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XDI Graph PatternsOASIS XDI TC Submission

Drummond Reed2012-02-06

This document contains illustrations of basic XDI graph patterns:

1. I-names, i-numbers, and synonyms: XDI statements used to assert multiple XRIs for the same logical resource

2. Local graphs and XDI discovery: statements that enable the global XDI graph to be distributed, discovered, and navigated across multiple locations on the network

3. Social graphs: relationships between XDI authorities

4. Literal contexts and versioning: contexts that accept a single data value and can describe versioning of that value

5. Simple contexts and ordering: contexts that represent a one-dimensional array of literal contexts and can describe ordering and typing of those values

6. Complex contexts: contexts that represent a two-dimensional array of literal contexts, simple contexts, and other complex contexts

7. Personas and roles: complex contexts and relations that model contextual identity for individuals

8. Link contracts: contexts used for XDI authorization

9. Policy expression: a context with conditional logic for rules evaluation

10. Messages: XDI graphs used in the XDI protocol

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XDI Graph Notation

Example

Context node: Represents any logical context (see next page)

Contextual arc: Uniquely identifies a root or context node

Relational arc: Non-uniquely links root or context nodes

Terminal node: Represents a leaf node containing data

Root node: Represents the root context of an XDI graph

Literal arc: Singleton arc that identifies a terminal node

contextual

contextual

contextual

root

“value”

contextualrelational

literal

relational

root

contextual

“value”literal

contextterminal

context

context

context

terminal

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Node hierarchy

Node

Terminal Context Root

Literal Ordinal ComplexSimple

Terminal nodes are the leaf points of the graph – the ones containing the raw data

Root nodes are the starting points of the

full 3-dimensional XDI graph

Literal contexts are 0-dimensional name/value pairs

name value

Ordinal contexts are 0-dimensional order/reference pairs

order ref

Simple contexts are 1-dimensional arrays of literal and ordinal contexts

instance value

instance value

instance value

order ref

order ref

order ref

name

Complex contexts are 2-dimensional arrays of literal, simple, and complex contexts

Complexity

I-names, i-numbers, and synonyms

=!0999.a7b2.25fd.c609

!1

4

=abc

()

=abc

=!0999.a7b2.25fd.c609

=!0999.a7b2.25fd.c609!1

+garden

+pea-patch

=!0999.a7b2.25fd.c609+garden

=!0999.a7b2.25fd.c609+pea-patch

The top two i-names are synonyms for the bottom i-number

Every XDI node has exactly one XRI address. A canonical equivalence relationship between two XDI context nodes (i.e., that they represent the same logical resource) may be declared using a $is relational arc. The inverse relation is $is$is. When navigating the graph, an XDI processor is required to redirect to the target node of a $is relation before continuing.

(http://xdi.example.com/=!0999.a7b2.25fd.c609)

These XRI cross-references are logically equivalent addresses for the local root of this graph

(=!0999.a7b2.25fd.c609)$is$is

$is

$is$is

The XRI =abc, an i-name, is a synonym for the XRI =!0999.a7b2.25fd.c609, an i-number

$is$is

Local graphs and XDI discovery

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()

The XDI global graph is a single logical graph of which subsets are distributed across multiple locations on the network (clients, servers, databases, etc.) Each subset, called a local graph, begins with a local root node, expressed as an empty XRI cross-reference, (). A local graph may include XDI statements about the locations of other local graphs. This enables XDI clients to perform XDI discovery: navigation of the global graph by making XDI queries across a chain of local graphs.

(=!0222.e3f2.76cb.904a)

(@!0111.db4a.e317.7a12)

“http://xdi.example/com/@!0111.db4a.e317.7a12”

!

“http://xdi.example/com/=!0222.e3f2.76cb.904a”

This local graph contains two other roots describing the URIs of two other local graphs

$uri

!

$uri

The $uri context is a property of a root

$is$is

“http://xdi.example/com/=!0111.7af3.65d5.8cb7”

!

