Time Ontology Extended for Non-Gregorian Calendar Applications
Simon J D Cox CSIRO Land and Water, PO Box 56, Highett, Vic. 3190, Australia [email protected]
Abstract.
We extend OWL-Time to support the encoding of temporal position in a range of reference systems, in addi- tion to the Gregorian calendar and conventional clock. Two alternative implementations are provided: as a pure extension or OWL-Time, or as a replacement, both of which preserve the same representation for the cases origi- nally supported by OWL-Time. The combination of the generalized temporal position encoding and the temporal interval topology from OWL-Time support a range of applications in a variety of cultural and technical settings. These are illustrated with examples involving non-Gregorian calendars, Unix-time, and geologic time using both chronometric and stratigraphic timescales.
Keywords: temporal reference system, calendar, temporal topology, ontology re-use
1. Introduction (defined as 1950 for radiocarbon dating [14]), or named periods associated with specified correlation OWL-Time [6] provides a lightweight model for markers [4,5,8]. the formalization of temporal objects, based on Al- Since OWL-Time only allows for Gregorian dates len’s temporal interval calculus [1]. Developed pri- and times, applications that require other reference marily to support web applications, date-time posi- systems must look elsewhere. However, the basic tions are expressed using the familiar Gregorian cal- structures provided by OWL-Time are not specific to endar and conventional clock. a particular reference system, so it would be prefera- Many other calendars and temporal reference sys- ble to use them in the context of a more generic solu- tems are used in particular cultural and scholarly con- tion. Some previous extensions to OWL-Time have texts. For example, the Julian calendar was used been proposed, in particular to deal with aggregates throughout Europe until the 16th century, and is still [10] and periodically recurrent intervals [13]. Perrin used for computing key dates in some orthodox et al. [11] use the OWL-Time temporal relations in Christian communities. Lunisolar (e.g. Hebrew) and their geologic timescale ontology, but introduce a lunar (e.g. Islamic) calendars are still used in some new class and property for geochronologic instants. communities, and many similar have been used his- In this paper we describe extensions to OWL-Time, torically. Dynastic calendars (counting years within which support eras defined by the reign of a monarch or dynasty) - the use of an explicit temporal reference system were used earlier in many cultures. In more contem- when specifying temporal position, porary applications, Loran-C, Unix and GPS time are - general encodings for dates and times not based based on seconds counted from a specified origin (in on the Gregorian calendar and clocks. 1958, 1970 and 1980, respectively). Archaeological We provide two implementations: “Time-plus” is a and geological applications use chronometric scales pure extension to OWL-Time, and “Time-new” is a based on years counted backwards from ‘the present’ generalized replacement1, which preserves the core cision of seconds or finer indicated by the precision of OWL-Time within a modified class hierarchy. of the seconds field in the value. Using the class We illustrate the application of the ontology with a time:DateTimeDescription temporal position is given number of examples. While we do not provide a as a value structured using separate properties, with model for describing temporal reference systems, we precision in the range from seconds to years, indicat- 2 show how the extended ontology supports the de- ed by the value of the time:unitType property . The scription of ordinal temporal reference systems also properties time:year, time:month and time:day have extending into deep time. range xsd:gYear, xsd:gMonth and xsd:gDay respective- ly, which are tied to the Gregorian calendar [3,12]. In order to support a wider range of temporal posi- 2. Time-plus - extension to OWL-Time tion descriptions, in Time-plus we introduce two classes - tplus:GenDateTimeDescription and 2.1. Temporal reference system tplus:TimePosition. The former is a generalization of time:DateTimeDescription, with the range of A useful classification of temporal reference sys- tplus:year, tplus:month and tplus:day properties tems is provided in ISO 19108 [7]. Four kinds of adapted for use with non-Gregorian calendars. In system are distinguished: tplus:TimePosition, two properties provide alterna- - Coordinate systems, in which a (temporal) po- tive encodings for the value: tplus:numericValue for sition is expressed as a signed quantity, offset position described using a number, and from