Domain Cross References

A data domain (domain) can cross-reference another in its definition creating a relationship between two or more domains. In the following diagram, the student domain makes a cross-reference to the country domain:

When a student MDR is POSTed, the request body would include a reference to a specific country master data record:

{
	"studentID": "XYZ-123",
	"name": "Juana Masa",
	"homeCountry": "/mdrs/country:v1/MEX",
	"birthday": "946684800"
}

When the student MDR is referenced (i.e. GET)  the response will insert the appropriate country information:

{
	"studentID": "XYZ-123",
	"name": "Juana Masa",
	"homeCountry": {
		"name": "Mexico",
		"abbreviation": "MEX",
		"capitalCity": "Mexico City"
	},
	"birthday": "946684800"
}

The cross-reference can be to an entire master data record (e.g. all of the properties for Mexico in the MDR):

    "homeCountry": "/mdrs/country:v1/MEX",

Or for a specific property in the master data record (e.g. just the country name):

    "homeCountry": "/mdrs/country:v1/MEX/name",

Defining a Cross-Reference in the modelSchema

To reference another domain, include the cross-reference property definitions "type": "uri",   "uriType": "xref"  and "xrefLocation". The xrefLocation is the  MDR path to another  MDR or a property of the another MDR.  

{
	"modelSchema": {
		"properties": {
			"<property1>": {
				"type": "uri",
				"uriType": "xref",
				"xrefLocation": "<path (or UUID) of a domain or domain property>",
				""
				...other item1 properties....
			},
			"<property2>": {
				 ... 
			}
		}
	}
}

xrefLocation

When defining a reference, the  domain path to the reference is used.  When POSTing data for the reference the MDR path is used. Some examples will help clarify:

Reference an Entire Master Data Record

When POSTing the reference, the xrefLocation entry in the model schema for referencing a complete MDR would be:

   "xrefLocation": "/domains/{domain-name}[:v<version>]"

e.g.

"homeCountry": {
	"type": "uri",
	"uriType": "xref",
	"xrefLocation": "/domains/country:v1"
}

When POSTing the data for the reference use the displayName of the desired MDR e.g.:

"homeCountry": "/mdr/country:1/MEX"

Reference a Property in a Master Data Record

    "xrefLocation": "/domains/{domain-name}[:version][/property]"

e.g.

"homeCountry": {
	"type": "uri",
	"uriType": "xref",
	"xrefLocation": "/domains/country:v1/name"
}

An Example

The following demonstrates in more detail the example where properties from an existing country domain is to be referenced by a new domain called students.  Assume the country domain contains many properties including the country name and the address for the immigration office. The student domain will reference the countries domain twice:

1. In a property called homeCountry 
2. A property called immigrationAddress

GET the address Property in the countries Model Schema

GET /domains/country/properties?version=1

[
	{
			.
			.
		"propertyName": "immigrationAddress",
		"propertyType": "node",
				.
			.
	},
	{
			.
			.
		"propertyName": "name",
		"propertyType": "string"
			.
			.
	}
]

Create a New students Domain and Add the Cross-Reference To the First Version's Model Schema

POST /domains/versions/<students-domain-uuid>

{
	"modelSchema": {
		"properties": {
			"homeCountry": {
				"type": "uri",
				"uriType": "xref",
				"xrefLocation": "/domains/country:v1/name"
			},
			"immigrationAddress": {
				"type": "uri",
				"uriType": "xref",
				"xrefLocation": "/domains/country:v1/immigrationAddress"
			},
			    .
		        .
                .
		}
	}
}

Note that homeCountry is a primitive type while immigrationAddress is a node and  contains several items such as street, city, province-state, postal-code.

Again, the students domain could just reference the country MDR once which would cause the entire country MDR to be inserted.

How to Establish Circular Cross-References

Consider the situation where a state domain needs to reference to country and country needs a reference back to multiple state MDRs.

This creates a "chicken-or-the-egg" problem since the schema for one will exist before the other. To remedy one of the domains can be updated after both are created. For example:

1. POST the modelSchema for the state domain:

"name": {
	"type": "string"
}

2. POST the domain for country with a model schema that includes a reference to state including the xrefLocation:

"name": {
	"type": "string"
},
"state": {
	"type": "uri",
	"uriType":"xref",
	"xrefLocation": "/domain/state:v1/name" 
}

3. PATCH the domain for state with a model schema that includes the reference to country:

"name": {
	"type": "string"
},
"country": {
	"type": "uri",
	"uriType": "xref",
	"xrefLocation": "/domain/country:v1/name"
}

Data can be posted only if all uri's of type xref have valid xrefLocation`s.

PATCHing a domain:version is denied if any data is POSTed to it.