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DCMI Period Encoding Scheme

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: 2005-07-25
Is Replaced By:
Latest version:
Status of document: This is a DCMI Proposed Recommendation. From 2005-07-25 to 2005-10-10, the status of this revision was incorrectly shown as "DCMI Recommendation"..
Description of document: This document defines ‘DCMI Period’, a mechanism for indicating a single time interval using its limits. Components of the value correspond to the start and end of the interval, either of which may be omitted in the case of a single-ended interval. We describe a method for encoding DCMI Period in a text-string, as a profile of DCSV. This notation is intended for recording the value of the DCMES elements Coverage and Date.

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 scheme from which it is selected determines its meaning.

  1. 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 profile of DCSV [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 Definition Default1
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 -

1*All components are optional._
*2 If 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.
3 If 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.
4 In 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. Thus, use of DCMI Period to identify a time interval requires that the components are linked together. 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 [DCSV] recommendation.

3.1 DCSV encoding

Writing DCMI Period using DCSV notation is straightforward, using the component names defined above. A DCMI Period value appears as follows:

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

where v1 - v4 are 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

S. Cox, 2000, DCMI Box - specification of the spatial limits of a place, and methods for encoding this in a text string

1999. Dublin Core Metadata Element Set, Version 1.1: Reference Description

Dublin Core Metadata Initiative, OCLC, Dublin Ohio.

S. Cox, R. Iannella, 2000. A syntax for writing a list of labelled values in a text string

Mathematical Markup Language (MathML) 1.01 Specification

M. Wolf, C. Wicksteed, 1997, Date and Time Formats

Extensible Markup Language