Add source stewardship extension proposal (#6)

Add note about relocated standard structure
Add link to standard YAML file
Add more examples
Add note about relocated standard structure
Address some PR feedback
Fix example 3
Fix cardinality

Signed-off-by: Dave Thaler <dthaler@armidalesoftware.com>

README.md

@@ -14,6 +14,7 @@ Extensions
 The following extensions are proposed for discussion:
 
 * [Source Derivation Extension](source-derivation-extension.md)
+* [Source Stewardship Extension](source-stewardship-extension.md)
 
 All proposed extensions use [documented extension tags](https://gedcom.io/specifications/FamilySearchGEDCOMv7.html#extension-tags).  If they later become incorporated into the FamilySearch GEDCOM standard,
 standard tags will be defined at that time.

source-stewardship-extension.md

@@ -0,0 +1,122 @@
+# Source Stewardship GEDCOM Extension (Proposed)
+
+FHISO's [Citations: Goals and Considerations](https://fhiso.org/TR/citation-goals) lists some things
+that a data model should support, including provenance.  It notes:
+
+> One kind of layering is derivation: a source can be a copy, translation, transcript,
+> abridgement, etc. of another source. The other kind of layering is transition of stewardship:
+> sources can be held by stewards who obtained the source from other stewards. Not all family history
+> citation styles express both kinds of layering, but enough do that both should be modelled.
+
+The proposed Source Stewardship GEDCOM Extension allows recording the
+transition of stewardship of a given source by permitting a date (range)
+per source repository citation.  For example, stewardship of a Family
+Bible can be recorded using a series of source repository citations,
+each with a date.
+
+See also the [`_DATE` YAML file](yaml/_DATE.yaml) for more details.
+
+**Note**: the `_DATE` YAML file is an anomaly here since `_DATE` is a
+[*relocated standard structure*](https://github.com/FamilySearch/GEDCOM/blob/main/specification/gedcom-1-hierarchical-container-format.md#extensions)
+which means it reuses the `g7:DATE` URI, which has its own
+[YAML file](https://github.com/FamilySearch/GEDCOM-registries/blob/main/structure/standard/DATE.yaml) already.
+There is an [issue](https://github.com/FamilySearch/GEDCOM.io/issues/97) tracking
+possible ways to allow automated validation of relocated standard structures,
+such as a wrapper YAML file.  In that light, an example YAML file is provided here that
+may be used to help construct such a proposal.
+
+## GEDCOM Schema
+
+```gedstruct
+n REPO @<XREF:REPO>@                       {1:1}  g7:REPO
+  +1 <<NOTE_STRUCTURE>>                    {0:M}
+  +1 CALN <Special>                        {0:M}  g7:CALN
+     +2 MEDI <Enum>                        {0:1}  g7:MEDI
+        +3 PHRASE <Text>                   {0:1}  g7:PHRASE
+  +1 _DATE <DateValue>                     {0:1}  g7:DATE
+     +1 TIME <Time>                        {0:1}  g7:TIME
+     +1 PHRASE <Text>                      {0:1}  g7:PHRASE
+```
+
+### `_DATE` (DATE)  `g7:DATE`
+
+The date or date range when a source was held by a specific repository.
+
+### Example 1
+
+The following example is taken from the "Private Holdings: Family Bible
+Records" QuickCheck Model on page 107 of "Evidence Explained", which has a first
+(full) reference note of:
+
+1. John Lynde Greene Sr. Family Bible Records, 1807-1944, *The Holy
+   Bible* (Philadelphia: Matthew Carey, 1811), "Marriages"; privately
+   held by John Lynde Greene IV, Germantown, Maryland, 2001.
+
+This example just has a year when the private holding was known to be
+in the stated repository.
+
+```
+0 @I1@ INDI
+1 SOUR @S1@
+2 PAGE Marriages
+0 @S1@ SOUR
+1 AUTH John Lynde Greene Sr. Family Bible Records, 1807-1944
+1 TITL The Holy Bible
+1 PUBL Philadelphia: Matthew Carey, 1811
+1 REPO @R1@
+2 _DATE 2001
+0 @R1@ REPO
+1 NAME John Lynde Greene IV
+2 ADDR Germantown, Maryland
+3 CITY Germantown
+4 STAE Maryland
+
+```
+
+### Example 2
+
+The following example gives the stewardship of a Family Bible
+that was passed between private holders over time.
+
+```
+0 @S1@ SOUR
+1 TITL Adam Smith Family Bible
+1 REPO @R1@
+2 _DATE TO 1950
+1 REPO @R2@
+2 _DATE FROM 1950
+0 @R1@ REPO
+1 NAME Adam Smith
+0 @R2@ REPO
+1 NAME John Smith
+```
+
+### Example 3
+
+The following example is taken from the "Journal Articles: Online Archives of Print
+Journals" QuickCheck Model on page 780 of "Evidence Explained", which has a first
+(full) reference note of:
+
+1. Deborah A. Rosen, "Women and Property across Colonial America: A Comparison of Legal
+Systems in New Mexico and New York," *The William and Mary Quarterly* 91 (April 2003); online archives,
+*The History Cooperative* (http://www.historycooperative.org/journals/wm/60.2/rosen.html :
+accessed 25 April 2007), para. 21.
+
+This example has an "accessed" date when the information was known to be
+on a given website.
+
+```
+0 @I1@ INDI
+1 SOUR @S1@
+2 PAGE para. 21.
+0 @S1@ SOUR
+1 AUTH Deborah A. Rosen
+1 TITL "Women and Property across Colonial America: A Comparison of Legal Systems in New Mexico and New York"
+1 PUBL The William and Mary Quarterly 91 (April 2003)
+1 REPO @R1@
+2 CALN http://www.historycooperative.org/journals/wm/60.2/rosen.html
+2 _DATE 25 APR 2007
+0 @R1@ REPO
+1 NAME The History Cooperative
+1 WWW http://www.historycooperative.org
+```

yaml/_DATE

@@ -0,0 +1,37 @@
+%YAML 1.2
+---
+lang: en-US
+
+type: structure
+
+uri: https://github.com/dthaler/gedcom-citations/_DATE
+
+extension tags:
+  - _DATE
+
+specification:
+  - Date
+  - |
+    The principal date of the subject of the superstructure. The payload is a
+    DateValue.
+
+    See DATE_VALUE for more.
+  - |
+    A date, optionally with a time and/or a phrase. If there is a TIME, it
+    asserts that the event happened at a specific time on a single day. TIME
+    should not be used with DatePeriod but may be used with other date types.
+
+    There is currently no provision for approximate times or time phrases. Time
+    phrases are expected to be added in version 7.1.
+
+label: 'Date'
+
+payload: https://gedcom.io/terms/v7/type-Date
+
+substructures:
+  "https://gedcom.io/terms/v7/PHRASE": "{0:1}"
+  "https://gedcom.io/terms/v7/TIME": "{0:1}"
+
+superstructures:
+  "https://gedcom.io/terms/v7/REPO": "{0:M}"
+...