Guidelines for using P82a, P82b, P81a, P81b

Detailed question: 

Properties "P81 ongoing throughout" and "P82 at some time within" are defined in the CRM as E61 Time Primitive, i.e., (closed, contiguous) intervals on the natural time dimension in which we live. Since the E61 Time Primitive of the CRM cannot be expressed in RDF directly, in the official RDF implementation of the CIDOC CRM, we define four properties replacing P81 and P82 which express the Time Primitives as xsd:dateTime values.

 

P81 ongoing throughout

Property P81 describes the maximum known temporal extent of an E52 Time-Span, i.e. the extent it is ongoing throughout. It is replaced in this RDF version by the property "P81a_end_of_the_begin" and "P81b_begin_of_the_end", to be used together.

"P81a_end_of_the_begin" should be instantiated as the earliest point in time the user is sure that the respective temporal phenomenon is indeed ongoing. We call it “end_of_the_begin”, because it also constitutes an upper limit to the end of the indeterminacy or fuzziness of the beginning of the described temporal phenomenon.

"P81b_begin_of_the_end" should be instantiated as the latest point in time the user is sure that the respective temporal phenomenon is indeed ongoing. We call it “begin_of_the_end”, because it also constitutes a lower limit to the beginning of the indeterminacy or fuzziness of the end of the described temporal phenomenon.

It is correct to assign the same value to “P81a_end_of_the_begin” and “P81b_begin_of_the_end”, if no other positive knowledge exists. It is also correct not to instantiate P81 for a time span, if there is no evidence that the temporal phenomenon was definitely occurring at a particular time.

If a value for “P81a_end_of_the_begin” is given with a precision less than that of xsd:dateTime (i.e. seconds), such as in days or years, the implementation should “round it up” to the last instant of this time expression, e.g. 1971 = Dec 31 1971 23:59:59. Respectively, for “P81b_begin_of_the_end” the implementation should “round it down”, e.g. 1971 = Jan 1 1971 0:00:00. [to note that this form is explicitly chosen against other potential ways to express imprecision, for the purpose of normalization and calculation. Potentially add that this works for any time interval year, month, day, minute, second etc.]

P82 at sometime within

Property P82 describes the narrowest known outer bounds of the temporal extent of an E52 Time-Span, i.e. the described temporal phenomenon is definitely ongoing “at some time within” this interval. It is replaced in the official RDF version by the properties "P82a_begin_of_the_begin" and "P82b_end_of_the_end", to be used together.

"P82a_begin_of_the_begin" should be instantiated as the latest point in time the user is sure that the respective temporal phenomenon is indeed not yet happening. We call it “begin_of_the_begin”, because it also constitutes a lower limit to the beginning of the indeterminacy or fuzziness of the beginning of the described temporal phenomenon.

"P82b_end_of_the_end" should be instantiated as the earliest point in time the user is sure that the respective temporal phenomenon is indeed no longer ongoing. We call it “end_of_the_end”, because it also constitutes an upper limit to the end of the indeterminacy or fuzziness of the end of the described temporal phenomenon.

It is not correct to assign the same value to “P82a_begin_of_the_begin” and “P82b_end_of_the_end”. If a value for “P82a_begin_of_the_begin” is given with a precision less than that of xsd:dateTime (i.e. seconds), such as in days or years, the implementation should “round it down” to the first instant of this time expression, e.g. 1971 = Jan 1 1971 0:00:00. Respectively, for “P82b_end_of_the_end” the implementation should “round it up”, e.g. 1971 = Dec 31 1971 23:59:59.

It must always hold that “P82a_begin_of_the_begin” is before “P82b_end_of_the_end”, “P81a_end_of_the_begin” and “P81b_begin_of_the_end”.

It must always hold that “P82b_end_of_the_end” is after “P82a_begin_of_the_begin”, “P81a_end_of_the_begin” and “P81b_begin_of_the_end”.

 “P82a_begin_of_the_begin” and “P82b_end_of_the_end” should always be assigned a value for any past phenomenon. The scholarly practice of not giving outer bounds for an event, because they are not known down to a desired precision (e.g. of three years), is not helpful for automated reasoning. In that case, the machine may conclude that a historical event could have happened at the time of the dinosaurs. Therefore any value is better than no value, even if it is relatively far away from the most likely value. It is an error to associate any implicit degree of approximation  with these values. Only for phenomena that may not yet have ended at the time of documentation can the end of the time-span be omitted.

Negative Time Interval for P81

If a respective reasoning is installed, and no evidence exists  about the point in time that the phenomenon was definitely ongoing, one may specify “P81a_end_of_the_begin” as being later than “P81b_begin_of_the_end”, indicating that the indeterminacy of knowledge (not of being) of the begin overlaps with the indeterminacy of knowledge (not of being) of the end [Holmen, Jon; Ore, Christian-Emil Smith.  educing event chronology in a cultural heritage documentation system.  In : Frischer, Bernard, Jane Webb Crawford and David Koller (eds),​Making History Interactive. Computer Applications and Quantitative Methods in Archaeology (CAA). Proceedings of the 37th International Conference. Archaeopress 2010 ISBN 9781407305561].

 

Entities-Properties per Version: 
Reference to Cidoc Version: 
Post date : 
2018-11-23
Authors: 
crm-sig
Type: 
Best Practices