Initial strawman of EXID-TYPE registry.

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

README.md

@@ -11,6 +11,7 @@ If you are looking for FamilySearch's GEDCOM 5.5.1 Java parser, which previously
 ## Repository structure
 
 - [`changelog.md`](changelog.md) is a running log of major changes made to the specification.
+- [`exid-types.json`](exid-types.json) is a JSON file containing registered EXID-TYPE values.
 - [`specification/`](specification/) contains the FamilySearch GEDCOM specification:
 	- `specification/gedcom-`number`-`title`.md` files are the source documents used to define the FamilySearch GEDCOM specification. It is written in pandoc-flavor markdown and is intended to be more easily written than read. It is splint into several files (ordered by the integer in their names) to facilitate comparing files.
 	- In a local check-out, this is also where the build scripts place rendered files `gedcom.html` and `gedcom.pdf`; see [releases](releases/latest) for a pre-rendered copy of these.

exid-types.json

@@ -0,0 +1,28 @@
+[
+  {
+    "label": "AFN",
+    "type": "https://gedcom.io/terms/v7/AFN",
+    "description": "Ancestral File Number",
+    "contact": "GEDCOM@familysearch.org",
+    "change-controller": "FamilySearch",
+    "reference": "https://gedcom.io/migrate/#afn-rfn-rin"
+  },
+  {
+    "label": "RIN",
+    "type": "https://gedcom.io/terms/v7/RIN",
+    "description": "Automated Record ID",
+    "contact": "GEDCOM@familysearch.org",
+    "change-controller": "FamilySearch",
+    "fragment": "Source System",
+    "reference": "https://gedcom.io/migrate/#afn-rfn-rin"
+  },
+  {
+    "label": "RFN",
+    "type": "https://gedcom.io/terms/v7/RFN",
+    "description": "Permanent Record ID",
+    "contact": "GEDCOM@familysearch.org",
+    "change-controller": "FamilySearch",
+    "fragment": "Resource ID",
+    "reference": "https://gedcom.io/migrate/#afn-rfn-rin"
+  }
+]

specification/gedcom-03-datamodel.md

@@ -1703,6 +1703,8 @@ the authority owning the identifier is provided in the TYPE substructure; see `E
 
 Depending on the maintaining authority, an `EXID` may be a unique identifier for the subject, an identifier for 1 of several views of the subject, or an identifier for the externally-maintained copy of the same information as is contained in this structure. However, unlike `UID` and `REFN`, `EXID` does not identify a structure; structures with the same `EXID` may have originated independently rather than by edits from the same starting point.
 
+`EXID` identifiers are expected to be unique and durable.
+
 #### `FAM` (Family record) `g7:record-FAM`
 
 See `FAMILY_RECORD`
@@ -2713,6 +2715,18 @@ If the authority maintains stable URLs for each identifier it issues,
 it is recommended that the `TYPE` payload be selected such that appending the `EXID` payload to it yields that URL.
 However, this is not required and a different URI for the set of issued identifiers may be used instead.
 
+Registered URIs are listed in [exid-types.json](https://github.com/FamilySearch/GEDCOM/blob/main/exid-types.json), where fields include:
+* "label": a short string suitable for display in a user interface.
+* "type": The URI representing the authority issuing the `EXID`.
+* "description": A description of the meaning of the `EXID`.
+* "contact": A contact email address for the person or organization registering the URI.
+* "change-controller": The name or contact information for the person or organization authorized to update the registration.
+* "fragment": If present, indicates a short string that can be used as a label for a fragment identifier appended to the URI.  If absent, indicates that fragment identifiers are not used with the URI.
+* "reference": A URL with more information about the meaning of the `EXID`. Such information should explain the uniqueness and expected durability of the identifier.
+
+Additional type URIs can be registered by filing a
+[GitHub pull request](https://github.com/FamilySearch/GEDCOM/pulls).
+
 #### `UID` (Unique Identifier) `g7:UID`
 
 A globally-unique identifier of the superstructure,