IdAS XDI Mapping

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Contents

Status

  • This document needs to be updated to show a representative Persona Data Model 2.0 data structure instead of the "made up" structure shown in the diagram below.
  • The endpoints are all broken at present (old parityinc, graceland links)

Introduction

This page documents the mapping between the Higgins Context 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 Attribute Service exposes an IdAS Context at an XDI endpoint. It processes and applies incoming XDI messages.

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

Mapping

Concepts

Since the Higgins Data Model is based on RDF/OWL, and XDI is also based on RDF, the basic mapping is straightforward. However, some attention has to be paid to details.

A Higgins Context can be mapped to an XDI graph using the following rules:

  • An Entity maps to an XDI subject. The XDI subject's XRI is the Entity ID cast to an XRI.
  • An Attribute maps to an XDI predicate. The XDI predicate's XRI is the Attribute ID cast to an XRI.
  • In general, each Value of an Attribute maps to an XDI subject inside an XDI inner graph. The XDI subject's XRI is a HIN (Hash I-Number) calculated from the Value.
    • If the Value is a Simple Value, then the XDI subject in the XDI inner graph has a single XDI predicate with an XDI literal. The XDI predicate's XRI is the the special $value XDI predicate.
    • If the Value is a Complex Value, then the rules for mapping the Attributes of that Complex Value apply recursively, i.e. each Attribute of the Complex Value maps to an XDI predicate.
  • Special case 1: If an Attribute contains only a single Simple Value, then that Attribute does not need an inner graph. Instead the Value maps directly to an XDI literal on the XDI predicate that represents the Attribute.
  • Special case 2: If an Attribute is an Entity Relation, then that Attribute does not need an inner graph. Instead the Values map directly to XDI references on the XDI predicate that represents the Attribute.
  • An Entity Correlation maps to an XDI statement with the special $is XDI predicate
  • The type of an Entity maps to an XDI statement with the special $is$a XDI predicate
  • The type of a Value maps to an XDI statement with the special $is$a XDI predicate

Example

Example Context diagram:

IdAS XDI.png

Example Context description:

  • The Context has three Entities =paul, =sergey and =drummond.
  • =paul has an Attribute +name, which has a single Simple Value :"Paul T.".
  • =paul has an Entity Relation +friend to =sergey and =drummond.
  • =paul has an Attribute +phone, which has two Values:
    • The first Value is a Simple Value: "+1 (617) 513 7924".
    • The second Value is a Simple Value: "+1 (781) 559 0153".
  • =paul has an Attribute +address, which has three Values:
    • The first Value is a Simple Value: "56 Kearney Rd, Needham, Massachusetts 02494, USA".
    • The second Value is a Complex Value. It has four Attributes +street, +city, +state and +zip.
      • The first Attribute has a single Simple Value: "56 Kearney Rd".
      • The second Attribute has a single Simple Value: "Needham".
      • The third Attribute has a single Simple Value: "MA".
      • The fourth Attribute has a single Simple Value: "02494".
    • The third Value is a Complex Value. It has two Attributes +line and +country.
      • The first Attribute has two Values.
        • The first Value is a Simple Value: "56 Kearney Rd".
        • The second Value is a Simple Value: "Needham, Massachusetts 2494".
      • The second Attribute has a single Simple Value: "USA".

Example Context in XDI:

