Customised Temporal Encoding Standards Working Group Proposal

The Temporal Domain Working Group have proposed that a standards working group be established to address a particular set of requirements emerging from the domain working group.

This page is the working draft for the project scope and project description for this potential SWG.

1. Customised Temporal Reference Systems Standards Working Group

2. Purpose of this Standards Working Group

The purpose of this standards working group is to adapt a set of existing standards to provide the capability to represent and encode temporal metadata within data sets and protocols which uses a customised calendar.

3. Business Value Proposition

The temporal domain working group has identified a range of communities who use time representations based on calendars which are not the Gregorian calendar as recognised by the International Standards Organisation (in ISO8601).

In order to provide interoperable representations of this metadata, in data payloads and in standards, extensions to the current metadata standardisation provision are required.

This has particular business value for the Climate Science community, who make extensive use of such temporal representations, and for the wide range of OGC communities who are looking to make use of climate data to interact with their own data sets facilitating further applications.

4. Scope of the Work

It is expected that this work will involve adaptions and extensions to existing OGC standards and ISO standards developed in conjunction with the OGC. This will include proposing and managing changes to relevant standards where this is required.

This work programme will deliver:

4.0.1 Formal definitions of calendars and temporal coordinate system.

4.0.2 Encoding of calendar based temporal coordinate reference system instances in ISO 19162 Well Known Text.

4.0.3 Formal definitions of temporal entities (instant, period) with respect to calendars and temporal coordinate systems.

4.1 Relationship to OGC Standards Baseline

4.1.1 Use Cases

4.1.1.1 Encoding a numerical coordinate using a Well Known Text string and a 360 day calendar.

4.1.1.2 Encoding a time period within a 360 day calendar as a parseable, human and machine readable string.

4.1.1.3 Translation between a time period string and a numerical coordinate and CRS for a 365 day calendar.

4.1.1.4 Encoding temporal information in a non-greogrian civil calendar, for example the Hijri Calendar used in Saudi Arabia.

4.1.1.x ...

4.1.2 Current Standards

The ISO standards which influence this domain and may require updating:

• ISO 8601 - Data elements and interchange formats – Information interchange – Representation of dates and times
• ISO 19108 - Geographic information – Temporal schema
• ISO 19111 - Geographic information – Spatial referencing by coordinates
• ISO 19162 - Well Known Text for Coordinate Reference systems
• OGC 13-102r2 Name type specification – Time and index coordinate reference system definitions

4.2 Out of Scope

4.2.1 Conversion between date-times in different calendars is out of scope.

4.3 Specific Contribution of Existing Work as a Starting Point

• The work of the CRS-WKT SWG provides an encoding framework, in ISO19162, linked to other ISO standards, to handle a set of requirements for Gregorian calendar based temporal metadata.
• ISO8601 provides a notation for encoding times with respect to the gregorian calendar.

4.4 Determination of SWG completion

• The SWG work will be complete when the use cases adopted by the SWG Charter are able to be delivered against using adopted standards.

4.5 This is not a persistent SWG

4.6 SWG dissolution

• Following SWG completion, all information is archived, all proposals adopted and the updated standards available for use by the community.

5 Key Capability Deliverables

5.1 Definition of a Calendar

• ISO 19108 provides a framework for defining a calendar from basic building blocks.
• Defining the gregorian calendar, including leap years and leap seconds is hard. This is not required as ISO8601 mandates that all 8601 definitions are with respect to the gregorian calendar.
• Defining a no leap second gregorian calendar will be required, as many software implementations handle standard time this way.
• Simplified geophysical model calendars are easier to define, with regular periodicity and lacking corrections.

5.2 Definition of an Instant in Time

• A syntax for defining an instant in time, with respect to a calendar is required.
• This enables a zero point to be defined and calculations using offsets from that origin to be undertaken.

5.3 Definition of a Customised Temporal Coordinate Reference System

• A temporal coordinate reference system provides the context to comprehend a numerical temporal coordinate.
• It consists of:
  • a calendar definition;
  • a time origin (sometimes the term epoch is used)
  • a unit of measure

5.4 Encoding of a Customised Temporal CRS in Well Known Text

• ISO 19162 provides the Well Known Text syntax for encoding a TCRS.
• It is currently limited to working with the ISO Gregorian calendar
• We need to be able to define a calendar instance:
  • Do we need syntax to explicitly define the calendar instance in WKT?
  • Can we depend only on some system of external referencing?

5.5 Definition of a time period

• A time period shall have a duration, able to be defined in SI units.
• A time period is defined with respect to a well defined calendar.
• A time period may be specified as a bounded quantity between two well defined instants in time:
  • 2015-06-02:21:20:000 | 2015-06-02:21:30:000
• A time period may be defined the entire duration of a well defined temporal quantity:
  • 2012-06
• <controversial> A time period may be defined by the intersection of a set of independent temporal quantities:
  • 1979 | 2010 ; December | February
  • </controversial>
• A partial time period may be defined by either the start or the end, with the other unknown.

6. IPR Policy

This SWG will be RAND-royalty free.

-- MarkH - 22 Apr 2015