The robotic-surgery propositional bank

Robot-assisted minimally invasive surgery is the gold standard for the surgical treatment of many pathological conditions since it guarantees to the patient shorter hospital stay and quicker recovery. Several manuals and academic papers describe how to perform these interventions and thus contain important domain-specific knowledge. This information, if automatically extracted and processed, can be used to extract or summarize surgical practices or develop decision making systems that can help the surgeon or nurses to optimize the patient’s management before, during, and after the surgery by providing theoretical-based suggestions. However, general English natural language understanding algorithms have lower efficacy and coverage issues when applied to domain others than those they are typically trained on, and a domain specific textual annotated corpus is missing. To overcome this problem, we annotated the first robotic-surgery procedural corpus, with PropBank-style semantic labels. Starting from the original PropBank framebank, we enriched it by adding new lemmas, frames and semantic arguments required to cover missing information in general English but needed in procedural surgical language, releasing the Robotic-Surgery Procedural Framebank (RSPF). We then collected from robotic-surgery textbooks as-is sentences for a total of 32,448 tokens, and we annotated them with RSPF labels. We so obtained and publicly released the first annotated corpus of the robotic-surgical domain that can be used to foster further research on language understanding and procedural entities and relations extraction from clinical and surgical scientific literature.


Introduction
Surgery is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pathological condition such as a disease or injury, to improve bodily function or appearance, or to repair unwanted ruptured areas.The act of performing surgery is referred to as surgical procedure.In particular, robotassisted minimally invasive surgery is the gold standard for the surgical treatment of many pathological conditions since it guarantees to the patient shorter hospital stay and quicker recovery (Taylor et al., 2016).The robotic-surgical scientific literature is constantly evolving, and every year several up-to-date, high-quality academic papers and textbooks are published.They are an essential study material for medical students and professionals.Each (robotic) surgical procedure well documented in the literature, contains information on which are the main actions, which instruments must be used, which anatomical parts are involved, which are the precautions that must be taken for an adequate treatment of the patient and to what surgical step they are related to.The anatomical patients differences and the changes to the general procedure to manage them, are also often described.A surgical procedure then contains temporal, spatial and causal information between surgical actions.In addition to intra-operative treatment, pre-operative precautions and post-operative care are also often described.
These texts are meant and written for the understanding of human readers and therefore present the information in unstructured natural language.Having algorithms capable of both understanding the surgical natural language and organizing the content in a more structured and processable form, would pave the way for developing intelligent surgical and clinical systems: extracting knowledge from text, it would be possible to develop decision-making or question-answering systems that inform autonomous surgical robots, or help the surgeon, assistant or trainee to remember the operating steps, their order, the instruments to be prepared before the procedure, the anatomical parts to operate and precautions to follow before, during and after the surgery.These intelligent systems could help the surgeon to optimize the treatment of the patients on the basis of their anatomical features and their pathologies by providing theoretical-based suggestions (Wang et al., 2013).Furthermore, specific surgical language understanding and semantic role labeling systems can also be used to improve the automatic generation of operative images' captions (Zhang et al., 2021), a promising and active research-line also outside the biomedical domain (Bhattacharyya et al., 2022).
As much of this information comes in an unstructured form, Natural Language Processing (NLP) is crucial for transforming relevant information hidden in free-text into structured knowledge.As a large and complex domain, surgery uses a very specialized language, and the same concept may be expressed using semantically similar but syntactically and linguistically different expressions depending on the type of document or the writer's background.Creating NLP models capable of understanding the complexity of surgical language is extremely useful in improving healthcare and advancing medicine, but having high quality and specialized available data is an essential requirement to advance in this line of research (Locke et al., 2021).
Although efforts have been made to adapt NLP models to medical language (Chen et al., 2018;Houssein et al., 2021;Locke et al., 2021), few have addressed the surgical subdomain, probably due to the lack of annotated data and the high costs involved in producing them.To fill this gap, with this paper we publicly release the first annotated dataset for the Semantic Role Labeling (SRL) task (Palmer et al., 2005) applied to the robotic-surgical domain.It consists of sentences describing surgical procedures manually annotated with PropBank-style frames (c.f., actions) and their semantic roles (c.f., the agent performing the action, the anatomical part being operated during the action, etc.).Sentences are taken as-is from multiple sources, i.e., different books and academic papers, and written by various authors, so to capture possible variations of language.
This paper substantially extends and completes our previous work (Bombieri et al., 2022), where we presented a framebank for the robotic-surgical domain, i.e., a PropBank-style repository collecting frames describing actions and participants used in the robotic-assisted surgical domain.That is, while in Bombieri et al. (2022) we presented the catalogue of semantic labels to be used, in this paper we contribute a fully annotated dataset exploiting these labels.More in details, the extension and the novel contributions of this work with respect to (Bombieri et al., 2022) include: • the full, manual annotation of a textual dataset consisting of 1,559 sentences with the semantic labels of the framebank presented in (Bombieri et al., 2022); • the description of the annotation process, including the annotators' training and the annotation guidelines; • the public release of the annotated dataset.
We believe that this first manually annotated dataset for surgical natural language understanding is usable for extracting ad-hoc semantic surgical and clinical information from real academic textbooks and papers and that it can pave the way for applying NLP in the surgical domain, with great benefit for human operators and clinical research.
The paper is organized as follow: Sect. 2 deals with related works.Section 3.1 presents the Robotic-Surgery Procedural Framebank (RSPF).Section 3.2 describes the method adopted to annotate sentences using RSPF labels.Section 4 reports statistics and details about the annotated dataset.Finally, Sect. 5 summarises obtained resource and describes future works directions.

