The XDI Graph: An Overview of the Proposed XDI Schema XDI TC Face-to-Face Meeting OASIS Symposium April 29, 2004 Drummond Reed CTO, Cordance Corporation Co-Chair, OASIS XRI and XDI TCs

1 “Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it's the only thing that ever has.” -- Margaret Mead ( ) US Anthropologist, Author

2 "I would not give a fig for the simplicity this side of complexity, but I would give my life for the simplicity on the other side of complexity." -- Oliver Wendell Holmes, Jr.

3 "It’s turtles all the way down." -- Anecdotal

Part 1: The Proposed Overall Design of XDI

5 The Big Picture XNS 1.0 XNSORG OASIS XRI Gestation period for Dataweb technology 2005 XDI 1.0

6 Jamie Lewis on XRIs “Today, we use a wide variety of different mechanisms for identification, including addresses, IP addresses, phone numbers, and object identifiers. But most of these are specific to one means of interaction. None of them is persistent across the many different ways that people, applications, and devices can communicate, and so they don't function well as identifiers in the long run." -- Jamie Lewis, CEO and Research Chair, Burton Group, BetaNews, 2/5/2004

7 His second key point “Having that persistent, unique identifier is an important predicate for any trusted relationship between nodes. Without it, the trust is much more difficult, if not impossible, to achieve. The XRI specification is an attempt to solve this problem by creating a standard for abstract identifiers." -- Jamie Lewis, BetaNews, 2/5/2004

8 The mission of the XDI TC To build on the foundation of XRIs to provide a standard, generalized, extensible, domain- independent way to identify, describe, exchange, link, and synchronize data

9 An evolutionary step Abstraction Time IP/ Packets HTTP/ Web Pages SOAP/ XML Docs XDI/ XDI Docs

10 Moving complexity to a new bucket Complexity IP HTTP/ HTML SOAP/ XML XDI/ XML/XDI Addressing/ Packets  Protocols  Data Repre- sentation  Schemas  Dictionaries/ Thesauri

11 The primary value is in the delta Abstraction Time IP/ Packets HTTP/ Web Pages SOAP/ XML Docs XDI/ XDI Docs The primary value lies here – in what XDI can do that’s not easy using HTTP, XML, and SOAP

12 What’s in that delta? Persistent identification and linking –The URN problem Cross-domain data sharing –The ontology and data mapping problem Distributed data sharing controls –The security, privacy, and trust problem Generalized synchronization –The data concurrency problem

13 Proposed XDI specifications Complexity IP HTTP/ HTML SOAP/ XML XDI/ XML/XDI Addressing/ Packets TCP/IPURI XRI ProtocolsHTTPSOAPXDI Data Repre- sentation XML SchemasXDI/XML Dictionaries/ Thesauri XDI Service Dictionary

14 The Dataweb Model If every piece of data could be uniquely addressed using an XRI… …and there were a simple way to describe this in XML… …and a standard service for exchanging, linking, and synchronizing these XML documents with security and privacy controls… …you could create a trusted Web of all data… …a Dataweb.

15 Websites vs. Dataweb sites HTML Website A HTML Website B XDI Link contracts XML/ XDI Dataweb site A XML/ XDI Dataweb site B

16 Web standards vs. Dataweb standards URIsXRIs HTMLXML/XDI HTTP XDI/HTTP XDI/SOAP 100% resource addressability Common representation and linking format Common interchange protocol WebDataweb OASIS XDI TC

Part 2: The XDI Graph – Understanding the Proposed XDI Metaschema

18 The XDI metaschema The goal is a common representation format for all XRI-identifiable data Essentially a cross between the function of HTML (as a common representation format for all content) and XML (as an extensible markup language for data) A meta-schema because it is explicitly designed to describe (and optionally carry) other XML-encoded data

19 Inspiration for the proposed design Nature produces complexity by iterating simplicity Examples –DNA –Human Language –The Web The proposed XDI metaschema applies this principle to describing data and data relationships

20 The XDI Graph Authority AAuthority B Resources Link

21 The proposed XDI meta-schema Resource Link XRIData 1..* 0..1 * ** * “Turtles all the way down”

22 The name/value pair analogy name=value value name value name value name1 name2 name3 value Classic view XML encoding XDI meta-encoding step 1 XDI meta-encoding step 3: XRI synonyms permit many-to-one mapping of “names” to data values XDI meta-encoding step 2

23 Nesting resources name1 name2 name3 value name1 name2 value Nested resources have a UML composition relationship with the parent resource

24 Links name1 name2 name3 value A resource represents the authoritative source of a data value name1 name2 name3 value A link represents a cached resource instantiated at another node on the XDI graph. This cache can be anything from a 100% complete replica down to a single XRI reference

