The XDI Graph Basics

1. The XDI Graph Basics The XDI Universal Graph is the logical data model by which resources and their associated data are discovered, identified and accessed on the Dataweb. This does not imply anything about the native data schema or physical storage mechanism!! Any resource that can be associated with an XRI is a candidate for inclusion in the XDI Graph (although XDI does place some constraints on the structure of the XRI)

2. The XDI Graph Basics • The proposed XDI Universal Schema stipulates that the XRI element identifying an XDI Resource be made up of a combination of 4 subelements: • Physical Authority • Logical Authority • Type • Instance

3. The XDI Graph Basics The first Graph Element is Resource Nodes. These are depicted as black circles. A Resource Node is any point in the XDI Graph that is the parent of either another Resource Node, a Link Node, or a Data Node. It can also contain a reference to another Resource Node. Resource Nodes serialize into Resource Elements in the XDI Universal Schema !!1010 Black lines depict authoritative relationships. Authoritative Relationships are arcs where the Child Node is wholly dependent for it’s existence on the Parent Node. If the parent is deleted the child is also deleted. (This is analogous to a UML Composition Relationship.)

4. The XDI Graph Basics It is important to note that ‘labels’ (XRIs) actually name the arcs (lines) between nodes not the nodes themselves. Space permitting I always try to place the labels as close as I can to the arrow head of an arc. !!1010 =andy Resource Nodes at any level MUST have ONLY ONE authoritative parent at the level above. +Email home Data Nodes are depicted in green and CANNOT have children. They are ‘Terminal Nodes’ XMLResource Nodes are also Terminal Nodes and are also depicted as green dots. ad@ootao.com

5. The XDI Graph Basics A red dotted line shows a Reference (Ref). A Ref is a non-authoritative relationship. It is a way of saying.. “My value is the same as another node at this level. Whatever he says goes”. It denotes equivalence. The blue dotted line is a Backref. A Backref is the mechanism by which a node knows (or shows) that it is referenced. !!1010 @ooTao =andy +Email +Email • In this example the ooTao contact email is delegated to Andy’s work email so if Andy’s work email changes, ooTao’s contact email will still be up to date. • Someone executing an XDI_get() for ooTao’s contact email wouldn’t NEED to know that there is a Ref involved as the path to the data could be expressed as: • xri://@ooTao/(+Email)/contact contact work ad@ootao.com

6. The XDI Graph Basics !!1010 These NOTES in red will show up from time to time. These are statements that we believe to be ‘Theorems’ about the XDI Graph ( and should therefore be imposed by the Schema whereever possible). I highlight them as we are actively looking for the exceptions that will disprove the rule. @ooTao =andy +Email +Email contact contact work NOTE: Because a Ref denotes equivalence it can ONLY go horizontally, i.e., across a level of the graph. ad@ootao.com

7. The XDI Graph Basics !!1010 @ooTao =Andy • The red dot is a Link Node. Links denote aggregation or inclusion. (This is analogous to a UML Aggregation Relationship.) • A red dot is similar to the English language concept of ‘includes’; in this example @ooTao’s contact email includes =Andy’s work email, it can also include other values. • One way to express the XRI of ooTao’s contact email is therefore; • xri://@ooTao/(+Contact)/email*(=Andy/(+Email)/work) +Contact +Email email work =Andy/(+Email)/work ad@ootao.com

8. Delegation Syntax A’s Paths to C: xri://=A*B/C You may alternately use the =B synonym: xri://=A*(=B)/C !!1011 !!1012 =B =A XRI delegation syntax (* or !) is used when one authority wants to provide a link to data at another authority… It looks like C is coming from =A (has a path rooted in =A), but C comes from B. =B B, =B C Resources representing Physical Authority nodes – the “root” of each instance of an XDI graph – can be linked just like any other level. In this case the Refs shown are links from a global registry representing the XRI 2.0 global context symbol (GCS) “!”. This registry has assigned the i-numbers “!1012” and “!1011” to these two Physical Authorities, so the absolute XRI paths are “!!1012” and “!!1011”.

