add established_date to entity

documentation/properties/established_date.md

@@ -0,0 +1,22 @@
+layout:		property
+title:		"established_date"
+schemas:	[customer, issuer, guarantor]
+---
+
+# established_date
+
+---
+
+The **established_date** reflects the date from which the investee’s business age is determined. This may differ from the legal incorporation date.
+
+For PRA-regulated entities, this field supports compliance with Article 133 of the CRR as implemented under Basel 3.1, including the assessment of how long a business has existed for equity exposure risk-weight determination.
+
+In accordance with the PRA definition, **established_date** is the date from which the business age begins to be calculated, and should reflect:
+1. where the business was first established within the current undertaking, the date the business was first established within that undertaking; or
+2. where the business was established within a different undertaking and subsequently transferred:
+        - the original establishment date if the risk profile and nature of the business did not substantially change as a result of the transfer; or
+        - the date of transfer if the risk profile or nature of the business substantially changed as a result of the transfer.
+
+For additional details refer to: https://www.prarulebook.co.uk/
+
+---

schemas/entity.json

@@ -133,6 +133,11 @@
         "d"
       ]
     },
+    "established_date": {
+      "description": "The effective date from which the investee’s business age is determined. Formatted as YYYY-MM-DDTHH:MM:SSZ in accordance with ISO 8601.",
+      "type": "string",
+      "format": "date-time"
+    },
     "fitch_lt": {
       "description": "Fitch long term credit ratings",
       "type": "string",