Background
Researchers traditionally have built NLP lexical resources targeting general-domain English, which is syntactically and semantically different from domain-specific usage (Wang et al., 2013) as well as other languages (Moeller et al., 2020).Therefore, these resources cannot be directly exploited in very specific domains or with other languages, and different methods have been proposed to adapt them to specific needs.Updating the semantic frames bank can be viewed as a data-driven way for adapting algorithms for general purpose domains to more restricted and specialized texts.This section summarises some works that have adapted the general linguistic resources to the specific domain or to languages other than English.
Many works on updating English frame banks have been carried out in various fields, such as the clinical (Albright et al., 2013;Wang et al., 2013), the biomedical (Chou et al., 2006;Majewska et al., 2021), and other non-biomedical domains such as software analysis and cooking recipes (Jiang et al., 2020;Wang, 2015).Wang et al. (2013) has considered texts written in different laparoscopic cholecystectomy operational notes stating that the language is significantly different from general English and existing semantic resources have limited coverage of the action verbs that frequently occur in operative notes.Based on these observations, the authors have surveyed the usage of each verb in the sample dataset to determine the verb meanings and semantic arguments of each one.In this way, they have extracted a set of differently used verbs, and, following the PropBank guidelines, they have defined specific frames for them.This work, however, has considered only surgical, non-robotic procedures taken only from gastrointestinal surgery notes that use more schematic language than descriptions taken from textbooks used in our work.Finally, no annotated dataset with these newly defined frames was provided, hindering the possibility to benchmark available SRL tools on the considered domain.Albright et al. (2013) has annotated clinical narratives with layers of syntactic and semantic labels to facilitate advances in clinical NLU.Following PropBank guidelines, new frames have been defined in a similar manner to the method described in our work.
Although the dataset has dealt with a clinical language, our work considers a more specialised level, i.e., descriptions of robotic-surgical procedures, a restricted subset of the clinical domain considered by the paper (which includes for example disorders, physiology, chemicals and groups, anatomical notions, etc.).Unfortunately, the related dataset is no longer freely accessible due to copyright issues (Peng et al., 2020).Chou et al. (2006) has presented a corpus of PropBank-style annotations for biomedical journal abstracts.The work has analyzed 30 biomedical verbs adding or modifying their meaning with respect to general English resources.Then, a semi-automatic method has been applied to annotate a collection of MEDLINE abstracts selected from the search results with the following keywords: human, blood cells, and transcription factors.First, predicate candidates were identified; then, an automatic tool was used to produce biomedical semantic roles; and, finally, the resulting annotations were manually corrected.In Majewska et al. (2021), a new resource that provides VerbNet-style (Schuler, 2006) frames for biomedical verbs is released, together with the presentation of key differences between the general and biomedical domain, and the design choices made to accurately capture the meaning and properties of verbs used in biomedical texts.The conclusion is that leveraging a specialized VerbNet helps systems to improve verb classification and thus to better tackle challenging NLP tasks in biomedicine.The two previous works have dealt with a biomedical language that is still very far from the procedural surgical one; moreover, the second one has dealt with VerbNet classes that are quite different from the PropBank frames adopted in our work.
Outside the medical domain, (Wang, 2015) has proposed a method for automatically extracting semantic information from software requirements specifications.First, frequent verbs were selected from software requirement specification documents in the e-commerce domain, to build the semantic frames for them.Then, selected sentences were annotated for using them as training material to benchmark different machine learning methods.Jiang et al. (2020) instead has proposed a new annotated dataset for extracting information from recipes.The authors have defined ad-hoc entity types (action, food, tool, duration, temperature, condition clause, purpose clause and others) and relation types following the methodology of PropBank.Then a corpus was annotated and used to benchmark a neural span-based model extracting entities and relationship.
Finally, (Bakker et al., 2022) has applied a transformer-based SRL approach to map legislation from semi-free text to structured manually defined frames composed by fixed semantic roles.Obviously, the domain is completely different from the one of our paper, but the approach bears some similarity.
There are also several works proposing PropBank language-specific lexicons for languages other than English, both for specialized or general domain.For example, (Antony et al., 2020) has performed a SRL task in Tamil Biomedicine texts, extracting domain specific verbs and related semantic roles.Kara et al. (2020), Mirzaei and Moloodi (2016), Moeller et al. (2020) instead have built a general-domain PropBank specific for Turkish, Persian and Russian respectively.Jindal et al. (2022) has stated that despite the availability of SRL resources in different languages, it is almost impractical to build a single multilingual SRL labeler because of the differences in semantic labels and framebanks.To provide a possible solution to these issues, it has provided a family of auto-generated PropBanks for 23 languages from 8 language families, together with a small set of manually annotated sentences for Polish (100), Portuguese (3779) and English (16622), with the goal of enabling the construction of SRL models for resource-poor languages by annotating the text in different languages with a layer of universal semantic role labeling annotation.

Building the robotic-surgery procedural propositional bank
The Robotic Surgery Propositional Bank (RSPB) is an extension of PropBank (Palmer et al., 2005) for the robotic-surgical domain.We recall that PropBank consists of: • a framebank, i.e., a collection of frames (a.k.a., meaning or senses) for lemmas denoting predicates (verbs or nominalized verbs).Frames are specific to a given lemma, and each lemma has one (monosemous lemma) or more (polysemous lemma) associated frames.Moreover, each frame provides the specification of its semantic roles, i.e., the different labels that can be used to semantically characterize the arguments of the corresponding predicate.• a corpus of text annotated (according to the framebank) with information about basic semantic propositions.
Following the steps described in (Palmer et al., 2005), also the development of RSPB is divided into two parts, namely the creation of a lexicon of frames files (RSPF, i.e., Robotic Surgery Procedural Framebank) summarised in Sect.3.1), and the annotated dataset with RSPF's labels, presented in 3.2.Figure 1 shows a general overview of both steps: in the domain-verbs framing process, some automatic methods extract lemmas describing actions from roboticassisted surgical texts.How often they appear in the target domain (freq_i) is compared to how often they appear in OntoNotes Weischedel et al. (2017) (freq_i').To take into account the different sizes of the datasets, the comparison is conducted on relative frequencies (i.e., obtained normalizing the number of occurrences of a given verb over the total number of verb tokens in the corresponding dataset).If freq_i freq_i', i.e., the ratio between the two is greater than a fixed threshold, then the respective lemma is sent to a team of human linguistic experts that verify to which of the categories described in Sect.3.1.1 the lemma belongs, modifying the corresponding frameset if necessary.The final frameset is validated by a clinician and publicly released.During the annotation step, a team of annotators is hired and trained.Annotation guidelines are written and sentences to annotate are provided.Then, the annotation process is performed.Quality checks are periodically carried out and, if necessary, the training step is resumed.

The robotic surgery procedural framebank
For identifying procedural verbs and nouns used in the robotic-surgical domain, two strategies are applied.The first one (Sect.3.1.3)deals with the detection of actions expressed by nominalized verbs, and it is based on keyword extraction.The second method (Sect.3.1.4)is based on Part-Of-Speech (POS) tagging, and it is used to detect actions expressed by verbs.Their combination, together with additional low-frequency or missing candidates suggested by the clinician during the validation phase, offers a broad coverage of the robotic-surgery actions for considered domains.