=paul     <-- An Entity -->
   +name     <-- A "Special Case 1" Attribute -->
      "Paul T."     <-- A single Simple Value -->
   +friend     <-- A "Special Case 2" Attribute -->
      =sergey     <-- An Entity Relation Value -->
      =drummond     <-- An Entity Relation Value -->
   +phone     <-- An Attribute with two Values -->
      /
         $value$hash$sha$256!e5754ab606a4f0d6a3570d2c37c1f75643b9eefccf8e66e27ec77499bea8ae1d     <-- First Value of +phone: A Simple Value -->
            $value
               "+1 (617) 513 7924"
         $value$hash$sha$256!b25629ef86f5f6347f90b31225f95872982bc336ebd34c38e6533e0889bf13ca     <-- Second Value of +phone: A Simple Value -->
            $value
               "+1 (781) 559 0153"
   +address     <-- An Attribute with three Values -->
      /
         $value$hash$sha$256!07e8c548c164ea1df063e85d13a5faa04ee2e3129b571ace4360c557ba506a9c     <-- First Value of +address: A Simple Value -->
            $value
               "56 Kearney Rd, Needham, Massachusetts 02494, USA"
         $value$hash$sha$256!854d3dfca2b7388c160d301ddcad24084280c7d7bf3e2faac607b1c21917a715     <-- Second Value of +address: A Complex Value with four Attributes -->
            +street     <-- A "Special Case 1" Attribute -->
               "56 Kearney Rd"     <-- A single Simple Value -->
            +city     <-- A "Special Case 1" Attribute -->
               "Needham"     <-- A single Simple Value -->
            +state     <-- A "Special Case 1" Attribute -->
               "MA"     <-- A single Simple Value -->
            +zip     <-- A "Special Case 1" Attribute -->
               "02494"     <-- A single Simple Value -->
         $value$hash$sha$256!da4bb94a2779f74e4995fbb8a83965df2dfb9c91c63ba3a561206c33feb9d324     <-- Third Value of +address: A Complex Value with two Attributes -->
            +line     <-- An Attribute with two values -->
               /
                  $value$hash$sha$256!4e8ae563672c68cb1533ae16993a693033f1a9032e43893c3464956b8ec2109c     <-- First Value of +line: A Simple Value -->
                     $value
                        "56 Kearney Rd"
                  $value$hash$sha$256!d27ef0bac9a6830121ebc30cd911fa9672a28fa8e8bd5d63ae3ade11af519d32     <-- Second Value of +line: A Simple Value -->
                     $value
                        "Needham, Massachusetts 02494"
            +country     <-- A "Special Case 1" Attribute -->
               "USA"     <-- A single Simple Value -->
=sergey     <-- An Entity -->
=drummond     <-- An Entity -->

Hash I-Numbers for Simple Values

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 an XDI inner graph.

This pseudocode can be used to calculate a HIN for a Simple Value:

FUNCTION makeSimpleValueHin(simpleValue)

  String hin = "$value$hash$sha$256" + "!" + hex(sha256(simpleValue.lexical));
  RETURN hin;
END

Examples:

  • "Sergey" becomes $value$hash$sha$256!f3357799ddcf994ae4d759e37d58c29938419f5af9681ae65a6f0f1677b213b7
  • "Markus" becomes $value$hash$sha$256!f00b1896cf1c0569b9bdcfdde4ed948a266bae9707b3567240211efc8ffc06a0
  • "+1 (617) 513 7924" becomes $value$hash$sha$256!e5754ab606a4f0d6a3570d2c37c1f75643b9eefccf8e66e27ec77499bea8ae1d
  • "+1 (781) 559 0153" becomes $value$hash$sha$256!b25629ef86f5f6347f90b31225f95872982bc336ebd34c38e6533e0889bf13ca

Hash I-Numbers for Complex Values

Hash I-Numbers are also used to refer to individual Complex Values. Like with Simple Values, HINs for Complex Values are calculated from the Value and can then be used as an index of that Value in an XDI inner graph.

This pseudocode can be used to calculate a HIN for a Complex Value:

FUNCTION makeComplexValueHin(complexValue):

  String hin = "$value$hash$sha$256" + "!" + hex(sha256(makeComplexString(complexValue)));
  RETURN hin;
END

FUNCTION makeComplexValueString(complexValue):

  String buffer = "";
  Set attributeIds;  # a set of strings representing the attribute ids of this complex value

  FOR EACH attribute IN complexValue.attributes

    attibuteIds.push(attrIdToXri(attribute.attributeId))
  END

  FOR EACH attributeId IN sort(attributeIds)

    buffer += attributeId + ' ';
    Set simpleValuesStrings;  # a set of strings representing the simple values of this complex value
    Set complexValuesStrings;  # a set of strings representing the complex values of this complex value

    Attribute attribute = complexValue.getAttribute(attributeId)

    FOR EACH value IN attribute.values

      IF value.isSimple THEN
        simpleValuesStrings.push('"' + value.lexical + '"' + ' ')
      ELSE IF value.isComplex THEN
        complexValuesStrings.push(makeComplexValueString(value) + ' ')
      END IF
    END FOR

    buffer += concat(sort(simpleValuesStrings));
    buffer += concat(sort(complexValuesStrings));
  END FOR

  RETURN buffer;
END

Examples:

  • For the second Value of +address,
    • the result of the makeComplexValueString() function is +city{space}"Needham"{space}+state{space}"MA"{space}+street{space}"56 Kearney Rd"{space}+zip{space}"02494"{space}
    • the result of the makeComplexValueHin() function is $value$hash$sha$256!854d3dfca2b7388c160d301ddcad24084280c7d7bf3e2faac607b1c21917a715
  • For the third Value of +address,
    • the result of the makeComplexString() function is +country{space}"USA"{space}+line{space}"56 Kearney Rd"{space}"Needham, Massachusetts 02494"{space}
    • the result of the makeComplexHin() function is $value$hash$sha$256!da4bb94a2779f74e4995fbb8a83965df2dfb9c91c63ba3a561206c33feb9d324

Test endpoints

The following XDI endpoints are available for testing:

IdAS Attribute Service

Native XDI Endpoints

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.

Entities

List all Entities

This example gets all Entities in the Context.

IdAS calls:

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

Message sent by the XDI CP:

=sender
	$get

Reply from the Attribute Service / native XDI endpoint:

=paul
=sergey
=drummond

Get one Entity from the Context

This example gets the Entity =paul in the Context.

IdAS calls:

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

Message sent by the XDI CP:

=sender
   $get$a$xsd$boolean
      /
         =paul

Reply from the Attribute Service / native XDI endpoint:

$true

Remove an Entity from the Context

This example removes Entity =paul from the Context.

IdAS calls:

IEntity entity = context.getEntity("=paul");
entity.remove();
context.applyUpdates();

Message sent by the XDI CP:

=sender
   $del
      /
         =paul

Reply from the Attribute Service / native XDI endpoint: (none)

Attributes

List all Attributes from an Entity

This example gets all Attributes of the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
Iterator<IAttribute> attributes = entity.getAttributes();

Message sent by the XDI CP:

=sender
   $get
      /
         =paul
  • After sending the message, the XDI CP remembers the HINs of the individual values, in order to be able to refer to them later

Reply from the Attribute Service / native XDI endpoint:

=paul
   +name
   +friend
   +phone
   +address

Get one Attribute from an Entity

This example gets the Attribute +phone of the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));

Message sent by the XDI CP:

=sender
   $get$a$xsd$boolean
      /
         =paul
            +phone
  • After sending the message, the XDI CP remembers the HINs of the individual values, in order to be able to refer to them later

Reply from the Attribute Service / native XDI endpoint:

$true

Remove an Attribute from an Entity

This example removes the Attribute +phone from the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));
attribute.remove();
context.applyUpdates();

Message sent by the XDI CP:

=sender
   $del
      /
         =paul
            +phone

Reply from the Attribute Service / native XDI endpoint: (none)

Values

List all Values from an Attribute

This example gets all Values of the Attribute +phone on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));
Iterator<IAttributeValue> values = attribute.getValues();

Message sent by the XDI CP:

=sender
   $get
      /
         =paul
            +phone
  • After sending the message, the XDI CP remembers the HINs of the individual values, in order to be able to refer to them later

Reply from the Attribute Service / native XDI endpoint:

=paul
   +phone
      /
         $value$hash$sha$256!e5754ab606a4f0d6a3570d2c37c1f75643b9eefccf8e66e27ec77499bea8ae1d     <-- First Value of +phone: A Simple Value -->
            $value
               "+1 (617) 513 7924"
         $value$hash$sha$256!b25629ef86f5f6347f90b31225f95872982bc336ebd34c38e6533e0889bf13ca     <-- Second Value of +phone: A Simple Value -->
            $value
               "+1 (781) 559 0153"


Simple Values

Remove a Simple Value from an Attribute

This example removes the Simple Value +1 (781) 559 0153 from the Attribute +phone on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));
ISimpleAttrValue value = (ISimpleAttrValue) attribute.getValues().next().next();	// value is "+1 (781) 559 0153"
value.remove();
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the value (if it does not know it already)

Message sent by the XDI CP:

=sender
   $del
      /
         =paul
            +phone
               /
                  $value$hash$sha$256!b25629ef86f5f6347f90b31225f95872982bc336ebd34c38e6533e0889bf13ca	<-- HIN of +1 (781) 559 0153 -->

Reply from the Attribute Service / native XDI endpoint: (none)

