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CLDR Ticket #10651(new)

Opened 16 months ago

Last modified 7 weeks ago

Review and clarify the criteria for metazone

Reported by: yoshito Owned by: yoshito
Component: timezone Data Locale:
Phase: dsub Review:
Weeks: Data Xpath:
Xref:

ticket:10060

Description

When we introduced the concept of meta zone, we had to introduce a concept - "golden zone". A golden zone for a metazone is used when parsing a display name coming from the metazone, because a metazone might be mapped from multiple zones. When parsing display name back to a zone, we need to pick one.

There are two types of metazones.

The First type is metazones not associated with any specific locations. For example, "America_Eastern", "Europe_Central", "Afrika_Western".. are included in this category. For these zones, we need to pick one zone that can be mapped to the metazone all the time since 1970. Then, if there are other zones that satisfy the criteria, these zones can be regional golden zones. Usually, such golden zones uses the same standard UTC offset and same daylight saving time offset since 1970 (For example, America_Eastern - standard time is UTC-5 / daylight time is UTC-4).

The second type is metazones associated with specific locations. For example, metazone "China", "Chile", "Goose_Bay" etc.. fall into this category. The criteria for the golden zones for these zones is still if such zone can be mapped to the metazone all the time since 1970. But unlike the first type, such metazones are usually tied to single country or region (may have some related zones which are historically used slightly different rule), and display names for these region usually use location name. UTC offset may change time to time.

For the second type, we might be able to retire many of them because location based name composed from zone's location would suffice most of cases. Even some of them really mapped from/to multiple (related) zones, it's usually not so difficult to maintain mappings.

The problem is the first type. The criteria of golden zone is based on zone mapping starting 1970-01-01. For me, historic year range is too long and it introduced a strange issue. For example, metazone GMT. You would imaging Europe/London would be the reference (golden) zone, but I'm not sure it really satisfy the criteria of golden zone, because London stayed in BST for a few years around 1970.

...
# Summer Time Order, 1961 (S.I. 1961/71)
# Summer Time (1962) Order, 1961 (S.I. 1961/2465)
# Summer Time Order, 1963 (S.I. 1963/81)
Rule	GB-Eire	1961	1963	-	Mar	lastSun	2:00s	1:00	BST
Rule	GB-Eire	1961	1968	-	Oct	Sun>=23	2:00s	0	GMT
# Summer Time (1964) Order, 1963 (S.I. 1963/2101)
# Summer Time Order, 1964 (S.I. 1964/1201)
# Summer Time Order, 1967 (S.I. 1967/1148)
Rule	GB-Eire	1964	1967	-	Mar	Sun>=19	2:00s	1:00	BST
# Summer Time Order, 1968 (S.I. 1968/117)
Rule	GB-Eire	1968	only	-	Feb	18	2:00s	1:00	BST
# The British Standard Time Act, 1968
#	(no summer time)
# The Summer Time Act, 1972
Rule	GB-Eire	1972	1980	-	Mar	Sun>=16	2:00s	1:00	BST
Rule	GB-Eire	1972	1980	-	Oct	Sun>=23	2:00s	0	GMT
# Summer Time Order, 1980 (S.I. 1980/1089)
# Summer Time Order, 1982 (S.I. 1982/1673)
# Summer Time Order, 1986 (S.I. 1986/223)
# Summer Time Order, 1988 (S.I. 1988/931)
Rule	GB-Eire	1981	1995	-	Mar	lastSun	1:00u	1:00	BST
Rule	GB-Eire 1981	1989	-	Oct	Sun>=23	1:00u	0	GMT
# Summer Time Order, 1989 (S.I. 1989/985)
# Summer Time Order, 1992 (S.I. 1992/1729)
# Summer Time Order 1994 (S.I. 1994/2798)
Rule	GB-Eire 1990	1995	-	Oct	Sun>=22	1:00u	0	GMT
# Summer Time Order 1997 (S.I. 1997/2982)
# See EU for rules starting in 1996.
#
# Use Europe/London for Jersey, Guernsey, and the Isle of Man.

# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
Zone	Europe/London	-0:01:15 -	LMT	1847 Dec  1  0:00s
			 0:00	GB-Eire	%s	1968 Oct 27
			 1:00	-	BST	1971 Oct 31  2:00u
			 0:00	GB-Eire	%s	1996
			 0:00	EU	GMT/BST

In some cases, we might encounter a situation that there are no golden zone for a metazone by the current definition.

I propose to review the real goals of metazones, whether we need golden zones, if so, what is exact criteria. I personally feel changing the start point of metazone from 1970-01-01 to more recent date (e.g. 2000-01-01) may greatly reduce the complexity of mapping, and make golden zones more "reasonable" matching ordinary people's expectation.

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Change History

comment:1 Changed 11 months ago by yoshito

  • Xref set to 10060

comment:2 Changed 2 months ago by mark

  • Milestone changed from UNSCH to to-assess

comment:3 Changed 7 weeks ago by mark

  • Owner changed from anybody to yoshito
  • Component changed from unknown to timezone
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