Adapting PropBank to the robotic-surgical domain
RSPF is an adaptation of the latest release (version 3.1) of PropBank Palmer et al. (2005) to the robotic-surgical domain, i.e., the field of medicine that involves the use of robotic systems to perform surgical procedures.These systems use robotic arms and specialized tools to perform minimally invasive surgeries with greater precision and control than traditional human-performed surgical methods.This domain is substantially different than the general English one considered in PropBank, and thus this adaptation is necessary for extracting meaningful robotic-surgical procedural knowledge.By analyzing the semantic use of each lemma describing an action identified in the corpus (see Sect. 3.1.2for details on the considered corpus) with respect to the PropBank framebank, each candidate is assigned to one of the four categories described in Table 1.
If a lemma is assigned to the PRESENT class, no changes are needed, since PropBank already covers the robotic-surgical usage (i.e., there is a frame for the lemma that perfectly describes that usage of the predicate).
If a lemma is assigned to the MISSING_ROLE class, some semantic roles important for the robotic-surgery domain are missing, and therefore they must be added.The lemma "to retract" is an example of action belonging to this category.For it, PropBank offers the "retract.01:to take back" frame which actually covers the typical meaning of the surgical domain.However, only two roles are proposed for it: • Arg0: taker back, agent • Arg1: thing retracted The lemma is already present in PropBank and there is a frame file that adequately describes the use of the predicate.For this lemma, PropBank already describes appropriate semantic roles as core entities

MISSING_ROLE
The lemma is already present in PropBank, and there is a frame file that adequately describes the use of the predicate.This frame, however, does not include domain-specific semantic roles often used in our domain

MISSING_FRAME
The lemma is already present in PropBank, but a proper frame is missing, as the existing ones describe different meanings

MISSING_LEMMA
The lemma is not present in PropBank The verb to retract is however used very often in the robotic-surgery domain, together with additional information that allow to better describe the action: the instrument used for the retraction, the technique and/or manner, and the ending point or the indication of how much to retract.Example (1) shows a domain sentence where some of these additional roles of verb to retract are present. (1) The mediastinal pleura is then retracted posteriorly with cadiere forceps (arm 3).
A candidate lemma may be assigned to the MISSING_FRAME class for two different reasons: i) the usage of the lemma is semantically and entirely different from all the frames covered in PropBank, and there is no overlap between the existing and new semantic roles; ii) the meaning is not completely new, but the existing frames are too broad to be useful for the robotic-surgery domain, i.e., the new frame deals with a subset of the meaning captured by (some of) the old ones.An example of the first case is the verb "to grasp".For it, PropBank offers a single meaning "grasp.01: to take hold of, comprehend" with two semantic roles: The robotic-surgical domain uses this lemma with a significantly different meaning, i.e., "to clasp or embrace especially with the fingers or arms".For it, important information is also the grasper, the thing grasped, the instrument used for grasping, and important spatial indications for correct grasping.Example (2) shows a domain sentence with this different use of "to grasp", where some of its specific roles are present. (2) Using the cadiere grasper (robot arm #3), grasp the soft tissues along the lesser curvature of the stomach to straighten out the lga perpendicular to the celiac axis.
An example of the second case is the verb "to approximate".For it, PropBank has the frame "approximate.01:to be close or similar, cause to come near to or approach again" with only two roles: • Arg0: entity coming close • Arg1: entity coming close to It offers a broader meaning than the specialized one used in the robotic-surgery domain ("to come near in position, to bring near"), which is typically enriched with the following information: agent, entity coming close, entity coming close to, instrument and spatial indications.Example (3) shows a domain sentence with this different meaning of "to approximate", where some of its specific roles are present. (3) Next, the musculofascial plate of the rectourethralis is approximated to the posterior neobladder, approximately 2-cm posterior to the planned urethral aperture, using 3-0 polyglactin suture.
Finally, an example of a lemma of class MISSING_LEMMA is the noun "traction".
In surgery it refers to "pulling force to treat muscle and skeleton disorders".For it, important information is the tissue being tractioned, the instrument used to perform the action, and relevant spatial indications.Example (4) shows a domain sentence involving "traction" together with some of its specific roles.
(4) Upward traction of the prostate using fourth robotic arm or assistant

Collecting domain-specific lemmas
To extend PropBank to the procedural robotic-surgical domain, those verbs (or nominalized verbs) that are typical of the surgical domain have to be identified.The Surgical Procedural Knowledge Sentences (SPKS) dataset, presented in (Bombieri et al., 2021) is used to extract the domain actions of the procedural robotic-surgical domain.To the best of our knowledge, it is the only publicly available corpus of this domain.1It describes 20 different robotic-surgical procedures belonging to four different disciplines: urology, gastrointestinal procedures, thoracic procedures and gynecology.
For the comparison with general English we have instead considered the OntoNotes dataset.It is a large annotated dataset comprising various genres of text such as news, conversational telephone speech, weblogs, usenet newsgroups, broadcast and talk shows.
The two methods presented in 3.1.3and 3.1.4are used to extract domain-specific actions from SPKS.For each domain-specific predicate, it is then necessary to check to which of the categories described in Table 1 the lemma belongs and proceed with framing as described in 3.1.5.Table 2 shows 10 examples of actions expressed by nouns identified by the method described in 3.1.3,and 10 examples of verbs identified by the method described in 3.1.4.For each of them, the indication of the type of modification that has been requested on PropBank is reported.Finally, as frequencybased methods for extracting domain terminology may miss some very specific terms rarely used in text (thus ensuring high precision but low recall), the final list of extracted candidate verbs and nominalized verbs was double-checked also by the clinician in the validation phase, for suggestion of possible missing domain-relevant verbs (and some examples of usage), thus improving the overall coverage of the domain.These additional verbs were then formalized in RSPF following the same framing process described in Sect.3.1.5.

