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Table 4 Part of the archaeological periodization (based on Onroerend Erfgoed 2012 ) used in the
temporal ordinal reference system assessment
Roman time
57 BC
Middle ages
New time
a minimal begin and maximal end value for this temporal category or use a date
range. Based on these elements, different probability calculations can be per-
formed analogous to Green ( 2011 ). The absolute time of the complete site refers
to the period of occupation or use and can, accordingly, be represented by a TM_
Period. The remarks concerning the dating imperfection remain valid here as well.
5.2 Temporal Ordinal Reference System
For the archaeological time the temporal position is specified relative to a tem-
poral ordinal reference system, namely the archaeological time scale. To clarify
the differences between the ISO 19108 structure and structures adapted for the
geological time scale (Cox and Richard 2005 ; Michalak 2005 ), only a part of
the archaeological time scale is used (Table 4 ). The begin and end dates used in
Table 4 are not fixed, but are rough estimations described by the Flemish Heritage
Agency (Onroerend Erfgoed 2012 ).
The structure of a temporal ordinal reference system described in the
NBN EN ISO 19108:2005 standard (NBN 2005 ) is shown in Fig. 5 . The class
TM_OrdinalReferenceSystem is a subclass of TM_ReferenceSystem which holds
two attributes: 'name' and 'domainOfValidity'. The latter attribute allows defining
a time span in which the reference system is valid, or a spatial extent for which the
reference system can be used, or a combination of both (NBN 2005 , p. 17).
Figure 9 presents the part of the archaeological time scale given in Table 4 in
conformity with the NBN EN ISO 19108 standard. It can immediately be noticed
that the same dates are reoccurring. For instance the end time of the Roman
time period, 476 AD, appears at three different places in the model (Fig. 9 ). This
implies redundancy, which has to be avoided in data modelling to minimize the
chance of inconsistency. The model also indicates clearly the begin and end dates
of each of the (sub)periods. Although these dates are roughly known, they do not
represent precise boundaries of the periods. This remark is also made by Cox and
Richard ( 2005 , p. 122): “[…] the limits of TM_OrdinalEra are defined precisely
by attributes of type DateTime. However, in historic, archaeological contexts,
and certainly in the geological time scale, while the order of eras within a TORS
[Temporal Ordinal Reference System] is known, the positions of the boundaries
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