In this paper we attempt to implement the temporal attributes of historical or archaeological objects in information systems by enhancing ISO 19108 standards.
There is no doubt about the importance of temporal attributes for humanities. And the standardization of temporal attributes is also important to utilize IT for integrating or exchanging data of humanities. From standardization’s point of view for the digital expression of temporal attributes, there are some discussion points about the characteristics of them, which is from semantic concepts to encoded formats. CIDOC/CRM (its official standard is ISO 21127) defines the semantic model of heterogeneous cultural heritage information, and contains the temporal element as “E2 Temporal Entity”, “E51 Time Span”, “E62 Time Primitive” and so on. These semantic common class definitions are valuable for the application area of cultural heritage and museum documentation, however CIDOC/CRM does not approach to build a general concept of temporal attributes for information resources of humanities, nor cover the encoding specifications of each class. A standardized implementation specification for E15 or E62 of CIDOC/CRM has to be required, and our study is positioned there.
There are currently two major international standards for common temporal attributes. One is ISO 8601 titled “Data elements and interchange formats – Information interchange – Representation of Dates and Times”, which is based on Gregorian calendar and Coordinate Universal Time (UTC). For example, the format of “2011-03-11” is conformed to ISO 8601. It is widely used in representing date or time on information system. Although it provides convenient representation forms for recent events or activities, it is not suit for describing historical events, as they sometimes cannot be applied Gregorian calendar, and are required to use complex temporal expressions.
The other is ISO 19108 “Geographic information – Temporal schema”, which defines the schema in order to implement many types of calendars or eras. It also defines the ordinal era to support the Jurassic period or the Cretaceous period, that are classified the order of periods. In contrary to ISO 8601, it can potentially support complex temporal expressions. In addition, ISO 19108 links to other encoding specifications in the same standards family. ISO 19118 “Geographic information – Encoding” provides basic encoding rules and ISO 19136 “Geographic information – Geography Markup Language” provides a practical encoding specification based on XML.
“<gi:date8601>2011-03-11</gi:date8601>” and “<gi:ordinalPosition idref="NaraPeriod"/>” are core parts of XML encoded examples conformed to ISO 19108 and ISO 19118.
ISO 19108 defines the common data model for temporal characteristics with varieties of temporal expressions. However, it is not sufficient to express the temporal attributes of humanities’ objects, especially for historical or archaeological objects. Because these objects sometimes cannot be assigned the year of existence in any calendar, they sometimes use originally defined period or era, whose start or end time of their time span sometimes cannot specify clearly. Then, we considered following cases of expressions: 1) Century 2) Age, Era, Period 3) Stage, Phase, Subperiod 4) Ambiguous temporal expression 5) Cyclical temporal expression. We have implemented above five cases with enhancements of ISO 19108 specifications, as follows. (In following cases, class names that start with “TM_” are from ISO 19108)
For case 1): It is the common use to specify a century number as the temporal expressions, like as “8th century”. Since ISO 19108 does not support the reference of the century number, we have defined “Common Century System” class for century orders as a temporal reference system. This class is inherited from the TM_Calendar class. And, to express a specific century number, we have also defined "Common Century" class which is inherited from the TM_coordinate class.
For case 2): It is also the common use to specify Age/Era/Period name as the temporal expressions, like as “Kamakura period (鎌倉時代)”. ISO 19108 defines the ordinal reference system and its element, but it is not fit for the practical use of Age/Era/Period name as the temporal expressions for historical or archaeological objects. We have defined “Chronological Reference System” class to identify the chronological order. This class is inherited from the TM_OrdinalRefenceSystem. And we have defined “Chronological Element” class, that is inherited from the TM_OrdinalEra class, to express each age/era/period names.
Case 3) includes the expressions, e.g., “early stage (前期)”, “the beginning (初頭)”, “the first half (前半)”. This type of qualification defines the part in the range of original period. It is not defined in ISO 19108. We have implemented it by adding “periodical qualifier” attribute in the class definition for the period.
Case 4) includes the expressions, e.g., “from the end of 7th century to the beginning of 8th century (7 世紀末から8 世紀初頭)”, “from the last stage of Nara Period to the beginning of Heian period (奈良時代後期から平安時代初頭)”. We have defined a class that accepts two or more types of the instance including case 3) with optional attribute of the estimated probability.
Case 5) includes the expressions, e.g., “kanoto-i year in Kofun period (古墳時代の辛亥の年)”, “winter in the latter portion of Meiji period (明治時代後葉の冬)”. In these examples, “kanoto-i” is a 48th year in Jikkan (The Ten Stems: 十干) and Junishi (the Twelve Signs of the Chinese Zodiac: 十二支) in the period for 60 years cycle, and “winter” is one of the four seasons in a year cycle. We have added the function expression at the “periodical qualifier” attribute in the class definition of period. The rectangular wave function is a practical case for implementing cyclical temporal expressions. Our approach to enhancing ISO 19108 will be possible to lead the standardization of the temporal expressions for historical or archeological objects on information system. It also will provide the common temporal specification not only for the history or archaeology such as the studies treating the past, but also for the whole field of humanities.
temporal attribute, history, archaeology, chronology