This page is where the TC develops and harmonizes definitions of terms that are used in the XDI 1.0 specifications. Definitions developed here will be incorporated into the Docbook file of glossary definitions used by all specs.

XDI Graph Model

XDI graph: A collection of subject-predicate-object statements, conforming to the ABNF rules in the XDI Core specification, that represents a labeled, directed acyclic graph in which every node is uniquely addressable through a directed rooted tree, or what XDI calls a "semantic tree". Every XDI statement corresponds to exactly one labeled arc in the graph and vice versa.

XDI identifier: The label of any arc in an XDI graph. XDI identifiers for contextual arcs must be unique in the context in which they are assigned. XDI identifiers for relational arcs are not required to be unique in a context. All literal arcs have the same XDI identifier -- the ampersand symbol. As defined in the XDI ABNF, XDI identifiers may be native references or external references. External references may be to locally unique identifiers or to globally unique URIs.

XDI address: The unique address, expressed as a string, of any node in any XDI graph. The address is composed of the XDI identifiers of every contextual arc that must be traversed to reach that node in the XDI semantic tree. Note that, through the use of XDI equivalence relations (i.e., $ref and $rep), more than one XDI address may ultimately resolve to the same XDI graph node.

"REAL": An acronym for "Root-Entity-Attribute-Literal" -- the order in which the four basic node types may appear in an XDI graph.

Common root node: The starting node of all XDI graphs and the only node common to all XDI graphs. The common root node may contain other peer root nodes and inner root nodes; this is how the XDI graph model supports heterarchy.

Peer root node: A node in an XDI graph representing the common root node of a separate XDI graph. Peer root nodes are how the XDI graph model represents heterarchical peer-to-peer relationships of XDI graphs within a rooted tree. A node that appears as a peer root node in one XDI graph is the common root node in its own XDI graph. Each peer root node contains its own peer graph which must be logically consistent with the peer graph contained by any other peer root node, i.e., each peer graph is a subset of the XDI global logical common graph.

Inner root node: A node in an XDI graph representing the root of another XDI graph whose subjects are all objects of the same XDI relation. Each inner root node contains its own unique inner graph which can only be understood in the context of the relational statement that uniquely defines it. Therefore inner graphs do not have to be logically consistent with the XDI global logical common graph.

Common graph: The subset of an XDI graph that begins with the common root node but does not include any peer root nodes. The common graph contains only inner root, entity, attribute, and literal nodes.

Peer graph: The graph contained by a peer root node. A peer graph may contain other peer root nodes or inner root nodes.

Inner graph: The graph contained by an inner root node. An inner graph may contain other inner root nodes.

Absolute address: An XDI address that begins with the common root node, a peer root node, or an inner root node. Examples: =example<#work><#email>, (+example)=example<#work><#email>, (=example/#example)+example$contract$do. An absolute address must be either a common address, peer-rooted address, or inner-rooted address.

Common address: An absolute XDI address that is relative to the common root node. Example: =example<#work><#email>.

Peer-rooted address: An absolute XDI address that is relative to a peer root node. Example: (+example)=example<#work><#email>.

Inner-rooted address: An absolute XDI address that is relative to inner root node. Example: (+example/#example)=example<#work><#email>.

Root-relative address: An XDI address that is relative to any type of root node. Syntactically, a root-relative address is indistinguishable from a common address, however the term is used for precision in the XDI specifications when an address may be relative to any kind of root node.

Relative address: An XDI address that begins with one or more variables indicating the specific type(s) of nodes the address may be relative to. Example: {=}<#work><#email>, {+}<#incorporation><$date>, {}$do$if.

XDI Binding

Transport binding:



HTTP requester:

HTTP responder:

HTTP 1.1 requester:

XDI request:

XDI processor:

XDI Messaging

Target graph: An XDI graph exposed at an XDI endpoint, which can be the target of a request message envelope. The operations in the request message(s) are applied to the target graph and may alter it and/or produce a synchronous response or asynchronous response.

Message envelope: An XDI graph transmitted using one of the XDI transport bindings. The message envelope contains a [$msg] collection with one or more message(s). A message envelope may be a request message envelope sent from a requester to a responder, or it may be a response message envelope sent from a responder to a requester.

Message: A member of a [$msg] collection in the message envelope. The message contains one or more operations. It may be a request message or a response message.

Operation: A relational statement ($get, $set, $del, $add, $mod, $do) on a $do context node on a message, specifying the operation(s) to be applied to a target graph.

Synchronous response: An XDI graph containing the XDI statements which are the result of the operations in a request message envelope.

Asynchronous response: A response message envelope which is the response to the request message envelope. It contains the XDI statements which are the result of the operations in the request message envelope.

XDI Policy

XDI policy: The rules and practices by which XDI authorities protect information graphs from unauthorized access operations, or unauthorized usage.

Authorizing authority (AA): The entity or organization controlling an XDI graph to which it may authorize access.

Requesting authority (RA): An entity or organization requesting access to an AA’s graph.

Operational policies: Control access to the graph. They can be specified in XDI link contracts or XDI messages and optionally make use of conditional policy expressions.

Usage policies: Specify RA’s permissions to use data from the AA’s graph once the data is accessed. In many cases the obligation to honor a usage policy must be specified in a legal (or other) agreement for it to be effective.

Conditional policy expressions: Boolean reserved words and patterns for use in XDI policies.

Other policy variables: Time and other variables may be used in policy expressions.

Link contract: An XDI subgraph used for access control, or authorization between an AA and an RA. It is a machine-readable agreement describing data shared and permissions granted by one XDI authority to another. A link contract describes both the policy that must be satisfied by an XDI message to be accepted and the permissions granted to the RA if those conditions are met. Link contracts may be used to apply and enforce any type of policy over shared data and messages, including security, privacy, re-sharing, synchronization, and termination.

XDI Connections

Link contract instantiation: The process of creating a link contract instance from a template, and all preceding steps for the XDI authorities to agree on one XDI connection.

XDI connection: A uni-directional component of a relationship between two or more XDI authorities, manifested by a link contract instance. XDI connection is essentially synonymous with the term link contract.

XDI connection request: An XDI message triggering link contract instantiation, providing a template and requesting a link contract instance.

XDI connection invitation: The inverse of the connection request, in which an authority invites another to send it a connection request. In the connection invitation, the XDI authority may publishes a template it is willing to accept. If accepted, the connection invitation will result in a connection request.

XDI peer relationship: A set of related connections (TBD).

XDI connection manager: Software that end users use to create connections.

XDI service endpoint: The software controlling a peer graph, and containing an authorization manager service for link contract instantiation.

XDI user agent: The component used by a person to interact with web sites or other artifacts publishing XDI connection requests and connection invitations, e.g. connection manager UI or purpose-built API.

Glossary (last edited 2015-03-23 03:45:07 by drummond-xns)