Finding frame-evoking nouns
In medical English, actions can be frequently expressed using nouns rather than verbs.For example, the noun "suturation" can be used to express an executable action.Below are two semantically equivalent sentences, where in the first the concept is expressed using a verb, and in the second using a nominalized verb: (5) At this point, the surgeon sutures the vein.
(6) At this point a suturation of the vein is carried out.
For nouns, the task of domain action detection is addressed as a keyword extraction problem, i.e., the identification of the lexical entities that best represent the domain according to a reference corpus.It is traditionally used in numerous fields to improve methods for browsing, indexing, topic detection, classification, contextual advertising and automatic summarizing of texts both with supervised and unsupervised approaches Hasan and Ng (2014).For our purposes, we have adopted the method proposed in Campos et al. (2020).It is an unsupervised approach (and thus it does not require annotated training data), built upon local text statistical features extracted from documents.It is corpus-, domain-, and language-independent, so it can be also adapted to the robotic-surgery field.
From the output of the algorithm, only nominalized verbs are selected.Since the most common morphological process involved in nominalization is derivation that can be defined as the creation of a new lexeme by the addition of an affix (i.e., a bound grammatical morphemes) (Varvara, 2017), obtained results are filtered keeping only those words ending with one of the following suffixes: "-sion", "-son", "-tion", "ness", "-ment", "-ery", "-ence", "-ance", "-ure", "-ize", "-ify".False positives are finally removed from the list by manual revision.

Finding frame-evoking verbs
For verbs, a simple approach that compares the frequency of terms with an action role between the SPKS and OntoNotes corpora is used.For each token of the domain text, its POS tag (Bird, 2006) and the number of its occurrences are calculated.Finally, sentences of the corpus in which it is used are retrieved.Only the tokens whose POS tag denotes a verb (i.e., VB, VBP, VBZ, VBD, VBN or VBG) are retained.2Lemmatization is then applied, and each token (e.g., "cauterized", "cauterizes", "cauterizing") is associated to the corresponding lemma (resp., "cauterize"), aggregating number of occurrences appropriately.For each obtained lemma, the relative frequency with which it appears in domain sentences is then calculated and compared with the one the same lemma appears in OntoNotes.Finally, only those lemmas that are very frequent in the domain sentences and only rarely used in OntoNotes (i.e., in which the ratio between the two relative frequencies is greater than a given threshold empirically set) are considered as "in domain".More in detail, for each verb in SPKS, the ratio between the two relative frequencies is computed, and then the verbs are sorted in descending order, from the one with the greatest ratio to the smallest one.The resulting ordered list is manually revised and the cut-off threshold is set so that, of the verbs having a ratio greater than it, at most three of them are judge as not domain-specific by domain experts.For instance, this method identifies as "in domain" verbs like "cauterize", "detubolarize" and "extraperitonealize", because they are frequent in surgery and very rarely used in general English and therefore the ratio between the frequencies of these verbs in the two different domains is very high.On the other hand, the method recognizes verbs such as "need", "aid" and "see" as "general English" because they appear in the two corpora with similar frequencies.

Framing of domain-actions
The processes described in Sects.3.1.3and 3.1.4allow to obtain a list of domain verbs and nominalized verbs associated to a list of SPKS sentences where they are used.Each lemma and the respective sentences are then analysed by domain experts to understand to which of the categories described in Sect.3.1.1 the lemma belongs to.
The framing was performed by three linguistic experts with a 3-year experience in the robotic-surgical domain and validated by a clinician.All frames are collected in XML files.Figure 2 is an example of the corresponding XML file for the lemma approximate.In the case MISSING_LEMMA, the lemma is not present in PropBank, and thus it is an unknown word for the resource.Domain experts therefore perform the following actions: (i) they add the new lemma to the resource; (ii) they add a new frame to the inserted lemma; (iii) they provide a textual definition of the meaning of that lemma in the surgical domain taken from online medical dictionaries, in particular Webster Dictionary3 and The Free Medical Dictionary4 ; (iv) they add appropriate semantic core roles; (v) they add at least one example of SRL-style annotation for the new frame.
In the case MISSING_FRAME, the lemma is already in the resource, but with inappropriate frames.In this case, domain experts perform only steps (ii)-(v).
In the case MISSING_ROLE, the lemma is already in the resource with an appropriate frame, but with an inappropriate set of core roles.In this case, steps (iv-v) are performed.
Finally, in the case PRESENT, the lemma is already in the resource, with an appropriate frame and core roles.None of the previous steps are performed.
During step (iv), a role is considered as core, if arguments playing that role occur with high frequency in the corpus' sentences that use that lemma (i.e., it is present in more than 50% of sentences where the lemma is used)5 or, independently of its usage in the corpus, if it is considered fundamental by domain experts for the interpretation and representation of the action.

Framing effort
The framing step is quite expensive because it is carried out manually by personnel who must have expertise both in linguistics (SRL annotations in PropBank style) and in the robotic-surgical domain.The framing step took about 80 h to be completed.

The robotic surgery procedural propositional bank
This section presents the annotation process of sentences from the robotic-surgical domain according to the frames and roles defined in RSPF.In particular, Sect.3.2.1 introduces the annotation team.Section 3.2.2discusses the texts to be annotated and their typology.Section 3.2.3describes the annotators training process.Section 3.2.4details the tool used to annotate the sentences and the adopted post-editing technique.Section 3.2.5 describes the annotation process and provides annotation guidelines.Finally, Sects.3.2.6 and 3.2.7 discuss inter-annotation agreement and training effort respectively.Through these steps, RSPB has been created.RSPB wants to stimulate research in the field of natural language processing applied to robotic-surgical texts.In particular, it is designed for the SRL task, which is the basis of many NLP applications.SRL is traditionally framed as either a dependency-based (Surdeanu et al., 2008) or a span-based (Carreras & Màrquez, 2005) labeling task.Given a predicate in a sentence, the difference between the two settings is in the formalism used to represent its arguments.Span-based SRL requires the identification and classification of the entire textual span of an argument, whereas dependency-based SRL is concerned about labeling only the head of the argument.In the dataset developed in this work, sentences are annotated in a span-based fashion.

The team
A team of four people with different roles has carried out the annotation process.In more detail, the team is composed by: • Two annotators.They are bachelor's students of linguistics.During their studies they have already encountered issues related to semantic annotation of corpora and successfully passed the relevant exams.However, they never delved into PropBank style annotation.They have an excellent knowledge of the English language (C1 language level) but they have no knowledge of the medical domain.They were involved in the project with a student collaboration contract of 150 h each.They were exclusively concerned with the annotation work.The total of the sentences were annotated by the two annotators with the following proportions respecting the needs and timing of each: the first one annotated approximately 65% of the sentences while the second the remaining 35%.During the annotation, the project leader revised approximately 1/5 of their annotations to find recurring errors and improve the guidelines accordingly.The annotators processed and labeled a different number of sentences at the same time: this shows that the task, due to the high concentration and the fatigue load lends itself to being carried out in a different way according to human characteristics and skills.Due to cost reduction strategy and financial possibilities, the surgeon was just involved in the role of answering doubts, instead of having him participating directly into the annotation process.

