IdAS XDI Mapping

{{#eclipseproject:technology.higgins}} This page documents the mapping between the Higgins Data Model (which is implemented by IdAS) and XDI. XDI ("XRI Data Interchange") is a data model and protocol for sharing, linking, and synchronizing data over the Internet ("structured web") and other networks using Extensible Resource Identifiers (XRIs). It is being developed by the OASIS XDI Technical Committee.

The IdAS XDI Engine exposes an IdAS Context by receiving XDI messages.

The XDI Context Provider implements an IdAS Context by sending XDI messages. These message can be sent either to an XDI endpoint exposed by the IdAS XDI Engine or to a native XDI endpoint.

Mapping the Higgins Data Model to XDI

Since the Higgins Data Model is based on RDF/OWL, and since XDI is also (conceptually) based on RDF, the basic mapping is straight-forward. However, some attention has to be paid to details.

Roughly speaking, a Higgins context can be mapped to an XDI graph using the following rules:

• An Entity maps to an XDI subject
• An Attribute maps to an XDI predicate
• A Simple Value of an Attribute maps to an XDI inner graph with multiple XDI literals
• A Complex Value maps to an XDI reference
• A Higgins Relation maps to an XDI predicate
• A Higgins Correlation maps to the special $is XDI predicate

Hash I-Numbers

On several occasions in this mapping, it is necessary to refer to individual Simple Values of a multi-valued Attribute. Since Simple Values in Higgins IdAS do not have persistent identifiers, a mechanism called "Hash I-Number" (HIN) is used. A HIN is an i-number that is deterministically calculated from a value, therefore acting as an index of that value in the multi-valued Attribute.

This formula can be used to calculate a HIN:

HIN = '$' + '!' + sha1(value)

Examples:

• "Sergey" becomes $!11cac773045ffc189fa2e3ed232843d363d019c6
• "Markus" becomes $!da649486d19f8cc02350447179637cba604eff46
• "markus.sabadello@gmail.com" becomes $!546de0b559ddcdb45983fd901f8d665ecc795e6e
• "msabadello@parityinc.net" becomes $!710e4214a22c1840fc7a829b1c3fd32375e9efca
• "markus@changedemail.com" $!6ea54708b267b24988beca6adc34c4e79ed0a0b5
• "markus@newemail.com" becomes $!83d3033bdaf1ad79b805cbf56df1d5c56c36d71e

Mapping Higgins IdAS operation to XDI operations

Using IdAS, a Higgins context can be opened, and operations can be performed on it. The equivalent in XDI is XDI messages (which contain XDI operations).

All XDI examples are in the X3 Simple serialization format. See X3Format for more information about X3 serialization formats.

List all Entities in the Context

IdAS calls:

Iterator<Entity> entities = context.getEntities(null);

Message sent by the XDI Context Provider to <url>:

=sender
	$get

HTTP REST:

GET on <url>

Reply from the XDI endpoint:

=markus	<-- one entity in the context -->
	+(http://www.example.com/name)
		/
			$!da649486d19f8cc02350447179637cba604eff46
				+(http://www.example.com/name)
					"Markus"
	+(http://www.example.com/location)
		/
			$!8b6cea61d247482e9e7f1e7efb1db432a69bbcb2
				+(http://www.example.com/location)
					"Vienna"
	+(http://www.example.com/email)
		/
			$!546de0b559ddcdb45983fd901f8d665ecc795e6e
				+(http://www.example.com/email)
					"markus.sabadello@gmail.com"
			$!710e4214a22c1840fc7a829b1c3fd32375e9efca
				+(http://www.example.com/email)
					"msabadello@parityinc.net"
=sergey	<-- another entity in the context -->
	+(http://www.example.com/name)
		/
			$!11cac773045ffc189fa2e3ed232843d363d019c6
				+(http://www.example.com/name)
					"Sergey"

Get one Entity from the Context

IdAS calls:

IEntity entity = context.getEntity("=markus");

Message sent by the XDI Context Provider to <url>:

=sender
	$get
		/
			=markus

HTTP REST:

GET on <url>/=markus

Reply from the XDI endpoint:

=markus
	+(http://www.example.com/name)
		/
			$!da649486d19f8cc02350447179637cba604eff46
				+(http://www.example.com/name)
					"Markus"
	+(http://www.example.com/location)
		/
			$!8b6cea61d247482e9e7f1e7efb1db432a69bbcb2
				+(http://www.example.com/location)
					"Vienna"
	+(http://www.example.com/email)
		/
			$!546de0b559ddcdb45983fd901f8d665ecc795e6e
				+(http://www.example.com/email)
					"markus.sabadello@gmail.com"
			$!710e4214a22c1840fc7a829b1c3fd32375e9efca
				+(http://www.example.com/email)
					"msabadello@parityinc.net"

