3.1 Abstract Property Definitions
Message addressing properties collectively augment a message with the following abstract properties to support one way, request reply, and other interaction pattern:

[destination] : IRI (1..1) 
An absolute IRI representing the address of the intended receiver of this message.

[source endpoint] : endpoint reference (0..1) 
Reference to the endpoint from which the message originated.

[reply endpoint] : endpoint reference (0..1) 
An endpoint reference for the intended receiver for replies to this message.

[fault endpoint] : endpoint reference (0..1) 
An endpoint reference for the intended receiver for faults related to this message.

[action] : IRI (1..1) 
An absolute IRI that uniquely identifies the semantics implied by this message.

It is RECOMMENDED that the value of the [action] property is an IRI identifying an input, output, or fault message within a WSDL interface. An action may be explicitly or implicitly associated with the corresponding WSDL definition. Web Services Addressing 1.0 - WSDL Binding[WS-Addressing-WSDL] describes the mechanisms of association.

[message id] : IRI (0..1) 
An absolute IRI that uniquely identifies this message in time and space. No two messages with a distinct application intent may share a [message id] property. A message MAY be retransmitted for any reason including communications failure and MAY use the same [message id] property. The value of this property is an opaque IRI whose interpretation beyond equivalence is not defined in this specification.

[relationship] : (IRI, IRI) (0..unbounded) 
A pair of values that indicate how this message relates to another message. The type of the relationship is identified by an absolute IRI. The related message is identified by an absolute IRI that corresponds to the related message's [message id] property. The message identifier IRI may refer to a specific message, or be the following well-known URI that means "unspecified message": "http://www.w3.org/@@@@/@@/addressing/id/unspecified" 

This specification has one predefined relationship type as shown in Table 3-1.

Table 3-1. Predefined [relationship] values URI Description  
"http://www.w3.org/@@@@/@@/addressing/reply"  Indicates that this is a reply to the message identified by the [message id] IRI. 

[reference parameters] : xs:any (0..unbounded). 
Corresponds to the value of the [reference parameters] property of the endpoint reference to which the message is addressed.

The [destination] and [action] properties indicate the target processing location and the verb or intent of the message respectively. The values of these properties can be used to facilitate the dispatch of incoming messages.

Due to the range of network technologies currently in wide-spread use (e.g., NAT, DHCP, firewalls), many deployments cannot assign a meaningful global IRI to a given endpoint. To allow these "anonymous" endpoints to send and receive messages, WS-Addressing defines the following well-known URI for use by endpoints that cannot have a stable, resolvable IRI: "http://www.w3.org/@@@@/@@/addressing/address/anonymous" 

Requests whose [reply endpoint], [source endpoint] and/or [fault endpoint] use this address MUST provide some out-of-band mechanism for delivering replies or faults (e.g. returning the reply on the same transport connection).