Text to annotate
The team annotated sentences of different surgical procedures, taken from different documents and written by different authors.They vary greatly in the writing style: the procedure descriptions are essential and schematic in some cases, while longer sentences enriched with background information are used in others.In more detail, we asked to annotate an extended version of the procedural part of SPKS dataset.In total, we relied on 1,559 annotated sentences describing 28 surgical procedures of four different robotic-surgery sub-domains, whose distribution is summarised in Fig. 3.All the sentences are therefore procedural, in the sense described in (Bombieri et al., 2021).Approximately 80% of the sentences are taken from robotic-surgery textbooks describing how-tos of surgical procedures, while 20% from academic papers or case reports dealing with academic research on surgical procedures or descriptions of real interventions on specific patients.

Training process
The annotators, despite having basic knowledge of linguistics and semantic roles annotation, did not know the PropBank style of annotating spans of text.In a first step, during two workshops of one hour each, the project leader introduced the annotators to the project, the ultimate purpose of these annotations, PropBank and PropBank style SRL annotation, and the annotation tool.
At the end of these workshops the annotators were asked to annotate 15 general English sentences of increasing complexity following the PropBank annotation guidelines.At the end, the annotation was evaluated by the project leader.The process was repeated with new sentences until a 90% inter-annotator agreement (IAA) with the project leader was reached, following a similar approach to the one presented in (Hovy et al., 2006).
Then, the project leader introduced RSPF to the annotators, focusing on the differences compared to PropBank.The same annotation experiments was conducted, but this time on surgical domain sentences instead of general English ones.Although the annotation guidelines are similar, this experiment was intended to measure the understanding of the surgical text by the annotators.The project leader analyzed and discussed the errors of the annotators and refined the guidelines providing them with more explanations to fill the doubts, until a 85% inter-annotator agreement with the project leader was reached. 6Both arguments labeling and the choice of predicate's meaning were evaluated. 7hen, during the actual annotation of the whole dataset, the project leader analyzed 20% of the sentences of the two annotators and organized weekly meetings with them discussing possible mistakes and answering their doubts.The annotators were then asked to revise the labeling if needed be, and to double-check the previous annotations in light of the new indications.
At the end of the dataset annotation process, 60 SPKS sentences were assigned to both annotators, which were asked to annotate them in parallel without confronting each other.The inter-annotator agreement on these annotations was calculated as reported in Sect.3.2.6,both on predicates and arguments labels.

The annotation tool and post-editing technique
To reduce the annotation effort, a semi-automatic annotation approach was adopted.In a first step, the dataset was processed with a general English span-based SRL tool (Shi & Lin, 2019) for automatically obtaining PropBank annotations of the sentences in CoNLL-2012 format.
The annotations thus automatically obtained were uploaded on a server running Inception (Klie et al., 2018), a tool supporting SRL-style labeling of text.Inception has been setup to allow user friendly SRL annotation of the sentences.The annotators were asked to post-edit and revise the PropBank annotations according to RSPF and the given guidelines (see Sect. 3.2.5).That is, instead of having to manually annotate the sentences from scratch, the annotators were asked to revise (i.e., adding missing annotations, deleting wrong annotations, changing wrong PropBank frames and roles to appropriate RSPF ones) the automatically provided candidate annotations, so to substantially reduce the annotation workload.
Figure 4 shows an excerpt of the graphical user interface of the tool with an example of annotation, and the corresponding content in CoNLL-2012 format, which is directly readable by state-of-the-art SRL methods.

