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DCMI Period Encoding Scheme: specification of the limits of a time interval, and methods for encoding this in a text string

Creator: Simon Cox
Contributor: Andy Powell
Contributor: Andrew Wilson
Date Issued: 2006-04-10
Identifier: http://dublincore.org/documents/2006/04/10/dcmi-period/
Replaces: http://dublincore.org/documents/2000/07/28/dcmi-period/
Is Replaced By: Not Applicable
Latest version: http://dublincore.org/documents/dcmi-period/
Status of document: This is a DCMI Recommendation.
Description of document: This document defines DCMI Period, a mechanism for indicating a single time interval using its limits and representing that information as a text string. Components of the value string correspond to the start and end of the interval, either of which may be omitted in the case of a single-ended interval. A method for encoding DCMI Period in a text string using the DCSV syntax is described. This notation is intended for representing a value of the DCMES elements Coverage and Date.
Revision note: 2006-04-10. After approval of the DCMI Abstract Model [DCAM] as a DCMI Recommendation in March 2005, the DCMI Usage Board undertook a review of the DCSV syntax specification and of the related specifications for the encoding schemes DCMI Box, DCMI Point, and DCMI Period, with the goal of revising their language for conformance with the Abstract Model. A summary of the changes made can be found in the document "Revision of DCSV specifications". As of 2005, the DCMI Abstract Model supports the construct "related description" as a method for describing value entities such as a persons or, indeed, time periods or locations in space. The DCMI Usage Board encourages implementers to consider using related descriptions as an alternative to packaging descriptive information in DCSV-encoded strings. Descriptions based on the DCMI Abstract Model are more likely to be interoperable over the longer term than descriptions using DCSV-syntax-based specifications.

Table of Contents

1. Introduction

Several methods are available to indicate a time interval. These include, but are not limited to:

The Dublin Core Metadata Element Set [DCMES] includes two elements, Coverage and Date, the values of which may indicate a time interval.

If a name is used then the enumeration from which it is selected determines its meaning.

The W3C profile of the ISO8601 standard for dates and times [W3C-DTF] is generally useful for identifying time instants but does not provide an explicit mechanism for indicating a time interval.

This document defines DCMI Period, an encoding scheme which uses a simple model to specify the limits of a time interval, and describes a method for encoding DCMI Period as a text string using the DCSV syntax [DCSV]. DCMI Period has been designed to be similar to DCMI Box [BOX] used for identifying a place, and thus allows consistent encoding of spatio-temporal information in the DCMES element Coverage, as well as consistency between Coverage and Date. The components of DCMI Period re-use the W3C-DTF syntax where possible.

DCMI Period indicates a single time interval. If an indication of a time instant is required, then W3C-DTF [W3C-DTF] is available. For multiple disjoint intervals, repeated instances of DCMI Period may be used. DCMI Period is unsuited for identification of recurring and periodic time intervals.

2. Identifying a time interval - the DCMI Period encoding scheme

The time interval is indicated by specifying the start and end of the interval.

We define the following components to describe the interval:

Component Label Definition Default Component Value1
start The instant corresponding to the commencement of the time interval -INF2
end The instant corresponding to the termination of the time interval INF2
scheme The encoding used for the representation of the time-instants in the start and end components3 W3C-DTF
name A name for the time interval4 -

1All components are optional.
2If either start or end is absent, then this implies an interval unbounded on that side. Thus, a DCMI Period with a single component start="2000-01-26" would identify the interval starting at the beginning of Australia Day in the year 2000 C.E. and continuing from that time.
3If a non-numeric encoding is used then matching is maximally inclusive: i.e. if a start component is expressed as a named era then the interval being identified starts at the beginning of the era, and conversely for an end component the interval ends at the end of the named era.
4In this context the name is non-normative. In the case of a conflict, the interval identified by the start and end values takes precedence. The name is provided for user convenience only.

3. Encoding DCMI Period

The components of a DCMI Period identifier have no meaning when disaggregated, since in any particular instance it is the complete set which indicates the specific time interval. For systems in which data is encoded using a limited character set, this is conveniently accomplished by packaging the components into a single text string according to the DCSV recommendation [DCSV] .

A DCMI Period value string using DCSV syntax, and using the component names defined above, appears as follows:

start=v1; end=v2; scheme=v3; name=v4;

where v1 - v4 are component values as defined in the table above.

All components are optional but must not be repeated. The ordering is not significant.

4. Examples

The Great Depression:

name=The Great Depression; start=1929; end=1939;

Perth International Arts Festival, 2000:

name=Perth International Arts Festival, 2000; start=2000-01-26; end=2000-02-20;

1999 AFL Grand Final [AFL is an obscure Australian ball game]:

start=1999-09-25T14:20+10:00; end=1999-09-25T16:40+10:00; scheme=W3C-DTF;

The Phanerozoic Eon:

start=Cambrian period; scheme=Geological timescale; name=Phanerozoic Eon;

5. References

[BOX]
S. Cox, 2000, DCMI Box - specification of the spatial limits of a place, and methods for encoding this in a text string
http://dublincore.org/documents/dcmi-box/

[DCMES]
1999. Dublin Core Metadata Element Set, Version 1.1: Reference Description
http://dublincore.org/documents/dces/

[DCSV]
S. Cox, R. Iannella, 2000. A syntax for writing a list of labelled values in a text string
http://dublincore.org/documents/dcmi-dcsv/

[W3C-DTF]
M. Wolf, C. Wicksteed, 1997, Date and Time Formats
http://www.w3.org/TR/NOTE-datetime

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