for instance, umr's discourse relations), we consider that it is 3 other works have enriched ucca at different levels: role labeling of core @xcite and non-core @xcite arguments based on the supersenses of @xcite , refinement of implicit argument types @xcite , inter alia. ## mr4ap's position in this section, we focus on positioning mr4ap with respect to the other formalisms on the points that seem most salient to us. applicative aim. mr4ap is a formalism that has been designed with an industrial and, therefore, applicative aim. although we base our choices on existing research works, we have made them with the requirement of being factual, meaning that the annotation should not be left to the subjective interpretation of the annotator. there should not be several possible annotations for the annotator to choose from. therefore, despite the originality of their approach compared to other formalisms, we detach ourselves from uds's choices of continuous representation, mainly because such representation using probabilities can make the annotation process complex and be difficult to assess accurately. moreover, we move away from theoretical formalisms such as discourse representation theory (drt, @xcite and minimal recursion semantics (mrs, @xcite . genericity. mr4ap has been designed with genericity as its watchword. this applies both to the multilingual character of the representation and the invariance of the representations despite syntactic idiosyncrasies. most recent formalisms aim at abstracting away from syntax, and mr4ap joins them on this point. therefore, we detach ourselves from those that have a strong correlation with syntactic representations, as is the case of pdt-tl and uds. on the same note, and although they are only notation variants @xcite , the inverted arguments of amr and its extensions (:arg0-of) force parsers on the one hand to normalize relations (making graphs de facto multi-rooted), and on the other hand modify the graph, furthermore creating more cycles in supposedly acyclic graphs @xcite . mr4ap being multi-rooted does not allow inverted arguments. explicitness. from our point of view, a meaning representation must be as explicit as possible. this explicitness is expressed at several levels. on the one hand, we agree @xcite on the need to name all relations between nodes: if a relation is not typed with a sufficiently specified label (ucca), or is not usable without glossing (amr/umr), or is not represented by a discrete value (uds), much of the semantics attached to the relationship is lost. like bmr, mr4ap, therefore, uses a subset of verbnet roles, to which some labels are added to specify temporal, spatial, discourse, and coreference relations. likewise, it seems to us necessary to make entities' types as explicit as possible thanks to a label, mainly to avoid having to gloss their meanings. intra-and inter-sentence relations. we consider that a meaning representation would not be complete if it did not include the different rela-tions that exist in a document at the intra-and intersentence levels. in this respect, mr4ap is close to umr, because the latter includes a representation at the document level, although umr's is parallel to the one at the sentence level while mr4ap's isn't. umr's parallel document-level structure includes anaphora and coreference relations (between entities and between events), temporal relations between events, and modal relations, a representation unique to umr and based on the work of @xcite . thus, all discourse relations are excluded from their document-level representation, despite the carryover of the modal strength corresponding to the :condition and :purpose relations. mr4ap differs from umr on several points regarding inter-sentence representation. on the one hand, there is no distinction between the two levels, which are perfectly inseparable. on the other hand, and this follows from this single structure, in addition to coreference and temporal relations, all discourse relations are represented at both levels, simply because they can occur in adjacent sentences (see section 4). finally, modality is represented by an attribute linked to the predicate that is modified. attribute richness. following @xcite , we believe that a meaning representation of the text must include a certain amount of information conveyed by the morphosyntax. among this information, we can count grammatical tense, aspect, and number. it is precisely these three elements that are missing in amr and that motivated bmr's authors to incorporate them in their formalism @xcite , although in a minimal way. on the contrary, umr adds a lot of complexity by introducing deep lattices, multiplying the possible labels for each phenomenon. that holds true in particular for aspectual values with twenty-three possible labels against two for bmr (:ongoing + and :ongoing -) and seven for mr4ap, based on umr's work (habitual, state, process, atelic process, activity, endeavor and performance). this important multiplication of attributes and associated values is also visible for universal networking language (unl, @xcite and pdt-tl. we prefer a smaller set of attributes while keeping those necessary for an objective and factual representation of the textual content. ## mr4ap representation examples in this section, we apply our formalism to represent three distinct examples. each of these examples illustrates one or more parts of the formalism that we consider important. ## annotated corpora we first applied mr4ap to french short sentences from the tapaco corpus @xcite to ensure its usability on low-complexity sentences. we then applied it to more complex sentences from wikipedia articles in five languages to also test its multilingual compatibility. both datasets are available on the github repository foot_4 . ## limitations and perspectives although our formalism is able to address some shortcomings that other formalisms can't, some limitations remain. on the one hand, given all the elements that mr4ap represents, annotation remains a time-consuming and rather complex process. moreover, this complexity only increases with the length of the texts. the multilingual annotation experiment described above only exacerbated the need for a perhaps more efficient annotation strategy. on the other hand, while the annotation was carried out on texts in five different languages, the variety was somewhat limited: three of them are romance languages with few differences; english is a standard; only msa, due to its important differences with the other four languages, really allows us to conclude that mr4ap seems compatible with multilingualism. continuing the annotation effort with languages from different families or low-resource languages would enable us to support this assertion. moreover, from a cross-formalism perspective and following the recent mapping effort made between amr and umr @xcite , we would like to follow suit and align mr4ap to these two formalisms. this mapping would allow the production of a multi-formalism corpus, which could in turn allow the implementation of comparative experiments on the performance of each formalism from the same source material. important questions remain to be tackled: which tool to use/develop to annotate more efficiently with a formalism such as mr4ap? and how to ensure annotation completeness for a given text? does the level of anchoring have an impact on the explainability of semantic parsers (e.g., to source graph nodes)? knowing that graph linearization is an important topic and that edge ordering can have a "big negative effect" on the evaluation measures of some tasks @xcite , is rdf appropriate and what impact would this have on the performance of state-of-the-art parsers? ## conclusion we have highlighted the divergences and convergences between ten meaning representation formalisms. on this basis, we have put forth and 13 protégé: https://protege.stanford.edu/ positioned mr4ap, our application-oriented formalism. we have extensively described it both through guidelines and through several examples demonstrating its efficiency in representing meaning at the document level by taking into account discourse, coreference and temporal relations, its potential to represent some of the most complex linguistic phenomena, and its robustness to paraphrasing and multilingualism. we have also briefly presented the first version of the mr4ap-tapaco corpus as well as a first small-scale manual annotation effort to assert the multilingual compatibility of the formalism in practice. we concluded that mr4ap is usable regardless of the text's language, and this annotation effort allowed us to create the mr4ap-wikipedia corpus, which will serve as a gold standard. note that a hybrid semantic parser, which does not need any training data to annotate textual content, has been developed with this formalism, is already in production, and will be the subject of a future publication.