$uri

(=!0111.7af3.65d5.8cb7)

The XDI authority for this local graph is asserted using a synonym

!1

!1

!1

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Social graphs

=abc

(http://facebook.com)

=xyz

+teammate

=abc is a teammate of =xyz in a Seattle soccer context

=abc is best friends with =xyz

=abc is friends with =xyz in the Facebook context

=abc

=xyz

+seattle

+best+friend

=xyz

+friend

+soccer

=xyz

(http://facebook.com)

(http://facebook.com)=xyz

+seattle

+seattle+soccer

+seattle+soccer=xyz

Social graph expressed at the (=!1111) local graph, for which =abc is the authority

$is$is() (=!1111) (=!1111)

=!1111

$is

+seattle+soccer=!2222

=!2222

=!2222 $is

$is

=!2222 $is

=!1111

=!2222

(http://facebook.com)=xyz

(http://facebook.com)=!2222

XDI graphs can also express the relationships between XDI authorities in different contexts. This example illustrates the relationship between =abc (i-number =!1111) and =xyz (i-number =!2222) in a global context, in a Facebook context, and in a Seattle soccer context.

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Literal contexts and versioning

=!1111

“33”

+age

!

“2010-10-10T11:12:13Z”!

$v

!1

“32”!

“2010-09-09T10:11:12Z”

$d

!2

Literal context +age

Literal value

Versioning subgraph

First version context

First version datestamp

Second version, which is also the current version

=!1111=!1111+age

=!1111+age$d

=!1111+age$v

=!1111+age$v!1

()

$is

$d

!

First version value

Datestamp subgraph

$v

=!1111+age$v!2

A literal context is the first order of complexity in an XDI graph: a context node that has a single literal arc to a terminal node. By definition a literal context has exactly one instance. However a literal context may contain other contexts describing it (subproperties). The diagram below illustrates two standard XDI subproperties: datestamping (also a literal context) and versioning (a complex context).

=!1111+age$v!1$d

=abc=abc

$is

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Simple contexts and ordering

=abc

+tel

“+1.206.555.1111”!

=abc()

!1

!2

“+1.206.555.2222”!

*2

*1=!1111+tel

=!1111+tel!1

=!1111+tel!2

=!1111+tel!2$d$d

=!1111+tel!2$v$v

…=!1111+tel$v

$v

…

+home

+home+fax

+work

A simple context is the second order of complexity in an XDI graph: a context that represents a set of literal contexts of the same type and optionally ordinals expressing their order. Each instance in a simple context is a literal context. The example shown below is a phone number. Two instances are shown, =abc+tel!1 and =abc+tel!2. The i-numbers (!1 and !2) persistently identify each instance within the set. Ordinal contexts with i-names (*1 and *2) assert the unique order of these instances. Relational arcs describe the non-unique type of each instance, e.g., +home, +home+fax, and +work.

Literal context version subgraph – reflects changes to literal values only

Simple context version subgraph – represents changes to the simple context graph only

=!1111+tel$d$d

… …

$is

$is

=!1111+tel*2

=!1111+tel*1

Two ordinal contexts, =abc+tel*1 and =abc+tel*2, assert the order of the two phone number instances

=!1111

=!1111

$is

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Complex contexts

+passport

!

!1

!2

=!1111+passport

=!1111+passport!1

$d

$v

…=!1111+passport$v

$v

…

+ca

+nz

A complex context is the third order of complexity in an XDI graph: a context that represents a set of literal contexts, simple contexts, and complex contexts. Each instance of a complex context is another complex context. The example shown below is a passport. Two instances are shown, =abc+passport!1 and =abc+passport!2. (Ordering of these instances is not shown in this diagram, but uses the same ordinal pattern as with simple contexts.)

Simple context version subgraph – reflects changes to the simple context graph only

Complex context version subgraph – represents changes to the complex context graph only

“2005-01-01T00:00:00Z”

“Canada”

“987654321”

“2010-10-01T00:00:00Z”

“New Zealand”

“123456789”

=!1111+passport$d

$d

……

!

!

!

!

!