Get one Attribute from an Entity

IdAS calls:

IEntity entity = context.getEntity("=markus");
IAttribute attribute = entity.getAttribute("http://www.example.com/someAttributeId");

Message sent by the XDI Context Provider to <url>:

=sender
	$get
		/
			=markus
				+(http://www.example.com/name)

HTTP REST:

GET on <url>/=markus/%2B(http://www.example.com/name)

Reply from the XDI endpoint:

=markus
	+(http://www.example.com/name)
		/
			$!da649486d19f8cc02350447179637cba604eff46
				+(http://www.example.com/name)
					"Markus"

Remove an Entity from the Context

IdAS calls:

IEntity entity = context.getEntity("=markus");
entity.remove();

Message sent by the XDI Context Provider to <url>:

=sender
	$del
		/
			=markus

HTTP REST:

DELETE on <url>/=markus

Reply from the XDI endpoint: (none)

Remove an Attribute from an Entity

IdAS calls:

IEntity entity = context.getEntity("=markus");
IAttribute attribute = entity.getAttribute(new URI("http://www.example.com/name"));
attribute.remove();

Message sent by the XDI Context Provider to <url>:

=sender
	$del
		/
			=markus
				+(http://www.example.com/name)

HTTP REST:

DELETE on <url>/=markus/%2B(http://www.example.com/name)

Reply from the XDI endpoint: (none)

Remove a Value from an Attribute

IdAS calls:

IEntity entity = context.getEntity("=markus");
IAttribute attribute = entity.getAttribute(new URI("http://www.example.com/email"));
IAttributeValue value = attribute.getValues().next().next();	// value is "msabadello@parityinc.net"
value.remove();

Message sent by the XDI Context Provider to <url>:

=sender
	$del
		/
			=markus
				+(http://www.example.com/email)
					/
						$!710e4214a22c1840fc7a829b1c3fd32375e9efca	<-- HIN of msabadello@parityinc.net -->

HTTP REST:

DELETE on <url>/=markus/%2B(http://www.example.com/email)//$!710e4214a22c1840fc7a829b1c3fd32375e9efca

Reply from the XDI endpoint: (none)

Change a Value of an Attribute

IdAS calls:

IEntity entity = context.getEntity("=markus");
IAttribute attribute = entity.getAttribute(new URI("http://www.example.com/email"));
Iterator<IAttributeValue> values = (Iterator<IAttributeValue>) attribute.getValues();
IAttributeValue value = values.next();	// current value is "markus.sabadello@gmail.com"
((ITypedValue) value).setData("markus@changedemail.com");

Message sent by the XDI Context Provider to <url>:

=sender
	$del
		/
			=markus
				+(http://www.example.com/email)
					/
						$!546de0b559ddcdb45983fd901f8d665ecc795e6e	<-- HIN of markus.sabadello@gmail.com -->
	$add
		/
			=markus
				+(http://www.example.com/email)
					/
						$!6ea54708b267b24988beca6adc34c4e79ed0a0b5	<-- HIN of markus@changedemail.com -->
							+(http://www.example.com/email)
								"markus@changedemail.com"

Reply from the XDI endpoint: (none)

Add a Value to an Attribute

IdAS calls:

IEntity entity = context.getEntity("=markus");
IAttribute attribute = entity.getAttribute(new URI("http://www.example.com/email"));
attribute.addSimpleValue(new URI(""), "markus@newemail.com");

Message sent by the XDI Context Provider to <url>:

=sender
	$add
		/
			=markus
				+(http://www.example.com/email)
					/
						$!690e082dc615d636abdaae2b066bdbf7e2b70057
							+(http://www.example.com/email)
								"markus@newemail.com"

HTTP REST:

PUT on <url>/=markus/%2B(http://www.example.com/email)
HTTP body contains "markus.sabadello@gmail.com" (without the quotes)

Reply from the XDI endpoint: (none)

Get the schema of the Context

IdAS calls:

String schema = IContext.getSchema();

TODO

Get Context Relations and Context Correlations

IdAS calls:

IContext.getRelationships() 

TODO

Authorization

Authorization support in IdAS maps to XDI link contracts.

TODO

Notifications

Notification support in IdAS maps to XDI links contracts.

TODO

Filters

Filter support in IdAS maps to XDI queries.

TODO

Links

• Higgins Home
• The XDI RDF Model is the current OASIS TC proposal for an RDF-based data model and addressing format for XDI. This document includes the proposed XDI RDF schema and a number of examples of XDI documents. (Note that it does not yet include the proposed XDI messaging format, which uses XDI documents as message envelopes for other XDI documents.)
• OASIS XDI TC Wiki
• Wikipedia page on XDI