Annotation process and guidelines
The RSPB dataset follows the PropBank style of annotating predicates and semantic arguments (Palmer et al., 2005).Accordingly, similarly to PropBank, our corpus is a collection of sentences with verbs and nominalized verbs annotated with the corresponding sense id (also known as a "frameset" or "roleset" id in PropBank) in RSPF, together with their related semantic arguments.
These semantic arguments are labeled according to some predefined categories (e.g., Arg0, Arg1, Arg2) whose specific meaning typically varies according to the predicate considered.The set of roles of each predicate is outlined in the corresponding RSPF frame that gives both semantic and syntactic information about each sense together with correspondences between the number and semantics.Numbered arguments (e.g., Arg0, Arg1, Arg2) reflect either the arguments that are required for the valency of a predicate (e.g., agent, patient, benefactive), or those that occur with high-frequency in actual usage (e.g., instrument, surgical technique, important spatial constraints) as explained in Sect.3.1.In addition to numbered roles, RSPF adopts also the same modifiers of PropBank (e.g., ArgM-TMP, ArgM-PRP).Differently from the numbered ones, modifier roles are general and not frame specific.Examples are ArgM-TMP, denoting temporal information, ArgM-PRP, related to the purpose of the corresponding predicate, and ArgM-ADV indicating general adverbial information.The annotation of sentences with this information creates a dataset, which can be used as training data for a variety of medical natural language processing applications.However, for the annotations to be reliable it is necessary to follow a rigorous annotation process and precise guidelines.Since our corpus is a specialization of PropBank to the surgical domain, it therefore inherits a good part of the annotation guidelines from it.
The main tasks of the Robotic-Surgery Propositional Bank annotation are: (i) to identify the predicates of the sentence if not already labeled by the automatic tool.(ii) to choose a sense in RSPF for each predicate or verify if the one automatically assigned is correct; (iii) to label core arguments for each predicate or verify if the labels automatically assigned are correct.(iv) to label modifiers arguments if present or verify if the labels automatically assigned to them are correct.
For each sentence, step (i) is related to the predicate-level annotation.The annotators have to check the correctness of the automatically identified predicates, as well as to identify missing annotations (i.e., predicates not tagged as such by the automatic tool).
If the algorithm has marked as a predicate a token that does not cover this role, it must be removed together with all the annotations of the arguments related to it.This case is quite rare since state-of-the-art algorithms tend to have a rather high ability to identify predicates.Examples that can sometimes mislead algorithms are those that contain highly-specialized domain expressions such as running suture which in surgery indicates a particular technique for closing the deep portion of surgical defects under moderate tension, while an algorithm not trained in medical language could interpret it as to run verb.Furthermore, the tool we used for automatically generating the candidate annotations also annotated modals and copulas.The annotators were asked to remove them (as verb) since for the purpose of procedural knowledge extraction, i.e., the extraction of surgical actions and semantic arguments linked to them, we deemed them not useful.Annotations of the modals have been kept however at the modifier argument level (with arguments ArgM-MOD) because they can be helpful to specify the obligatory nature of the corresponding action.Finally, in this step also some nominalized verbs, i.e., those nouns that refers to actions, have been annotated as predicate.At this point the step (i) is finished and annotators continued with the step (ii).
Step (ii) is still related to the predicate-level.At this point the annotators have a list of predicates to disambiguate using the corresponding RSPF file.For most of the general English predicates, the automatic tool will have already proposed an appropriate sense which must only be verified by the annotators.If for it RSPF distinguishes two or more verb senses, annotators are asked to choose the one that best suits the context.In some cases the process is straightforward because RSPF has only one available sense.This is the case of monosemous predicates, either specific of the surgical domain (e.g., skeletonize, detubularize or kocherize) or general English ones (e.g., accomplish or avoid).In other cases, the disambiguation is more complex because there are multiple senses in RSPF.Cases of this type can be further divided into two sub-categories: • one of the lemma's senses is specifically used just in the surgical domain, while the other general English senses are rarely used in surgical procedural texts.An example is the lemma grasp, for which RSPF has two senses: grasp.01:"to take hold of, comprehend" clearly related to a general English usage; grasp.02:"to clasp or embrace especially with the fingers or arms" specific to the surgical use.
In this case the disambiguation is typically straightforward, as the general English sense is not or only rarely used; • the lemma has both general English and surgical-specific senses that may both occur in surgical procedural texts.An example is the lemma follow, for which RSPF has 9 senses.Although sense 09 "move behind in the same direction" has been added for surgical purposes, other general English senses are used as well in surgical texts, for example the 01 "be subsequent, temporally or spatially".The disambiguation in these cases is more complex and the annotators are asked to reflect well on the meaning of the sentence, comparing it with available examples in RSPF, and to discuss with the project leader if necessary.
During step (ii), occasionally, annotators may come across predicates that do not have yet an existing entry in RSPF. 8In these cases, annotators are instructed to contact the project leader describing the situation and reporting the corresponding dataset's sentence.The project leader analyzes the corresponding sentence and lemma and then he decides whether to add this lemma to RSPF (because it is a lemma with a surgical sense that was not covered in the initial construction of RSPF), or to ignore the case (when the lemma is only a rarely used surgical slang).The project leader may also consult the surgeon to take an informed decision.
Once the correct meaning of a predicate has been identified, annotators proceeded with step (iii), the argument-level annotation.While Arg0 is typically relative to the one who performs the action and Arg1 typically relative to the one who undergoes it, for the other numbered arguments RSPF has to be checked more carefully.The annotators has to analyze all the arguments (both core and modifier) automatically identified by the tool, as well as possibly arguments in the text not annotated by the automatic pre-processing, which are then added from scratch by the annotators.For core arguments, if the annotation label is not correct, the most appropriate numbering has to be inserted.For the arguments automatically labeled as modifier, the annotators have to check if a more appropriate core role is available in the roleset of the frame, and, if so, to replace the modifier with it.
Since the tool used for obtaining the first draft of the annotations is trained on general English text, i.e., it does not know the RSPF specific frames and roles added in the extension of PropBank, the case of spans annotated automatically with a modifier (for PropBank) instead of core role (for RPSF) is quite frequent.Consider the following examples: The proximal rectum is grasped using laparoscopic forceps. (8) The gastric pouch is created using a perigastric technique.
In example ( 7), a PropBank-based SRL tool will likely recognise "using a laparoscopic forceps" as a generic ArgM-MNR entity while in RSPF the instrument that should be used to grasp something is labeled as Arg2 of the sense 02 of the lemma grasp.In example ( 8), a PropBank-based SRL tool will likely recognize "using a perigrastric technique" as a generic ArgM-MNR entity, similarly to the previous example, while in RSPF the surgical technique is identified with the core role Arg5 of the sense 01 of the lemma create.9RSPF contains annotation examples also at this level to help annotators.In most cases, choosing a role is straightforward, given the verb specific definition of the label in the frame files.However, in some cases, it may be difficult to understand how to annotate a span of very specialized text.The annotators have to decide between the available labels based either on the explanations/examples provided in RSPF or by searching online the meaning of unknown domain words.If the doubt persists, the project leader is consulted.
During step (iv), for modifier arguments not to be translated into an RSPF core role according to step (iii), annotators are asked to verify whether the annotations proposed by the automatic tool is consistent with the guidelines of the original PropBank, and if not to correct them.RSPF does not add new modifier tags to PropBank, so no changes to its guidelines were necessary for these aspects.
Regarding which token to include in the span of the annotation (c.f., span boundaries) and corresponding exceptions, the same indications as in the PropBank's guidelines are given to the annotators.

Inter-annotator agreement
Agreement between the two annotators has been measured at the end of the process on a sample of 60 sentences annotated by both, using the kappa statistic (McHugh, 2012), which is defined with respect to the probability of inter-annotator agreement and the agreement expected by chance.The kappa statistic has been computed both for predicates and arguments, obtaining the values 0.89 and 0.88 respectively.These values denote an almost perfect level of agreement between the annotators, reassuring on the adequacy of the annotation process and guidelines.

Annotation effort
The training and annotation process required a total of 450 h.Each annotator was employed for 150 h.In particular, the annotators were asked to annotate for a maximum of 1 h per session to reduce errors due to fatigue or boredom from the repetitive task.The project leader coordinated the annotation work for a total of another 150 h.In total, the whole process required 6 months to be carried out.Additional effort was required to setup the annotation tool and to write down the first version of the guidelines.

The robotic-surgery PropBank
Both the framebank and the dataset resulting from the annotation process described in Sects.3.1 and 3.2 are publicly available. 10This section presents and discusses some statistics about them.In more detail, Sect.4.1 presents the RSPF, while 4.2 the annotated dataset.