+country

+num

+expires

=!1111+passport!1+country

+country

+num

$d

$v

…

Literal context version subgraph – reflects changes to the literal value only

…=!1111+passport!2$d$d

=!1111+passport!2$d$v

=!1111+passport!2+country

=!1111+passport!2

=abc=abc

()

=!1111

$is=!1111 $is

$is

+expires

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Personas and roles

!1

!2

=!1111!1

+home

+work

Personas are an example of using complex contexts to model the identity of a person. In the example below, the person =!1111 (aka =abc) has two personas, =!1111!1 and =!1111!2. Each of these is an instance of =!1111. @!4444 (aka @example.co) is a company in which the =!1111!2 persona plays the role of president.

+president is a role that the persona =!1111!2 plays in the context of company @!4444

=!1111!2

=abc=abc

()

=!1111

$is

=!1111

$is

$is

“33”

+age

!

=!1111+age($)

@!4444

@!4444

@example.co

@example.co

$is+president

=!1111!1 and =!1111!2 are personas of =!1111 that enable =!1111 to control the sharing of portions of =!1111’s personal graph

The ($) variable relation allows graphs to be included in other graphs – in this case, the =!1111!2 persona includes =!1111+age

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Link contracts (1)

This root link contract permits the XDI subjects to which it is assigned to perform all XDI operations on the local graph

A link contract is a complex context used for XDI authorization. A link contract is defined by a$do context. Shown below is the “bootstrap” link contract in a graph, called a root link contract: a $do child of the root node. The $all relation that points back to the root asserts that the assignee(s) of this contract have “root access”, i.e., permission perform all XDI operations on the entire local graph.

=!0999.a7b2.25fd.c609

=abc

()

=abc

=!0999.a7b2.25fd.c609

(=!0999.a7b2.25fd.c609)

$is

$is$is

$do$do

(=!0999.a7b2.25fd.c609)

$all

$is$do

$is$do is the relation used to explicitly assign the permissions of a link contract to one or more XDI subjects

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Link contracts (2)

!1

!2

=!1111!1

+home

+work

This diagram shows the addition of a link contract to the Personas and Roles diagram shown earlier. This link contract, created by =!1111 to control access to his/her =!1111!2 persona, gives the organization @!4444 $get (read) permission on that persona.

=!1111!2

=abc=abc

()

=!1111

$is

=!1111

$is

$is

“33”

+age

!

=!1111+age($)

@!4444

@!4444

@example.co

@example.co

$is+president

This link contract gives the assignee(s) permission to do an XDI $get operaton on the =!1111!2 persona, i.e., read anything in its subgraph

$do

$get

$is$do

The $is$do relation assigns this link contract to @!4444, which means people from that company will be able to access the =!1111!2 persona

Policy expression

!2

$do

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$if begins the policy expression branch of a link contract

$and branches group policy instances that must all evaluate to true

$not branches group policies that must evaluate to false

(=!1111)

$or branches group policies of which at least one must evaluate to true

=!1111

$is$is

$if

$and

$or

$not

“{policy}”!

!1

“{policy}”!

!1

“{policy}”!

!2

“{policy}”!

!1

Policy expression is handled by the $if branch of link contracts. The three policy contexts are $and (all policies must be satisfied), $or (at least one policy must be satisfied), and $not (all policies must not be satisfied).

Link contract

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Messages

(=!2222)

$do

$get

$add

“to” XDIlocal graph

Message instance

Message operations

Message envelope

“2010-12-22T22:22:22Z”

$d

!1234

(=!2222)

=!1111

=!1111$msg

Message datestamp

Message context

()

$msg

=!1111

“from” XDI authority (sender)

=!1111$msg!1234

=!1111$msg!1234$d

=!1111$msg!1234$do

(=!1111)

$is$is“from” XDI local graph

=!2222

=!2222!1$do

!1

=!2222

(=!1111)

!

(!3)(=!1111)(!3)

XDI messages are XDI graphs sent from one XDI local graph (the “from” graph) to another local graph (the “to” graph) to perform an XDI operation (e.g., $get, $add, $mod, $del, $move, $copy). Every message must reference the link contract that authorizes the operation it is requesting. Note that the $add relation records the source graph for auditing purposes.

$get$do

$is()

Every message must include a $do reference to the link contract that authorizes the operation it is requesting, e.g., this message references the =!2222!1$do link contract for $get permission on the =!2222!1 persona

$do

$is$do

=!2222!1