ABCD Schema - Task Group on Access to Biological Collection Data

A joint CODATA and TDWG initiative supported by GBIF

DateTime in the ABCD Schema

The representation of date and time information (e.g. gathering date linked to a collection event) within the ABCD schema should fulfil the following requirements:

1. It should be capable of providing date, time, day of the year (Julian day), and unstructured date and time strings.
2. It should be capable of representing date and time spans (periods).
3. It should allow for entering incomplete date and time information such as data taken from partly unreadable herbarium sheet labels.

Requirement 2 excludes time and date specifications that represent a single point in time only (e.g. the date representation in the “ENHSIN Element Set” and the “Darwin Core”).

Following a decision of the editorial committee meeting in Singapore, ABCD version 1.03 represented date and time using the ISO8601 standard. Provided that an additional element for free text (DateText) is present, the standard fulfils all requirements.

However, the full implementation of this standard (allowing data holders to provide any ISO8601 compliant date and time structure) is considered inadequate for a heterogeneous information network because the provider software will not be capable of searching such fields on the basis of standard SQL expressions.

Therefore, version 1.04 of the ABCD schema includes a new representation of date and time, which uses a subset of ISO8601 but restricts the space of valid date and time strings so that they are searchable with standard SQL comparison operators.

The elements ISODateTimeBegin and ISODateTimeEnd are defining a time span using an ISO conform structure defined by a regular expression in the new DateTimeType. Time can only be given when a full date is supplied (ISO definition):

Example for ISODateTimeBegin and ISODateTimeEnd: December 5, 1966 23:55:46

If providers want to make time of the day and Julian day searchable they can use the additional elements TimeOfDayBegin, TimeOfDayEnd, DayNumberBegin, and DayNumberEnd. Finally, a DateText field may be used house unstructured date and time information that does not fit into one of the other fields.

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This page last edited March 06, 2005