9. Versioning Syntax !!1010 =Andy +Email Versioning Syntax is a form of delegation that can occur at any level. It represents an XRI cross-reference to the type “$v” (for version), followed by a version instance. !2 Primary !1 $v/2 $v/1 Ad@ooTao.com Ad@convoii.net

10. Virtual Nodes • We propose that XDI supports some special ‘Virtual Node’ syntax; one example of the ‘Virtual Node’ syntax is the $Current system word. This is an addressable node at the Version level that signifies ‘get the latest version’ . • This is a virtual node because there does not actually need to be any node named $Current. For example; • xri://=Andy/(+Email)/Primary/($Current) • should return the $v/2 node. !!1010 =Andy +Email !2 Primary !1 $v/2 $v/1 Ad@ooTao.com Ad@convoii.net

11. Building the Dataweb To start building any “tree” (instance) of the XDI graph “forest” (Dataweb), you first need a Physical Authority on which to root it. This Resource Node represents the network endpoint through which other nodes on the graph are addressable. Like any XDI Resource, it may have multiple XRI synonyms. This Physical Authority represents an i-broker addressable both via an abstract global independent XRI (!!1010) and via two concrete URIs based on DNS domain names. A Physical Authority could be any network-addressable endpoint, from a server farm to a cell phone to a thermostat. The Dataweb abstracts all Physical Authorities as peers, just like all IP addresses are peers. !!1010, http://xdi.example.com,https://xdi.example.com @ooTao

12. Building the Dataweb • A Physical Authority registers and hosts Logical Authorities (similar to the way a PC can have multiple Users). • A Logical Authority can in turn register other Logical Authorities. Note that while the i-number “!A2B3” for the second Logical Authority above is assigned by the Physical Authority !!1010, the i-name “andy” is assigned by the Logical Authority “@ooTao”. Thus there are now 3 XRI paths to this new Resource Node: • xri://!!1010/!A2B3 • xri://!!1010/(@ooTao*andy)xri://@ooTao*andy !!1010 !A2B3,@ooTao*andy @ooTao andy

13. Building the Dataweb Here the @ooTao authority has resources that are about ooTao. It has delegated authority for Andy and Steven’s data to other (local) Logical Authorities. !!1010 steven !A2B3,@ooTao*steven @ooTao !A2B4,@ooTao*andy andy +Phone +Email +Email +Phone +Email Support Admin Work Cell Primary Primary

14. Building the Dataweb If Steven now registers a global i-name, =Steven, we simply add a synonym at the node. This synonym represents a reference from the Logical Authority represented by the “=” registry. !!1010 steven !A2B3,@ooTao*steven,=Steven @ooTao !A2B4 andy +Phone +Email +Email +Phone +Email Admin Work Cell Primary Primary

15. Link Contracts One of the primary goals of XDI is to provide CONTROLLED access to data. The mechanism for control is establishing ‘Link Contracts’ between logical authorities that define ‘rules of engagement’. In order to make data accessible via an XDI Service one must create Link Contract Templates. Link Contracts are used to establish “Rights Paths” to data. NOTE: Any Logical Authority can only respond to requests on data (get, set, etc…) on Nodes under it’s own authority. The establishment of a ‘Rights Path’ is the process of establishing a XRI from one Logical Authority Node to a section of the XDI graph under another Logical Authority via an association node. If Steven only had his one piece of data, what might his Link Contract Template look like?... (next slide) !!1010 =Steven +Email Home

16. Link Contracts The first step in establishing a Link Contract Template is creating a permission path to the data. In this example the Private contract permissions an XDI Get path to =Stevens Home email via =Steven’s Personal Dataset. This example is a little simplistic as it doesn’t have any versioning syntax. See the next slide to see a more realistic version of what a Contract Template might look like. !!1010 =Steven +Email $Contracts $Dataset Private Home Personal TODO: Somewhere there should be a $Policies node that can be linked into the contract that stipulates the policies governing the sharing of this data. $Get Home