a specified origin tplus:nominalValue for position indicated as a name. - Ordinal reference systems, based on ordered The property tplus:hasTRS (described above) is man- named intervals datory on individuals from both classes, to indicate - Calendars, in which position is expressed us- the reference system. We also introduce properties ing a year-month-day structure tplus:inDateTime and tplus:inTimePosition as alter- - Clocks, in which position within a day is ex- natives to time:inDateTime and time:inXSDDateTime pressed in hours-minutes-seconds. provided in OWL-Time. The new classes and proper- The temporal reference system used in OWL-Time ties are summarized in Table 1, with relationships to is not explicitly specified [6], but can be inferred to OWL-Time shown in Figure 1. be the Gregorian calendar and conventional clock as These extensions allow temporal position to be this is specified for the xsd:dateTime, xsd:gYear, specified using all temporal reference system types: xsd:gMonth and xsd:gDay datatypes used in encoding - A temporal coordinate using a values [3,15]. tplus:TimePosition with a tplus:numericValue In Time-plus we introduce an additional property, - An ordinal position using a tplus:TimePosition denoted tplus:hasTRS, to support explicit indication with a tplus:nominalValue of a temporal reference system. Its range is the class - A position in the Gregorian calendar using of temporal reference systems, denoted tplus:TRS. As time:DateTimeDescription with time:unitType set defined in this ontology, this class is a stub that is to time:unitDay only a placeholder for the top of a hierarchy of tem- - A position in an arbitrary calendar using poral reference system types, so no properties are tplus:GenDateTimeDescription with defined with the domain tplus:TRS, and there are no time:unitType set to time:unitDay local restrictions. - A position in a calendar/clock system using either - time:DateTimeDescription or 2.2. Temporal position tplus:GenDateTimeDescription with time:unitType set to time:unitHour, Two encodings for temporal position are provided time:unitMinute or time:unitSecond, in OWL-Time. Using the datatype xsd:dateTime, - xsd:dateTime with the default reference sys- position is encoded as a structured literal, with a pre- tem. The range of tplus:nominalValue in the context of
the generalized tplus:TimePosition is a string, since 1 The time-plus ontology is published at http://def.seegrid.csiro.au/ontology/time-plus and time-new the requirement is to support designation of position at http://def.seegrid.csiro.au/ontology/time-new. Elements 2 of the ontologies are denoted in this paper with the Resources from OWL-Time are denoted in this namespace prefixes tplus: and tnew:, respectively. paper with the prefix “time”. in any ordinal reference system, the full set of which a particular calendar, the lexical representations will is not known (e.g. ‘beginning of Late Cambrian’, not support strict value-based reasoning in generic ‘end of the bronze age’, ‘end of Ming dynasty’, ‘start OWL processors. of the reign of Pope Leo IX’). Listing 1 – definition of tplus:genMonth as a string pattern (Turtle The range of each generalized date property is de- syntax [2]) fined using the datatype restriction capability of tplus:genMonth a rdfs:Datatype ; OWL2 [9] so that it has the same lexical form as the rdfs:label "Generalized month"^^xsd:string ; original property used in OWL-Time (except that owl:onDataType xsd:string ; permitted month values go up to 13 because some owl:withRestrictions ( [ xsd:pattern "--(0[1-9]|1[0-3])(Z|(\\+|-)((0[0-9]|1[0-3]):[0-5][0- lunisolar calendars, such as Hebrew, use a leap- 9]|14:00))?"^^xsd:string ] ) . month). For example, the definition of tplus:genMonth is shown in Listing 1. However, since the new date datatypes are not constrained to refer to
Table 1 – Elements of the ontology
Classes tplus:TRS tplus:GenDateTimeDescription tplus:TimePosition Properties tplus:hasTRS domain tplus:TimePosition|tplus:GenDateTimeDescription range tplus:TRS tplus:inDateTime domain time:Instant range tplus:GenDateTimeDescription domain tplus:GenDateTimeDescription tplus:day range tplus:genDay tplus:month range tplus:genMonth tplus:year range tplus:genYear tplus:inTimePosition range tplus:TimePosition domain tplus:TimePosition tplus:numericValue range tplus:Number tplus:nominalValue range xsd:string Datatypes tplus:genDay String with pattern constraint matching lexical representation of tplus:genMonth xsd:gDay|xsd:gMonth|xsd:gYear tplus:genYear tplus:Number set of numbers
Figure 1 – Extended time ontology for supporting additional temporal position encodings. Resources from OWL-Time use the namespace prefix “time:”. (UML-style representation of classes and properties from TopBraid.)
