Revisiting the ISO - T ime ML abstract syntax (2025)

Abstract: This paper describes some of the ongoing work within the ISO preliminary work item PWI 254617-17, ‘Interlinking of annotations’. This PWI investigates the possibilities and problems of combining annotations made with different annotation schemes. using the ‘interlinking’ approach (Bunt, 2024) applied to different parts of the multi-part standard ISO 24617, ‘Semantic annotation framework’. This paper focuses on the combination of ISO-TimeML and QuantML at the level of abstract syntax. A new version is defined for the ISO-TimeML abstract syntax specification and how it relates to the concrete (XML-based) syntax as a basis for this combination. As a side-effect, some issues in the use of ISO-TimeML come to light that could be relevant for a possible future second edition of this standard.

## introduction developing the semaf standard as a set of separate sub-standards has proved useful, as it is better feasible to develop an annotation schema for a welldelineated semantic domain. the first two parts of semaf, informally known as 'iso-timeml' and 'diaml', are successful examples of the application of this approach, as the annotation of time and events is clearly separable from the annotation of dialogue acts. however, some of the semantic do-mains are not entirely disjoint; some semantic phenomena play a role in more than one sub-standard. for example, the expression "every monday" quantifies over mondays. being a temporal expression, iso-timeml provides an annotation of this expression, including an indication of its quantifying character. iso-timeml has only a rudimentary treatment of quantification, however @xcite , while it is the focus of semaf part 12, quantml this paper reports on activities within the iso preliminary work item pwi 254617-17, interlinking of annotations. this pwi investigates the possibilities and problems of combining annotations made with different annotation schemes, using the interlinking approach introduced in @xcite . in particular this approach seems interesting for combining annotations made according to different parts of semaf, which focus on different types of semantic information. on this approach, links are added between elements of different annotations for indicating that these elements correspond to the same entities mentioned in the primary data. this allows annotations of the same entities with different types of information, and therefore facilitates the merge of the semantic information in the respective annotations. when considering the combination of annotations from different semaf parts, we have to consider all three interrelated levels distinguished in the architecture of a semaf scheme (see fig. 1 ): (1) the concrete syntax, conventionally with an xmlbased reference format, (2) the abstract syntax, expressing the semantically relevant information of the annotations in the form of pairs, triples, and other set-theoretical structures (and interrelated with the concrete syntax through encoding and decoding functions), and (3) the semantics of the annotations. at the level of concrete syntax, interlinking consists of adding identity links between components of representations from different schemes, indicating that the same stretch of primary data is annotated from different points of view. at the level of abstract syntax, the structures of the interlinked annotations are combined into a single set-theoretical structure. at the level of semantics, finally, the semantic interpretation function describes the meaning of the joint abstract syntax expressions. at the level of concrete syntax, the addition of identity links between two (or more) representations is a straightforward matter, although there may be some issues in the identification and use of markables, but the real challenges lie at the levels of abstract syntax and semantics. in particular, sitting in between the levels of concrete representation and semantics, the combination of annotations at the level of abstract faces a dual challenge. on the one hand, the expressions at that level should have a systematic encoding-decoding relation to each of the respective concrete representations, and on the other hand they should capture the information contained in the combined annotations in a way that allows their joint semantic interpretation. since iso-timeml (iso-24617-1:2012 time and events) and quantml (iso 24617-12:2025 quantification) are two of the best developed and most complex semaf parts, a sensible strategy would seem to first explore the possibilities of combining their respective annotations, in particular at the level of abstract syntax. quantml has a fully developed abstract syntax, but iso-timeml, being the oldest semaf part, has an abstract syntax that is not fully specified and at some points lacks conceptual clarity. this paper therefore revisits the iso-timeml abstract syntax, aiming to develop a full, conceptually clear specification for the concrete (xml-based) representations as they are. section 2 takes a step in that direction. since the abstract syntax is required to allow systematic decoding of concrete representations, the adequacy of any revised version can be tested by specifying the decoding function. section 3 is therefore devoted to the mapping of concrete representations to expressions of the abstract syntax. section 4 indicates the next steps towards fully specified interlinked iso-timemml-and quantmlannnotations. formulating a version of the abstract syntax and the semantics of iso-timeml in the same style as quantml 1.2 iso-timeml iso-timeml distinguishes three types of temporal objects: instants, dates, and periods. with respect to instants, the iso 24617-1:2012 specification document notes that in reality, nothing happens in infinitesimally small time; every event or state that occurs in reality (or in someone's mind) requires more than zero time, although natural languages offer speakers the possibility to express themselves as if something occurs at a precise instant (as in "i will call you at twelve oclock". such an instant is often associated with the beginning of an event, as in this example. the explicit mentioning of the start of an event, as in "i was sad when mary started to cry", illustrates the same phenomenon. punctual events are associated with precise instants, as in the example "gates will close at 9:25." the notion of a precise instant is similar to that of a point in mathematics. euclid defined a point as a spatial entity that which has no parts. in other words, a point is an indivisible spatial object with zero length, breadth, and height. natural language speakers refer to instants as points on a timeline, as intervals of zero