XDI Graph Discussion:$link

February 23, 2005

2

Simplified XDI graph notation

Resource

Data

Link

Backref

Nodes

ArcsXRI only

Physical

Logical

Type

Instance

Data orXMLResource

Ref

Links are shown as red lines w/labels

Refs are shown as back lines, no labels

!1001

=A

Bob

=B =C @D

!!1000

+email

@E

+phone +shoe.size +height +email +age

+alumni, !2 +home, !1 +home +primary

+work

+work

3

$link

• $link is the XDI resource that can “reify” the association between two XDI resource represented by the <link> tag

• It UML terms, it represents the association object that describes an association between two other objects

4

Association objects in UML

Object A Object BAssociation

AssociationObject

Describes theassociation

between Object A and Object B

5

Applied to XDI

Resource A Resource B<link>

$linkDescribes thelink between

Resource A and Resource B

6

Example

Resource

Data

Link

Backref

Nodes

ArcsXRI only

Physical

Logical

Type

Instance

Data orXMLResource

Ref

“Relationship object” – root of all attributes describing the link

between =A and =B

!1001

=A

Bob

=B =C @D

!!1000

@E

$link

+classmates =B, =A*Bob+friends

$link

<link>+contract

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Three patterns of $link

• =A/($link)/(=B)– Describes the relationship of two Logical

Authorities

• =A/(+type.1)*($link)/(+type.2)– Describes the relationship of two Types

• =A/(+type.1)/(instance.1)*($link)*(instance.2)– Describes the relationships of two Instances