Listing 2 – Local constraints on values of day, month and year 3. Time-new - generalization of OWL-Time properties in the context of a Gregorian date-time description tnew:DateTimeDescription a owl:Class ; The Time-plus ontology described above extends rdfs:subClassOf tnew:GenDateTimeDescription ; OWL-Time non-intrusively. However, while the rdfs:subClassOf [ a owl:Restriction ; owl:allValuesFrom xsd:gDay ; class tplus:TimePosition adds distinct new function- owl:onProperty tnew:day ality, the class tplus:GenDateTimeDescription merely ] ; clones time:DateTimeDescription, with the ranges of rdfs:subClassOf [ a owl:Restriction ; owl:allValuesFrom xsd:gMonth ; the three date properties generalized, plus a mandato- owl:onProperty tnew:month ry tplus:hasTRS property. A more natural implemen- ] ; rdfs:subClassOf [ a owl:Restriction ; tation would recognize that the membership of owl:allValuesFrom xsd:gYear ; time:DateTimeDescription is a subclass of owl:onProperty tnew:year tplus:GenDateTimeDescription. ] ; rdfs:subClassOf [ a owl:Restriction ; We have used the latter approach in Time-new, owl:hasValue which is summarized in Figure 2. The class
Figure 2 – Generalized time ontology for supporting additional temporal position encodings.
end of the dinosaurs is given as a named position 4. Examples within the international chronostratigraphic chart [5]. Listing 5 shows how the extended ontology sup- Listing 3 provides an example of a time instant ports the description of elements in an ordinal tem- with position formalized in four different ways, using poral reference system. The Cambrian Period is Time-plus: modeled as a time:ProperInterval. The beginning - time:inXSDDateTime shows the date and time and end are modeled as time:Instants, whose posi- encoded in compact form using the standard tions are given as temporal coordinates in millions of datatype derived from ISO 8601 years counted backwards, using the new - my:AbbyBirthdayGregorian encodes the date and tplus:TimePosition class. Topological relations with time according to the Gregorian calendar using other Eons, Periods and Epochs are described using separate properties for its elements the properties provided in OWL-Time (non- - my:AbbyBirthdayHebrew encodes the date and exhaustively). time according to the Hebrew calendar using Using the Time-new ontology, these examples will separate properties for its elements be structurally identical, but with the prefixes time: - my:AbbyBirthdayUnix encodes the birthday and and tplus: both replaced by tnew:, and time as a temporal coordinate, specifically as the tplus:genYear, tplus:genMonth and tplus:genDay in integer number of seconds since the epoch 1970- Listing 3 replaced by suitable datatypes defined for 01-01T00:00:00.00Z. the Hebrew calendar. Listing 4 provides two examples of events in geo- Note that in both Time-plus and Time-new, the logic time. The time of formation of the earth is giv- cases supported by OWL-Time are represented iden- en as a coordinate in the reference system that counts tically to the original. This was a key design goal of years backwards from the present. The time of the the new ontologies.