length, even though they probably know that such intervals do not really exist. in everyday language, instants are referred to with the precision of minutes, as in "its five past twelve". it is therefore appropriate to consider such intervals as instants in the iso-timeml abstract syntax. fully specified references to instants consist of a (fully specified) date and time. a fully specified date contains the specification of (1) a year, (2) a month and (3) a day number, or (2) a week number and a (3) day name. in practice, reference to instants is often underspecified, such as "monday at two", intended to be understood as next monday at two p.m. or as last monday at two p.m. depending on the context (which also allows to infer the year and the week). underspecification is represented in iso-timeml by using the character 'x' in values of the @value attribute. (examples below.) instants are annotated in the iso-timeml reference representation format @xmath0; dates by expressions of type "date"; periods by expressions with @@xmath1. from a semantic point of view, year numbers, calendar month names, and day names function like proper names. just like "james" refers to a contextually particularly salient person named james, "tuesday" refers to the contextually most salient day named 'tuesday'. year numbers ("1984") refer to certain time intervals independent of context, just like country names ("denmark", "japan") refer to geopolitical regions independent of context. the specification of the iso-timeml abstract syntax is best done with (a) the semantics in mind and (b) specifying the decoding function that relates it to the concrete syntax -which in turn calls for a precise specification of optional attributes and default values in the concrete syntax. in @xcite several forms of optionality are distinguished: (a) semantic, i.e. a certain type of annotation structure may contain such a component, but does not have to for being interpretable; (b) a component that does not have to be specified in the concrete syntax, since it has a default value in the abstract syntax; (c) a component in the concrete representation that has no semantic interpretation. these distinctions are useful for a clear formulation of the abstract syntax in relation to the concrete syntax and semantics. @xmath2, <@xmath3. for example, the @relatedtoevent attribute @xmath4, and vice versa. also, the attributes @tense and @aspect @xmath5, and @beginpoint is applicable only if @@xmath6. the possible values of the @reltype attribute @xmath7. the value "identity" is unusual in this respect, as it designates the identity of two events, rather than a temporal relation; it would seem to entail the temporal relation simultaneous. it may be noted that simultaneous, after and before are all instances of the discourse relations synchrony and asynchrony, defined in the iso standard for annotating discourse relations @xcite . the conditional applicability of various attributes in elements of the concrete syntax means, in the 3layer architecture of semaf parts, that alements @xmath8, can correspond to several different structures in the abstract syntax. as in the case of other semaf parts, the abstract syntax of iso-timeml has two components: (1) the specification of a store of primitive concepts, called the conceptual inventory, and (2) the recursive specification of the annotation structures that may be formed by combining primitive concepts or annotation structures to form set-theoretic structures like pairs and triples. the structures defined by the abstract syntax come in two forms: (a) entity structures, i.e., structures that contain semantic information about a stretch of source data (a markable), and (b) link structures, which express semantic relations between two or more entity structures. an entity structure has the form of a pair markable, semantic information ; a link structure has the form 'entity structure 1, entity structure 2, .. entity structure n , semantic relation . entity structures are represented in the concrete syntax by xml elements that have a @target attribute whose value refers to the relevant stretch of source data. ## next steps and issues for further study revisiting the iso-timeml abstract syntax, we are in fact applying the cascades method for developing or improving an annotation schema (pustejovsky, @xcite . this means that the specification of an annotation scheme consists of four consecutive stages: (1) establishment of a metamodel, (2) -(3) specification of concrete and abstract syntax and the decoding function that connects them, (4) definition of semantic interpretation. feedback loops go back from any stage to any previous stage. in reverse engineering mode, one can start at any of the four stages and follow steps forward or backward to ensure inter-stage consistency. in the case of revisiting the iso-timeml abstract syntax, we take the existing concrete syntax and the metamodel on which it is loosely based for granted. starting at the abstract syntax stage (3), the next step forward is the specification of the semantics; the most relevant feedback step is ensuring the consistency between abstract and concrete syntax, which is accomplished by specifying a decoding function. regarding the next step forward, we have started the definition of a revised compositional semantics for the expressions of the (revised) abstract syntax as outlined above. inspired by the specification of the semantics of quantml (see @xcite , this semantics takes the form of a recursive function that interprets annotation structures as second-order drss @xcite . regarding the next step backward, while specifying the decoding function we have noted some unclear aspects, limitations and gaps in the concrete syntax as specified in iso 24617-1:2012 and in the guidelines for its use. this could be of interest for a possible future update of the specification and the guidelines. some these issues are the following. 1. in iso-timeml, periods are assumed to be contiguous. this is not always realistic, in view of sentences such as "i studied from nine to five" -there must have been interruptions in this interval. this calls for the introduction of possibly discontinuous intervals. as the examples in section 3.3 illustrate, <@xmath9, whose value refers to @xmath10. this attribute seems semantically superfluous, since its @pred value, which specifies the temporal relation, is also expressed in the value of the @reltype attribute in @xmath11. most importantly, the outcome of this study is a version of the iso-timeml abstract syntax and the decoding function from concrete to abstract syntax that promise to provide a solid basis for the further interlinking of iso-timeml annotations and quantml annotations.