The framebank (RSPF)
Using the method described in Sect.3.1, 252 lemmas have been analysed.At least one modification among those described in Sect.3.1.1have been requested in 109 cases.In particular, of the 252 analysed lemmas, 24 belong to MISSING_LEMMA case, i.e., new lemmas (verbs or nouns) that describe very specific actions of the surgical domain not yet present in the original PropBank have been added.22 lemmas belong to MISSING_FRAME case, i.e., new senses have been added to existing lemmas describing meanings not already covered by PropBank.Finally, 63 lemmas suffer of MISSING_ROLE problem, and thus corresponding existing predicate's sense has been enriched with new semantic roles frequently used in robotic-surgery.Considering both the new lemmas added, new frames added to existing lemmas and the new core roles added to existing frames, a total of 244 core roles have been added.They are able to describe the surgical sense of the corresponding lemma in finer granularity.Table 3 shows the semantic type of core roles added for the robotic-surgical domain lemmas.The table considers all core roles added, both in existing frames and in new frames: while the number of core roles added in the first row of the table is quite high, most The nature of the semantic roles inserted highlights that, in the surgical procedural language, it is of utmost importance to indicate for each action that describes an operation, who or what performs the action (Arg0), the anatomical part that undergoes the action (often Arg1), the instrument with which to perform the action, the surgical technique to adopt, the purpose, and a series of spatial information that helps locate the target anatomy within the human body.Overall, the number of newly introduced and modified lemmas and frames indicates that the extension of PropBank to cover the robotic-surgical domain is substantial and that procedural surgical language differs from general English in terms of both predicates used and roles required.

Dataset-level statistics
By following the annotation process and guidelines described in Sect.3.2, the first annotated dataset specific for SRL of robotic-surgery textbooks was obtained.28 different surgical operative descriptions have been annotated, for a total of 1,559 sentences and 32,448 tokens.The obtained dataset is composed of 12,202 annotations.Of  5 Arguments-level annotations.The pie-chart in the center shows the distribution of semantic arguments between modifier, core and references in our annotated dataset.In total, annotated 5,777 core arguments, 2,759 modifier arguments and 65 referent of other core arguments them, 3,601 are predicate-level annotations, and 8,601 are argument-level annotations, both core and modifier.Figure 5 shows more detail about the distribution of core and modifier arguments of this dataset.An high percentage of the modifier arguments (left side of the figure) in the annotated dataset is covered by TMP.It provides temporal relationships between predicates and thus it is useful to give a chronological order to the actions that must be performed for a correct execution of the robotic-surgical procedure.There are also many tokens annotated with the MOD label: mostly tokens likes "can", "must", "might", "may", "would" are annotated in this way.Specifying these arguments is useful for extracting information on the mandatoriness of surgical actions, or events that may occur in certain circumstances.Finally, other frequent modifier arguments are MNR, which enrich the corresponding predicate with generic information about the manner with which an action should occur, and ADV which in our dataset mostly identifies span of texts containing conditional operators (if, then, else or otherwise).The identification of spans of text tagged with this label is important for the automatic reconstruction of a workflow from text, i.e., to represent the surgical process in a more structured and schematic way.The remaining arguments describe spatial, purposeful, or other information not labeled with any core role.
Among the core arguments present in the dataset (right side of the figure), the most frequent is Arg1.Unlike the other core arguments, it has a well-defined semantics.It plays the role of patient, i.e., the object that undergoes the action described by the predicate to which it belongs.Also Arg0 has a well-defined semantics in most verbs, (i.e., the agent who performs the action described in the corresponding predicate), but it is not so frequent in this dataset.This observation was also made in (Wang et al., 2013): in most cases, the agent did not occur in sample sentences as most actions in procedural language are described in a passive voice, and the agent in operative notes, or procedural textbooks, that is typically the surgeon, the assistant, or the robot, is omitted from the text.For the core arguments of higher number, there is not a well-defined semantics, since it varies according to the frame considered.However, Arg2, Arg3 and Arg4 are also frequent, and they are often associated with the surgical instrument, technique or spatial information.
The statistics reported in this section confirm that a procedural surgical description is typically composed of the specification for each action of an agent, a patient, a surgical instrument or technique, spatial information and other procedural attributes (e.g., temporal information and purposes).

Procedure-level statistics
As stated before, 28 different robotic-surgery descriptions have been annotated.The average number of sentences per procedure is approximately 56.The shorter description is 10 sentences long, while the longer is composed of 123 sentences.These values are very different from that of other procedural descriptions.For example, in (Mysore et al., 2019) a dataset of nano-material syntesis procedural descriptions is presented, and they reported 9 sentences per procedure on average.In (Zhang et al., 2012), procedural corpora about kitchen and automotive domains were presented, and an average of 12 sentences per description was reported.This means that the robotic-surgical procedures described in textbooks can be much longer and detailed than the procedural descriptions of other domains and sources, at least the ones considered so far in the literature.
Finally, our procedures have a mean of approximately 129 predicates (with a minimum of 21 and a maximum of 257) and are composed of a mean of 1,161 tokens (with a minimum of 201 and a maximum of 2,457).

Sentence-level statistics
A sentence of the robotic-surgery procedural domain has 2.31 predicates on average (minimum is 1 and maximum is 9) and is composed of 5.52 arguments on average (minimum is 1 and maximum is 20).Finally it has 20.81 tokens on average (minimum is 5 and maximum is 81).This last value can be compared with (Mysore et al., 2019), where the authors observed that a sentence for nano-material synthesis has 26 tokens on average, and with (Zhang et al., 2012), where the authors reported that a procedural sentence of the kitchen or automotive domain is composed of 12 tokens on average.Also this comparison suggests that depending on the domain, author, source, and purpose, there exist more or less complex procedural sentences, and those from robotic-surgery textbooks tend to be among the most complex ones.

Predicate-level statistics
In total, this dataset uses 452 different predicates labels.Of them, 410 are used with only one sense, while 42 can be used with different meanings.In more detail, 100% of MISSING_LEMMA lemmas are monosemous, meaning that there are not multiple surgical senses for very specialized, domain lemmas; furthermore, approximately 70% of MISSING_FRAME lemmas and 85% of MISSING_ROLE lemmas are used with only one sense in our dataset.These statistics show that the procedural surgical language makes extensive use of monosemous predicates.Furthermore, even for lemmas with multiple senses available in RSPF, one of them is typically used much more frequently in the robotic-surgery domain than all the other senses.More in details, for each predicate p present in the dataset with at least two different meanings, denoting with α p the frequency of the most common sense for the analysed predicate with respect to the total number of occurrences in the dataset, we observe that α p is on average 0.77: that is, the most frequent sense is used in almost 8 times out of 10 of the occurrences of that predicate in the dataset, confirming that also for polysemous RSPF lemmas, only one sense is mainly used in the dataset.Table 4 shows examples of predicates, with the specification of the number of senses with which they appear in the dataset, together with the information on the most frequently used sense and the corresponding percentage of occurrence.
Finally, from a tenses point of view, approximately 56% of annotated predicates are in passive or past tense, 25% are in a present or imperative tense, 14% in present participle or gerund form and 5% in a nominalized form.This states that the most common way to describe a surgical procedure is by using the passive, past, imperative or present tenses.

