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IdAS XDI Mapping

Revision as of 11:17, 9 August 2008 by Markus.sabadello.gmail.com (Talk | contribs) (Filters)

{{#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 at an XDI endpoint. It processes and applies incoming 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.

Concepts

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
  • Simple Values of an Attribute map to an XDI inner graph with XDI literals
  • Complex Values of an Attribute map to XDI references
  • 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 = '$' + '!' + hex(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

Mappings

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.

Entities

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

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

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"

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

Reply from the XDI endpoint: (none)

Attributes

Get one Attribute from an Entity

IdAS calls:

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

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

=sender
	$get
		/
			=markus
				+(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 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)

Reply from the XDI endpoint: (none)

Simple Values

Remove a Simple 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 -->

Reply from the XDI endpoint: (none)

Change a Simple 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 Simple 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	<-- HIN of markus@newemail.com -->
							+(http://www.example.com/email)
								"markus@newemail.com"

Reply from the XDI endpoint: (none)

Complex Values

Remove a Complex Value from an Attribute

IdAS calls:

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

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

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

Reply from the XDI endpoint: (none)

Add a Complex Value to an Attribute

IdAS calls:

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

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

=sender
	$add
		/
			=markus
				+(http://www.example.com/friend)
					=sergey

Reply from the XDI endpoint: (none)

Miscellaneous

Get the schema of the Context

IdAS calls:

String schema = IContext.getSchema();

Schema support in IdAS maps to XDI dictionary statements.

TODO

Get Context Relations and Context Correlations

IdAS calls:

IContext.getRelationships() 

TODO

Authentication

The Higgins authentication materials needed to open an XDI context are:

  • A Sender XRI (i-name or i-number)
  • A Private Key which is used to sign all messages

Example:

=sender
	$get
		/
			=markus
				+(http://www.example.com/name)
	$sig$rsa
		"bCbYq6EN26N1hdJTtrjvHw05X+MtNzyFKuyPMoEX/nHxzotTAlGDfHqGuUGMgWIrAtFBkre+bbrUA07gjb6do8kr5OsmOKYvfEi/rxnbEhlEPfISEP5/SWJ8auc+W8E6TOPK2bBTxTrt4+5JGIE4TjiP1IZe9l85rqOmeAY5TLZkFzxGanD01Jf4EbB8qDdNjVsQSZgW0zcqyAdi7/quqTLesxLM9m340doFdHhJxW0cdVLS5CjBU67TR1uDSMEfMpqQhEp8qfQaD/0dUif5Wr5/q+L8nz9BsBQ9tzfFhUSATYMaL1whNNWHEpoO/OGKQPADv/PJbsbN7T3dwyjlBA=="

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.

On the OASIS XDI TC there was a proposal for an XDI query language. The idea is simple: You send a $get and replace everything you don't know with $$. So if you want to have all attributes with a name attribute that has a value of "Sergey", you would do:

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

=sender
    $get
        /
            $$  <-- we don't know the subject -->
                +(http://www.example.com/name)
                    /
                        $$
                            +(http://www.example.com/name)
                                "Sergey"

Reply from the XDI endpoint:

=sergey    <-- that's what matched the $$ -->
    +(http://www.example.com/name)
        /
            $!11cac773045ffc189fa2e3ed232843d363d019c6
                +(http://www.example.com/name)
                    "Sergey"

This can be tested with the XDI Querier.

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

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