Listing 3 – A single event with temporal position encoded in multiple temporal reference systems my:AbbyBirthday rdf:type time:Instant ; tplus:inDateTime my:AbbyBirthdayHebrew ; tplus:inTimePosition my:AbbyBirthdayUnix ; rdfs:label "Abby's birthdate"^^xsd:string ; time:inDateTime my:AbbyBirthdayGregorian ; time:inXSDDateTime "2001-05-23T08:20:00+08:00"^^xsd:dateTime ; . my:AbbyBirthdayGregorian rdf:type time:DateTimeDescription ; time:day "---23"^^xsd:gDay ; time:dayOfWeek time:Wednesday ; time:hour "8"^^xsd:nonNegativeInteger ; time:minute "20"^^xsd:nonNegativeInteger ; time:month "--05"^^xsd:gMonth ; time:timeZone [ rdf:type tzont:TimeZone ; tzont:GMToffset "+8" ; tzont:name "AWST" ; ] ; time:unitType time:unitMinute ; time:year "2001"^^xsd:gYear ; . my:AbbyBirthdayHebrew rdf:type tplus:GenDateTimeDescription ; tplus:day "---01"^^tplus:genDay ; tplus:month "--03"^^tplus:genMonth ; tplus:hasTRS
Listing 4 – Events in geologic time encoded using a deep-time coordinate, and using a named element from the geologic timescale geotime:FormationOfEarth rdf:type time:Instant ; tplus:inTimePosition [ rdf:type tplus:TimePosition ; tplus:numericValue "4.567e9"^^tplus:Number ; tplus:hasTRS
geotime:EndOfDinosaurs rdf:type time:Instant ; tplus:inTimePosition [ rdf:type tplus:TimePosition ; tplus:nominalValue "Base of Cenozoic"^^xsd:string ; tplus:hasTRS
Listing 5 – Elements from the geologic timescale, showing some topological relations geotime:Cambrian rdf:type time:ProperInterval ; rdfs:label "Cambrian period"^^xsd:string ; time:hasBeginning geotime:BasePhanerozoic ; time:hasEnd geotime:BaseOrdovician ; time:intervalAfter geotime:Precambrian ; time:intervalBefore geotime:Mesozoic ; time:intervalBefore geotime:Ordovician ; time:intervalBefore geotime:Silurian ; time:intervalContains geotime:CambrianSeries2 ; time:intervalContains geotime:CambrianSeries3 ; time:intervalFinishedBy geotime:Furongian ; time:intervalMeets geotime:Ordovician ; time:intervalMeets geotime:Precambrian ; time:intervalStartedBy geotime:Terreneuvian ; time:intervalStarts geotime:Paleozoic ; time:intervalStarts geotime:Phanerozoic ; . geotime:BaseOrdovician rdf:type time:Instant ; tplus:inTimePosition geotime:BaseOrdovicianTime ; rdfs:label "Base of Ordovician Period"^^xsd:string ; . geotime:BaseOrdovicianTime rdf:type tplus:TimePosition ; tplus:numericValue "485.4"^^tplus:Number ; tplus:hasTRS
Turtle, World Wide Web Consortium, 2014, Available at: 5. Summary http://www.w3.org/TR/2014/REC-turtle- 20140225/. We have introduced a small extension to OWL-Time to support description of temporal position with an [3] P. V. Biron, A. Malhotra, XML Schema Part explicit temporal reference system, allowing use of 2: Datatypes Second Edition, Cambridge, temporal coordinate systems, ordinal temporal refer- Mass. USA, 2004, Available at: ence systems, and generalized calendars. The ontolo- http://www.w3.org/TR/xmlschema-2/. gy uses the interval topology from OWL-Time. The new ontology is implemented as a non-intrusive ex- [4] S.J.D. Cox, S.M. Richard, A formal model tension with three new classes, eight new properties, for the geologic time scale and global and four datatypes, or alternatively as a replacement stratotype section and point, compatible with for OWL-Time with a smaller total element count. geospatial information transfer standards, The primary complications arise from the involve- Geosphere. 