25 Nesting links name1 name2 name3 value name1 name2 value Nested links have a UML aggregation relationship with the parent resource

26 Use of the XML “Any” type name1 name2 name Main St. Seattle … The data element can contain any well-formed XML

27 The XDI graph The XDI graph is the graph of all data that is XRI-identifiable Three node types –Data (edge nodes) –Resources (authoritative paths to data) –Links (non-authoritative paths to data copies) Every XDI document is a “snapshot” of some subset of the XDI graph Most importantly, any segment of the graph can be “copied-and-pasted” to any other point

28 Addressing nodes in the XDI graph Every node is XRI-addressable because the XDI graph is a reflection of XRI syntactic structure –Authorities (XRI or URI) are the a-priori starting points –“/” (equivalent to “/.”) or “/:” represents a resource –“.” or “:” represents a link –Cross-reference syntax enables XRIs or URIs to be reused at any point in the graph

29 Mapping XRI syntax to the XDI meta-schema Resource Link XRIData 1..* 0..1 * ** * / (reassignable) or /: (persistent). (reassignable) or : (persistent) Note: this interpretation of XRI syntax applies ONLY to the proposed XDI metaschema, and not to XRIs used outside this context

30 Navigating the XDI Graph with XRIs Authority AAuthority B Resources Link

Pseudo-XML Example (see separate “XDI-Graph-Examples-v1”)

Part 3: The Proposed XDI Service Definition

33 Web standards vs. Dataweb standards URIsXRIs HTMLXML/XDI HTTP XDI/HTTP XDI/SOAP 100% resource addressability Common representation and linking format Common interchange protocol WebDataweb

34 Is XDI a Web service? Yes, XDI/SOAP is absolutely a Web service –A data-oriented service –A data mediation service –A generalized data sharing service But XDI can also be bound to other transport protocols –XDI/HTTP is “native” REST architecture for Web purists –XDI/SMTP is a solution to structured

35 XDI service definition The Dataweb model follows classic Web “REST” architecture Representational State Transfer –Roy Fielding’s PhD thesis –Posits that the success of the Web is based on transfer of URI-addressable resource representations –Representations may be linked using URIs –“Many nouns, few verbs”

36 REST operations Four verbs –GET – read resource representation –PUT – write resource representation –DELETE – remove resource representation –POST – invoke operation on resource representation Many nouns –Any resource that can be represented, i.e., any XRI

37 Proposed XDI service definition WSDL adaptation of REST –Allows binding to HTTP, SOAP, SMTP/MIME, or any other transport protocol All representations are XDI documents –Data –Forms (data requests) –Contracts (data sharing agreements) –Dictionaries (data definitions)

38 XDI forms The Dataweb equivalent of HTML forms –HTML forms are interpreted by people –XDI forms are interpreted by machines They are a way to request an XDI document from another XDI authority (“copy a branch of the XDI graph”) Forms that request controlled (private) data require data control metadata

39 XDI link contracts A link contract is an XDI document that governs the exchange of other XDI documents Directly analogous to real-world contracts that govern the exchange of goods, services, or information There is no limit to the types of controls in an XDI contract – it can describe any set of terms governing data interchange

40 Link contracts control XDI data “flow” HTML Website A HTML Website B XDI Link contracts XML/ XDI Dataweb site A XML/ XDI Dataweb site B

41 Defining link contract controls The role of the XDI Service Dictionary –Directly analogous to a legal dictionary Example: privacy controls –A link contract can associate an XDI document (a set of XRI-addressable nodes) with data usage controls –Such controls can include: References to applicable privacy policies Opt-in and opt-out permissions Data retention terms

42 Analogs to conventional directory constructs Identity, Attributes, Groups, Roles –Identity = XRI for a resource –Attributes = resources representing nested (composed) resources –Groups = resources representing linked (aggregated) resources –Roles = resources representing typed (inheritance) resources

43 XDI dictionaries XDI dictionaries are Dataweb sites designed explicitly to share “words” (XRIs) and “definitions” (XDI documents describing them) Directly analogous to real-world dictionaries Can be developed for any purpose –General dictionaries (Oxford English Dictionary) –Specialized dictionaries (Black’s Law Dictionary) –Domain specific “glossaries”

44 What’s different about XDI dictionaries? Machine-readable Machine-linkable (dictionaries can reference or link each other’s vocabulary) Can significantly automate the process of cross-domain data mapping –Human-language translations –Ontology development

45 A different view of a “semantic web” The descriptions and relationships between resources are all expressed as XRI paths through the XDI graph Common semantics are established via dynamic mapping of XRI synonyms using XDI dictionaries Vocabulary can evolve as quickly as new XRIs and XDI documents are propagated throughout the network

46 Another view – link levels Presentation Application Data Web Web servicesDataweb Links

Q & A