The "Date" data type provides support for expressing individual points in time. The precision with which the time point may be specified varies from year-level to the level of a second. Dates are given and displayed in the ISO-standard format, i.e. YYYY-MM-DD hh:mm:ss (YYYY = year in the range 0000-9999, MM = arithmetic month of the Gregorian calendar in the range 1-12, DD = day within the month in the range 1-31, hh = hour in the range 0-23, mm = minute in the range 0-59 and ss = second in the range 0-59). The following examples illustrate acceptable values for a date slot:

1. 2006
2. 2006-03
3. 2006-03-25
4. 2006-03-25 10
5. 2006-03-25 10:58
6. 2006-03-25 10:58:43

The precision used to denote the time quantity will be termed as granularity in this document. Note that the year is mandatory. Two more values are acceptable as dates, more specifically the strings unknown and now. The unknown value can be used to signify that the date is not known, while the now value should be interpreted as always being equal to the current "wall clock" indication.

The "Period" data type provides support for expressing anchored segments of the time axis, i.e. time intervals with a specific beginning and a specific end. A period is entered as a pair of dates, enclosed in square brackets ([]) and separated with a comma. The dates may be expressed in different granularities, but it is required that the starting date should be less or equal to the end date. The following examples illustrate acceptable values for a period slot:

• [2002, 2006]
• [2002-01, 2002-01]
• [2002-01-18 10:32:11, 2006-03-25 10:58:43]
• [2002-01-18 10:32:11, 2006-03]

Contrary, the following examples illustrate unacceptable values for a period slot:

• [2006-03-25, 2002-01-18] (ending date is before the starting date)
• [2006, 2006-10-01] (starting date represents the whole of the year 2006, which includes dates that are after the ending date).

Semantically, a period is considered to include both the starting and the ending time point, e.g. the period [2002-01, 2002-02-12] is considered to include the whole of January 2002 and the twelve first dates of February. This is particularly important for the notion of overlapping periods used in the context of non-multiple temporal types (discussed in the next paragraphs). According to the adopted semantics, periods [2002-01, 2002-02-12] and [2002-02-12, 2002-03] do overlap (since they both include February 12, 2002), while periods [2002-01, 2002-02-12] and [2002-02-13, 2002-03] do not overlap.

The special date values unknown and now may be used for the starting or the ending date of a period (or both). In such a case, no check is performed that the starting date should be before the ending date.

The "t-String" data type allows for entering string-typed values that retain their evolution through time. For example, consider the case that we want to retain history of the addresses at which some organization is installed; for this purpose we would use a t-String typed slot named "Address". In the instance editing window, the slot would be rendered as standard Protégé list box, and we would use the "Add Value" button to enter the proper values for the organization whereabouts, each one tagged with a period expressing when the organization was installed at the specific location, e.g.:

[2000-01-30, 2004-12-06]	Somewhere, Someplace 23, 12345, Neverland
[2004-12-07, 2006-03-08]	Elsewhere, Otherplace 42, 34567, Neverland
[2006-04, now]	Anywhere, Anyplace 4, 67890, Neverland

Note that it is allowed to use mixed granularities across periods timestamping different values (i.e. the first two rows use day-level granularity, while the third one employs month-level); the use of "now" and "unknown" is also permitted.

The semantics for the "multiple" check box in the slot property window are modified for the t-String data type as follows:

1. if the "multiple" check box is not checked, then it is not allowed for any two list entries to have overlapping timestamps i.e. not multiple means that for any given point in time, at most one value is allowed. If entries with overlapping timestamps are detected in the list, the slot value is considered erroneous and the list is highlighted with a red border, while the tooltip text is set to indicate the offending periods.
2. if the "multiple" check box is checked, then the timestamp overlap check is not performed, effectively allowing any number of list entries to have overlapping timestamps. This may be used to model cases that multiple values for a single point in time are allowed in the real world, such as organizations with multiple installations (e.g. headquarters, agencies, warehouses etc), lists of professors serving in a University department and so forth.

Under these definitions, the value list depicted in the following table is not valid for a t-String slot characterized as "non-multiple" because the second and third rows have overlapping timestamps; the same value list is valid for a t-String slot characterized as "multiple".

[2000-01-30, 2004-12-06]	Somewhere, Someplace 23, 12345, Neverland
[2004-12-07, 2006-03-08]	Elsewhere, Otherplace 42, 34567, Neverland
[2005-11, 2006-04-18 10:11]	Wherever, Everyplace 88, 98765, Neverland
[2006-04, now]	Anywhere, Anyplace 4, 67890, Neverland

No overlap check is performed for timestamps using the "now" and "unknown" date representations at either end.

These data types are similar regarding the semantics and operation with the t-String data type, differing only in the type of the data that may be entered. Booleans, in particular, can be entered as "true" or "false", while instances can be picked from the standard Protégé "Select Instance" window.