Modify a Simple Value of an Attribute

This example changes the Simple Value +1 (781) 559 0153 to +1 234 56789 on the Attribute +phone on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));
ISimpleAttrValue value = (ISimpleAttrValue) attribute.getValues().next().next();	// value is "+1 (781) 559 0153"
value.setData("+1 234 56789");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the value (if it does not know it already)
  • After sending the message, the XDI CP re-calculates the HIN of the value, in order to be able to refer to it later

Message sent by the XDI CP:

=sender
   $mod
      /
         =paul
            +phone
               /
                  $value$hash$sha$256!$!b25629ef86f5f6347f90b31225f95872982bc336ebd34c38e6533e0889bf13ca	<-- HIN of +1 (781) 559 0153 -->
                     $value
                        "+1 234 56789"

Reply from the Attribute Service / native XDI endpoint: (none)

Add a Simple Value to an Attribute

This example adds the Simple Value +1 987 65432 to the Attribute +phone on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+phone"));
ISimpleAttrValue value = attribute.addSimpleValue(ITypedValue.STRING_TYPE_URI, "+1 987 65432");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the value

Message sent by the XDI CP:

=sender
   $add
      /
         =paul
            +phone
               /
                  $value$hash$sha$256!bb4d1ce368e89f0f5c4bfb867cd4b0437eadfa7aa559f9b49bf359bc5903a282	<-- HIN of +1 987 65432 -->
                     $value
                        "+1 987 65432"

Reply from the Attribute Service / native XDI endpoint: (none)

Complex Values

Remove a Complex Value from an Attribute

This example removes a Complex Value from the Attribute +address on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+address"));
ISimpleAttrValue value = (ISimpleAttrValue) attribute.getValues().next().next();	// second value
value.remove();
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the value (if it does not know it already)

Message sent by the XDI CP:

=sender
   $del
      /
         =paul
            +address
               /
                  $value$hash$sha$256!854d3dfca2b7388c160d301ddcad24084280c7d7bf3e2faac607b1c21917a715	<-- HIN of a complex value -->

Reply from the Attribute Service / native XDI endpoint: (none)

Add a Complex Value to an Attribute (Example 1)

This example adds a Complex Value to the Attribute +address on the Entity =paul. The Complex Value has four Attributes.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+address"));
IComplexAttrValue value = attribute.addComplexValue(URI.create(BasicComplexValue.ATTR_VALUE_TYPE_URI_STR)));
IAttribute subAttributeCity = value.addAttribute(URI.create("xri://+city"));
IAttribute subAttributeState = value.addAttribute(URI.create("xri://+state"));
IAttribute subAttributeStreet = value.addAttribute(URI.create("xri://+street"));
IAttribute subAttributeZip = value.addAttribute(URI.create("xri://+zip"));
subAttributeCity.addSimpleValue(ITypedValue.STRING_TYPE_URI, "Needham");
subAttributeState.addSimpleValue(ITypedValue.STRING_TYPE_URI, "MA");
subAttributeStreet.addSimpleValue(ITypedValue.STRING_TYPE_URI, "56 Kearney Rd");
subAttributeZip.addSimpleValue(ITypedValue.STRING_TYPE_URI, "02494");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the values, in order to be able to refer to them later

Message sent by the XDI CP:

=sender
   $add
      /
         =paul
            +address
               /
                  $value$hash$sha$256!854d3dfca2b7388c160d301ddcad24084280c7d7bf3e2faac607b1c21917a715
                     +city
                        "Needham"
                     +street
                        "56 Kearney Rd"
                     +state
                        "MA"
                     +zip
                        "02494"

Reply from the Attribute Service / native XDI endpoint: (none)

Add a Complex Value to an Attribute (Example 2)

This example adds a Complex Value to the Attribute +address on the Entity =paul. The Complex Value has two Attributes.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+address"));
IComplexAttrValue value = attribute.addComplexValue(URI.create(BasicComplexValue.ATTR_VALUE_TYPE_URI_STR)));
IAttribute subAttributeLine = value.addAttribute(URI.create("xri://+line"));
IAttribute subAttributeCountry = value.addAttribute(URI.create("xri://+country"));
subAttributeLine.addSimpleValue(ITypedValue.STRING_TYPE_URI, "Needham, Massachusetts 02494");
subAttributeLine.addSimpleValue(ITypedValue.STRING_TYPE_URI, "56 Kearney Rd");
subAttributeCountr.addSimpleValue(ITypedValue.STRING_TYPE_URI, "USA");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the values, in order to be able to refer to them later