Preliminary experiments with the obtained dataset
To confirm the need of adapting PropBank to better support information extraction and NLU within the robotic-surgery domain, a preliminary assessment was performed, to estimate how many of the dataset sentences would be wrongly or incompletely annotated by a state-of-the-art SRL tool, trained on PropBank and general English text, due to missing robotic-surgery specific information in the original PropBank: • ∼36% of the sentences contains at least an action (with a corresponding frame in PropBank) and the mention of a domain-specific semantic role not in PropBank (MISSING_ROLE); • ∼21% of the sentences contains at least an action describing a different meaning than the ones covered by its frames in PropBank (MISSING_FRAME); • ∼2% of the sentences contains at least an action whose lemma is not in PropBank (MISSING_LEMMA); • the remaining sentences (∼41%) could be fully annotated with information already contained in PropBank (PRESENT).
That is, more than half of the sentences would need some information covered by RSPF, but missing in PropBank, to be properly annotated.
To complement this investigation, we processed the contributed annotated dataset with a state-of-the-art, transformer-based, general-English SRL tool (Li et al., 2020), and compared the automatically provided annotations (the tool was trained only on the catalogue of frames and role in PropBank) with the manual ones (which comprise frames and roles also in RSPF).More in details, we measured the capability of the tool to correctly identify and disambiguate the semantic roles of the predicates, the standard measure used to assess SRL performance, obtaining an F1-score of 0.701.On general English text (CoNLL-05, CoNLL-12), the same tool achieves an F1-score above 0.87.This substantial difference confirms once again that the robotic-surgical language is noticeably different than the general English one, and that state-of-the-art SRL tools achieve a much lower performance score when applied on very specific domain, than the ones reported on standard general English benchmarks.
Performance can be substantially improved by leveraging our robotic-surgical annotated data also as training material to fine-tune available general-English SRL models.Indeed, when fine-tuning the aforementioned SRL model on RSPB, thus making aware the model of the RSPF frames and roles and their usage, the F1-score on identifying and disambiguating the semantic roles raises to 0.762 (i.e., +0.061 over the performance without fine-tuning).Further experiments and assessments on exploiting RSPB with various SRL models for extracting surgical actions and their arguments are reported and discussed in details in Bombieri et al. (2023).

Conclusions and future works
In this paper, we presented the first annotated resource for improving robotic-surgical natural language understanding.The dataset consists of a corpus collecting sentences from textbooks and academic papers, describing different robotic-surgical procedures, that have been manually annotated in a PropBank-style exploiting an extension of its framebank, i.e., the catalogue of frames and roles, for the robotic-surgical domain.In details, the construction of the dataset followed two steps: in the first one a framebank specific to the surgical domain (RSPF) has been defined.In the second step, RSPF was applied to manually annotate sentences, taken as-is without modification, from roboticsurgical texts.The annotation was performed at two levels: predicate-level, where predicates are identified and disambiguated with respect to RSPF, and arguments-level, where the same tasks are performed for the semantic arguments of each predicate.To perform the annotation, a team of collaborators with different roles has been setup: two annotators, one project-leader, and one clinician for a final validation.The annotators were duly trained on PropBank, SRL, and RSPF, both with theoretical workshops and with an iterative training process described in the paper.The resulting resource (RSPF and annotated dataset) is publicly released, to foster further research in this direction and to enable benchmarking of SRL tools in the robotic-surgery domain, yet little-explored for natural language understanding.
As a work, following up some preliminary work presented in Bombieri et al. (2023), we will leverage the annotated dataset to compare different machine learning methods.We aim to show how these annotations can be used, not merely to improve natural language understanding models for the surgical domain, but also for developing knowledge-based smart clinical applications.We will also work on further the resource with new annotations.

Fig. 1
Fig. 1 High level diagram of the method described in Sect.3.1.4for the framing of surgical domain verbs and annotation

Fig. 2
Fig.2XML file for the "approximate" lemma.It contains the number of the frame (02), with its informal definition (to come near in position, to bring near).It then enumerates a list of semantic core roles (numbered from 0 to 4) and provides an annotation example

Fig. 4
Fig. 4 On top, annotation example of one sentence through Inception tool graphical interface.In red are predicate annotations while in yellow arguments related to the corresponding predicate.The annotation is finally exported in CoNLL-2012 format and it is directly processable by state-of-the-art SRL tools.Of the CoNLL-2012 fields, only the following columns have been annotated: the 3rd (identification number of the token), the 4th (list of tokens in the sentence), the 7th and 8th (predicate and corresponding frame number) and from the 12th to the second-last containing CoNLL-2012 annotations.In this sentence, three predicates are present: the first (minimize.01)is linked with only one argument (Arg1), the second (place.01)with two (ArgM-PRP, Arg1 and Arg2) and the third (place.01)with two (Arg1 and Arg2) whose meanings are contained in the RSPF.(Color figure online) Fig.5Arguments-level annotations.The pie-chart in the center shows the distribution of semantic arguments between modifier, core and references in our annotated dataset.In total, annotated 5,777 core arguments, 2,759 modifier arguments and 65 referent of other core arguments

Table 1
Categories to which each of the candidate lemmas is assigned to

Table 2 (
Left) Example of nominalized actions extracted using the method described in Section 3.1.3with indication of the verb they refer to ("-" means missing corresponding verb) and the modification required.(Right) Example domain lemmas extracted using the method described in Sect.3.1.4with indication of the type of modification required MISSING_ROLE> < Incise , MISSING_ROLE >

Table 3
Semantic type of the core roles added to modified lemmas

Table 4
Examples of 10 different predicates with the indication of the number of senses with which they appear in the dataset (S. in text), the number of senses in the RSPF (S. in RSPF), and the reference to the most frequently used sense with the corresponding percentage of occurrence