17. Link Contracts This graph section is setup so that the Personal Dataset and the Private Contract can both be independently versioned. !!1010 =Steven Here version 1 of the Private Contract permissions Get on the Personal Dataset and version 2 permissions both Get and Set on the same dataset. In this example $Get is repeated in both versions of the contract, so we theorize that there may be ‘delta’ syntax that would let v2 reference v1 and specify only the differences between them. $Dataset +Email $Contracts $v/1 Personal Private $Get Home Home $Get $v/1 $v/2 $Set

18. Link Contracts In order to show ‘permissioning’ we need another Logical Authority to ‘permission’ I am intentionally showing a case where both entities are at the same Physical Authority so we don’t (yet) have to deal with replication across Physical Authorities. !!1010 =Steven =Andy +Email +Email $Contracts In order to save space and simply illustrate the concepts I have gone back to the simple, non-versioned, depiction of the Link Contract Template. $DataSet Private Home Personal Work $Get

19. Link Contracts By adding the $Assoc (association) node we are saying that =Steven has a relationship with =Andy. The link between the =Steven/($Assoc)/(=Andy) node and the =Steven/($Contracts)/Private node establishes the contract instance that specifies the permissions. Now =Andy CAN access =Stevens data but hasn’t yet. !!1010 =Steven =Andy +Email +Email $Contracts $Dataset $Assoc Private =Andy Home Personal Work $Get

20. Link Contracts When =Andy agrees to the contract, =Andy’s digital signature of the contract is captured within =Stevens graph and =Andy creates an association node that completes the creation of the Rights Path. !!1010 =Steven =Andy $Assoc +Email +Email $Contracts $Dataset $Assoc $Sig Private =Andy Home Personal Work (=Steven/($Assoc)/(=Andy)) $Get =Andy Signed copy of the contract

21. Link Contracts The Rights path explicitly states the privileges to the Data Node (# 1 from Andy’s perspective and #2 from =Steven’s perspective) 1) xri://=Andy/($Assoc)/((=Steven/$Assoc/(=Andy))*($Contracts/Private))*($Get)*(=Steven/(+Email)/Home)) 2) xri://=Steven/$Assoc/(=Andy)*($Contracts/Private)*($Get)*(=Steven/(+Email)/Home)) !!1010 =Steven =Andy $Assoc +Email +Email $Contracts $Dataset $Assoc $Sig Private =Andy Home Personal Work $Get (=Steven/$Assoc)/(=Andy)) =Steven/(+Email)/Home $Contract/Private =Andy Signed copy of the contract

22. TO DO: The Following slides are place holders for functional areas that we still need to consider in depth. I consider these headings future sections that may each be several slides in length.

23. Link Contracts – More Complex Example The Biz Card contract permissions an Entity to Get ‘Support Phone’ and ‘Work Email’. What would I do if I want to permission the Admin contract to Get the same 2 thing AND Set ‘Work Email’? Option 1) Have 3 Links from Admin/($V/1), one that Refs each of the permission nodes. You could then link an $Assoc node to just that contract. Option 2) Have 1 Link under Admin/($V/1) that permissions Set for the ‘Work Email’ node. You would then need to link an $Assoc node to BOTH contract to provide all the permission. Option 3) Have 1 Link under Admin/($V/1) that permissions Set for the ‘Work Email’ node and add a Link at the Instance level from the Admin contract to the Biz Card contract. You could then link an $Assoc node to just the Admin contract to get all the permissions.

24. Link Contracts – Permissioning a Community

25. Resolving Synonyms – Unifying the Graph

26. Removing a path - $Deleted?

27. Delta Syntax - $Include and $Exclude?

28. Questions: • Is, and if so how, authentication expressed in the XDI Graph? • Should +Type words (Dictionary Words) be constrained to Singular or Plural, and if yes, which? • Should Instance words be Upper or Lower case? (Convention? Rule? Who Cares?) • Should $Invitations be part of the XDI Protocol or should it be delegated to the application layer?