Message sent by the XDI CP:

=sender
   $add
      /
         =paul
            +address
               /
                  $value$hash$sha$256!da4bb94a2779f74e4995fbb8a83965df2dfb9c91c63ba3a561206c33feb9d324
                     +line 
                        /
                           $value$hash$sha$256!d27ef0bac9a6830121ebc30cd911fa9672a28fa8e8bd5d63ae3ade11af519d32
                              $value
                                 "Needham, Massachusetts 02494"
                           $value$hash$sha$256!4e8ae563672c68cb1533ae16993a693033f1a9032e43893c3464956b8ec2109c
                              $value
                                 "56 Kearney Rd"
                     +country
                        "USA"

Reply from the Attribute Service / native XDI endpoint: (none)

Modify a Simple Value of a Complex Value (Example 1)

This example changes the Simple Value MA to Massachusetts on the Attribute +state on the second Value of the Attribute +address on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+address"));
IComplexAttrValue value = (IComplexAttrValue) attribute.getValues().next().next();	// second value of +address
IAttribute subAttribute = value.getAttribute(URI.create("xri://+state"));
ISimpleAttrValue subValue = (ISimpleAttrValue) subAttribute.getValues().next();		// value is "MA"
value.setData("Massachusetts");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the values (if it does not know them already)
  • After sending the message, the XDI CP re-calculates the HIN of the values, in order to be able to refer to them later

Message sent by the XDI CP:

=sender
   $mod
      /
         =paul
            +address
               /
                  $value$hash$sha$256!854d3dfca2b7388c160d301ddcad24084280c7d7bf3e2faac607b1c21917a715	<-- HIN of second value of +address -->
                     +state
                        "Massachusetts"

Reply from the Attribute Service / native XDI endpoint: (none)

Modify a Simple Value of a Complex Value (Example 2)

This example changes the Simple Value Needham, Massachusetts 02494 to Needham, MA 02494 on the Attribute +line on the third Value of the Attribute +address on the Entity =paul.

IdAS calls:

IEntity entity = context.getEntity("=paul");
IAttribute attribute = entity.getAttribute(URI.create("xri://+address"));
IComplexAttrValue value = (IComplexAttrValue) attribute.getValues().next().next().next();	// third value of +address
IAttribute subAttribute = value.getAttribute(URI.create("xri://+line"));
ISimpleAttrValue subValue = (ISimpleAttrValue) subAttribute.getValues().next();		// value is "Needham, Massachusetts 02494"
value.setData("Needham, MA 02494");
context.applyUpdates();
  • Before sending the message, the XDI CP calculates the HIN of the values (if it does not know them already)
  • After sending the message, the XDI CP re-calculates the HIN of the values, in order to be able to refer to them later

Message sent by the XDI CP:

=sender
   $mod
      /
         =paul
            +address
               /
                  $value$hash$sha$256!da4bb94a2779f74e4995fbb8a83965df2dfb9c91c63ba3a561206c33feb9d324	<-- HIN of third value of +address -->
                     +line
                        /
                           $value$hash$sha$256!d27ef0bac9a6830121ebc30cd911fa9672a28fa8e8bd5d63ae3ade11af519d32 <-- HIN of Needham, Massachusetts 02494 -->
                              $value
                                 "Needham, MA 02494"

Reply from the Attribute Service / native 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
		/
			=paul
				+address
	$sig$rsa
		"bCbYq6EN26N1hdJTtrjvHw05X+MtNzyFKuyPMoEX/nHxzotTAlGDfHqGuUGMgWIrAtFBkre+bbrUA07gjb6do8kr5OsmOKYvfEi/rxnbEhlEPfISEP5/SWJ8auc+W8E6TOPK2bBTxTrt4+5JGIE4TjiP1IZe9l85rqOmeAY5TLZkFzxGanD01Jf4EbB8qDdNjVsQSZgW0zcqyAdi7/quqTLesxLM9m340doFdHhJxW0cdVLS5CjBU67TR1uDSMEfMpqQhEp8qfQaD/0dUif5Wr5/q+L8nz9BsBQ9tzfFhUSATYMaL1whNNWHEpoO/OGKQPADv/PJbsbN7T3dwyjlBA=="

Access control

Access control 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 CP:

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

Reply from the Attribute Service / native XDI endpoint:

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

This can be tested with the XDI Querier.

Links

  • 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