1 (2005) 119 ment of datatypes from XML Schema that are tied to DOI:10.1130/GES00022.1. the Gregorian calendar, which must be generalized for use in a wider range of applications. Generalized [5] S.J.D. Cox, S.M. Richard, A geologic types for date-fragments are defined to match the timescale ontology and service, Earth Sci. familiar lexical productions from XSD, however, the Informatics. (2014) DOI:10.1007/s12145- value space for both these and the XSD types used in 014-0166-2. OWL-Time are not supported in OWL2, so no stand- ard reasoning support should be expected or relied upon when used in class descriptions. Apart from this, [6] J.R. Hobbs, F. Pan, Time Ontology in OWL, the new ontologies are capable of OWL2-conformant World Wide Web Consortium, 2006, encoding of temporal concepts used in a variety of Available at: http://www.w3.org/TR/owl- cultural and technical settings, covering all of the time/. temporal reference system types described in ISO 19108, but which retain exactly the same form as [7] ISO/TC-211, ISO 19108:2002 - Geographic OWL-Time for the cases handled by the original on- information -- Temporal schema, tology. International Organization for Standardization, Geneva, 2002, Available at: http://www.iso.org/iso/catalogue_detail.htm? Acknowledgements csnumber=26013.
This work is a contribution towards the harmoni- [8] X. Ma, P. Fox, Recent progress on geologic zation of W3C and Open Geospatial Consortium time ontologies and considerations for future standards for geospatial data, and was supported by works, Earth Sci. Informatics. 6 (2013) 31– the CSIRO Land and Water Flagship. Michael 46 DOI:10.1007/s12145-013-0110-x. Compton encouraged me to add the Time-new ontol- ogy to the paper, and David Ratcliffe provided advice [9] B. Motik, P.F. Patel-Schneider, B. Parsia, on some of the hairy datatyping issues. OWL 2 Web Ontology Language Structural Specification and Functional-Style Syntax (Second Edition), Cambridge, Mass. USA, References 2012, Available at: http://www.w3.org/TR/2012/REC-owl2- [1] J.F. Allen, Maintaining knowledge about syntax-20121211/#Datatype_Maps. temporal intervals, Commun. ACM. 26 (1983) 832–843 DOI:10.1145/182.358434. [10] F. Pan, A Temporal Aggregates Ontology in OWL for the Semantic Web, in: Proc. AAAI [2] D. Beckett, T. Berners-Lee, E. Fall Symp. Agents Semant. Web, 2005: pp. Prud’hommeaux, G. Carothers, RDF 1.1 30–37. [11] M. Perrin, L.S. Mastella, O. Morel, A. Lorenzatti, Geological time formalization: an improved formal model for describing time successions and their correlation, Earth Sci. Informatics. 4 (2011) 81–96 DOI:10.1007/s12145-011-0080-9.
[12] D. Peterson, S. (Sandy) Gao, A. Malhotra, C.M. Sperberg-McQueen, H.S. Thompson, W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes, Cambridge, Mass. USA, 2012, Available at: http://www.w3.org/TR/2012/REC- xmlschema11-2- 20120405/datatypes.html#gMonth.
[13] M. Poveda-Villalón, M.C. Suárez-Figueroa, A. Gómez-Pérez, A Pattern for Periodic Intervals, Semant. Web J. (2014) submitted.
[14] Radiocarbon magazine - Author guidelines. [Online]. Available at: https://journals.uair.arizona.edu/index.php/ra diocarbon/about/submissions#authorGuidelin es. [Accessed: 09-Sep-2014].
[15] ISO 8601:2004 - Data elements and interchange formats -- Information interchange -- Representation of dates and times, Geneva, 2004, Available at: http://www.iso.org/iso/catalogue_detail?csnu mber=40874.