Sprucing up Supersenses: Untangling the Semantic Clusters of Accompaniment and Purpose (2020)

Abstract: We reevaluate an existing adpositional annotation scheme with respect to two thorny semantic domains: accompaniment and purpose. ‘Accompaniment’ broadly speaking includes two entities situated together or participating in the same event, while ‘purpose’ broadly speaking covers the desired outcome of an action, the intended use or evaluated use of an entity, and more. We argue the policy in the SNACS scheme for English should be recalibrated with respect to these clusters of interrelated meanings without adding complexity to the overall scheme. Our analysis highlights tradeoffs in lumping vs. splitting decisions as well as the flexibility afforded by the construal analysis.

## introduction creating a semantic annotation scheme is a delicate balancing act between two seemingly contradictory requirements. an annotation schemer must specialize their labels to segregate them in semantically meaningful ways, but whenever possible they must also generalize as to capture semantic similarities across varying labels. while this lumper-splitter problem pervades categorization efforts across disciplines, a linguistic annotation schemer faces an additional constraint: they must resolve the problem while making the schema accessible to annotators for the production of consistent annotations. generally, semantic resources have maintained the balance in one of two ways: by creating many fine-grained labels that are systematically organized into hierarchies or ontologies, or by resorting to very small number of distinct labels and making them conditional on the relation they annotate. framenet @xcite and the trips ontology @xcite exemplify the former approach, while propbank's numbered arguments @xcite illustrate the latter one. this paper focuses on the snacs framework of @xcite -a hierarchy of 50 semantic labels that seeks to characterize the semantic space of prepositions. like most resources, snacs falls somewhere in between the two extremes described above. what is unique about this scheme is that it tries to be as economical as possible with regards to the number of semantic types of prepositions it accepts into the hierarchy. however, it does so while being lexically agnostic of the identity of its syntactic governor (e.g., the governing verb). as a balancing mechanism between specialization and generalization of categories, it employs construals, a two-level annotation scheme: at the function level, it recognizes the semantics of individual prepositions, then at scene role level, it generalizes to the overall semantics projected by the frame or scene set by the verb or the construction. in this paper, we identify two areas within snacs that require attention, centered around the notions of purpose and accompaniment. the abstract concepts of purpose and accompaniment both span broad semantic areas, and contain many clusters of meaning, with nuanced differences between them. we argue that snacs treats both too simplistically, and by ignoring the nuances, makes annotation difficult. both accompaniment and purpose present an opportunity for lumping the various sub-categories of meaning into standalone labels, or splitting them into many finer ones. we ask whether the mechanism of construal offers a balance. our analysis suggests refinements to the existing snacs guidelines to handle accompaniment and purpose. with the case of accompaniment, we propose a more specialized set of labels to better capture the nunaces in the semantics. with purpose, we take the opposing approach where the definitions are further generalized in such a way that it is more amenable for edge cases. with an eye towards annotation, in both cases, we present tests that an annotator can employ to ascertain the boundaries of the new categories. ## background: snacs framework the semantic network of adposition and case supersenses (snacs) is a framework specifically created for the annotation of preposition semantics @xcite . snacs includes 50 broadcoverage semantic labels called supersenses, which is organized into three broad branches reflecting event participant roles (e.g., agent, theme, recipient), roles relating to the circumstance of an event (e.g., time, location, goal) and relational roles between two entities (e.g., identity, possession). a supersense label, thus, indicates the semantic relationship between the constituent object or the governing head of the preposition. unlike prior dictionary-based efforts in representing postpositional semantics @xcite , snacs labels the prepositions within its context (e.g., "cat on/locus the mat" vs. "found the cat in/locus the box") irrespective of the lexical type the target represents. snacs also utilizes the construal analysis, a mechanism that allows annotators to assign a preposition with two labels instead of one in a systematic manner. all prepositions are labeled at both the scene role and the function levels, where the scene role specifies the preposition's role with respect to the scene set by the governing head (typically a verb) and function label indicates the semantic contribution the preposition makes. construals are denoted by the convention scene role↝function. in examples (1a, 1b) above, the function label reflects the generalization that both of the examples indicate a location (as contributed by on). the scene role, however, recognizes the divergence in meanings triggered by the verb put. with (1c), the prepositional phrase represents the final goal much like (1b) but differs in its function label. ## accompaniment one of the most capricious english prepositions is the word with. it can take on many semantic guises, including instrument (open the door with a key) and manner (play the piano with gusto). here we are concerned with the meanings in ## purpose much like accompanier, purpose also demarcates a large semantic area and generally deals with motivation and intent of an action. in english, the preposition for is largely responsible for serving the role of purposive mediator in a given event. additionally, snacs annotation includes infinitive to that typically also marks purpose clauses alongside for. the snacs v2.3 guidelines define purpose as "something that somebody wants to bring about, [which is] asserted to be why something was done, is the case, or exists". purpose is often defined as expressing the 'why' of the event, indicating a desired outcome as the motive for an action. 6 (11) a. minerva rose to give a speech. q: why did she rise? a: to give a speech. b. he plays for trophies. q: why does he play? a: to (obtain) trophies. in practice, however, the semantic space associated with purpose, especially as expressed with infinitives element co-participant should be used to label phrases denoting people that are arrested. . . along with the suspect, or others that assist the authorities" @xcite . 5 it seems that the primary use of the role will always be overt: she was arrested with the deputy cannot have the reading of (9a) where an implicit party and the deputy are sharing in the arrest. 6 in the snacs hierarchy, purpose is a subtype of explanation, which additionally covers reasons that something happened which were not grounded in somebody's intention (e.g. we got wet due to the rain). and for-pps, is far from homogeneous. to and for in (12a, 12b) do not express why the event happened or should happen; rather they specify a general purpose or use for the governing head: a shoulder is needed for the use of crying and the particular place is great for the purpose of playing quidditch. in example (12c), the question of 'why' is out of place for the purpose clause, since for here supplies a product that can be obtained at the value specified by the governing head. ## additional related work in the literature, there is a broad spectrum of linguistic work about the concepts of purpose @xcite @xcite , inter alia) and accompaniment @xcite @xcite . the literature spans grammatical and syntactic issues, and defining the boundaries between purpose and accompaniment with respect to other semantic categories. however, space limitations prohibit an extensive discussion here. ## conclusion we have detailed a revised approach to categorizing semantic relations associated with various flavors of accompaniment and purpose as marked by english prepositions and infinitive clauses. our proposals involve restructuring the snacs inventory in some cases and better circumscribing current categories in others. we suggest revised definitions and paraphrase tests to better delineate groups of usages for annotators. english annotation applying the revised guidelines is planned, and we also hope to investigate how well these criteria can be adapted to other languages. our improvements have been implemented in the snacs v2.5 guidelines @xcite and the streusle v4.3 dataset release. 9