The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 .

This specification uses two namespace prefixes throughout; they are listed in . Note that the choice of any namespace prefix is arbitrary and not semantically significant (see ).

Namespace names of the general form http://example.org/... and http://example.com/... represent application or context-dependent URIs .

All parts of this specification are normative, with the exception of examples and sections explicitly marked as "Non-Normative".

A SOAP message is specified as an XML Information Set . While all SOAP message examples in this document are shown using XML 1.0 syntax, other representations MAY be used to transmit SOAP messages between nodes (see ).

Some of the information items defined by this document are identified using XML namespace names (see ). In particular, this document defines the following namespace names:

Normative XML Schema , documents for these namespace names can be found by dereferencing the namespace names above.

SOAP does not require that XML Schema processing (assessment or validation) be performed to establish the correctness or 'schema implied' values of element and attribute information items defined by this specification. The values associated with element and attribute information items defined in this specification MUST be carried explicitly in the transmitted SOAP message except where stated otherwise (see ).

SOAP attribute information items have types described by XML Schema: Datatypes . Unless otherwise stated, all lexical forms are supported for each such attribute, and lexical forms representing the same value in the XML Schema value space are considered equivalent for purposes of SOAP processing, e.g. the boolean lexical forms 1 and true are interchangeable. For brevity, text in this specification refers only to one lexical form for each value, e.g. "if the value of the mustUnderstand attribute information item is 'true'".

Specifications for the processing of application-defined data carried in a SOAP message but not defined by this specification MAY call for additional validation of the SOAP message in conjunction with application-level processing. In such cases, the choice of schema language and/or validation technology is at the discretion of the application.

SOAP uses XML Base for determining a base URI for relative URI references used as values in information items defined by this specification (see ).

The media type "application/soap+xml" (IETF registration pending ) SHOULD be used for XML 1.0 serializations of the SOAP message infoset.

The following example shows a sample notification message expressed in SOAP. The message contains two pieces of application-defined data not defined by this specification: a SOAP header block with a local name of alertcontrol and a body element with a local name of alert. In general, SOAP header blocks contain information which might be of use to intermediaries as well as the ultimate destination of the message. In this example an intermediary might prioritize the delivery of the message based on the priority and expiration information in the SOAP header block. The body contains the actual message payload, in this case the alert message.

This section describes the terms and concepts introduced in Part 1 of the SOAP specification (this document).

A SOAP node can be the initial SOAP sender, an ultimate SOAP receiver, or a SOAP intermediary. An intermediary is both a SOAP sender and a SOAP receiver.

A SOAP node receiving a SOAP message MUST perform processing according to the SOAP processing model as described in this section and in the remainder of this specification.

A SOAP node MUST be identified by a URI.

In processing a SOAP message, a SOAP node is said to act in one or more SOAP roles, each of which is identified by a URI known as the SOAP role name. The roles assumed by a node MUST be invariant during the processing of an individual SOAP message. This specification deals only with the processing of individual SOAP messages. No statement is made regarding the possibility that a given SOAP node might or might not act in varying roles when processing more than one SOAP message.

This specification defines the following SOAP roles:

In addition to those described above, other roles MAY be defined as necessary to meet the needs of SOAP applications.

While the purpose of a SOAP role name is to identify a SOAP node or nodes, there are no routing or message exchange semantics associated with the SOAP role name. For example, SOAP roles MAY be named with a URI useable to route SOAP messages to an appropriate SOAP node. Conversely, it is also appropriate to use SOAP roles with names that are related more indirectly to message routing (e.g. http://example.org/banking/anyAccountMgr) or which are unrelated to routing (e.g. a URI meant to identify "all cache management software"; such a header might be used, for example, to carry an indication to any concerned software that the containing SOAP message is idempotent, and can safely be cached and replayed).

With the exception of the three SOAP roles defined above, this specification does not prescribe the criteria by which a given node determines the (possibly empty) set of roles in which it acts on a given message. For example, implementations can base this determination on factors including, but not limited to: hard coded choices in the implementation, information provided by the underlying protocol binding (e.g. the URI to which the message was physically delivered), or configuration information provided by users during system installation.

A SOAP header block MAY carry a role attribute information item (see ) that is used to target the header block at SOAP nodes operating in the specified role. This specification refers to the value of the SOAP role attribute as the SOAP role for the corresponding SOAP header block.

A SOAP header block is said to be targeted at a SOAP node if the SOAP role for the header block is the name of a role in which the SOAP node operates.

SOAP header blocks targeted at the special role http://www.w3.org/2002/06/soap-envelope/role/none are carried with the message to the ultimate SOAP receiver(s), but are never formally processed. Such SOAP header blocks MAY carry data that is required for processing of other header blocks.

It is likely that specifications for a wide variety of header functions will be developed over time (see ), and that some SOAP nodes might include the software necessary to implement one or more such extensions. A SOAP header block is said to be understood by a SOAP node if the software at that SOAP node has been written to fully conform to and implement the semantics conveyed by the combination of local name and namespace name of the outer-most element information item of that header block.

SOAP header blocks MAY carry mustUnderstand attribute information items (see ). When the value of such an attribute information item is true, the SOAP block is said to be mandatory.

Mandatory SOAP header blocks are presumed to somehow modify the semantics of other headers or body elements. Therefore, for every mandatory SOAP header block targeted to a node, that node MUST either process the header block or not process the SOAP message at all, and instead generate a fault (see and ). Tagging SOAP header blocks as mandatory thus assures that such modifications will not be silently (and, presumably, erroneously) ignored by a SOAP node to which the header block is targeted.

The mustUnderstand attribute information item is not intended as a mechanism for detecting errors in routing, misidentification of nodes, failure of a node to serve in its intended role(s), etc. Any of these conditions can result in a failure to even attempt processing of a given SOAP header block from a SOAP envelope. This specification therefore does not require any fault to be generated based on the presence or value of the mustUnderstand attribute information item on a SOAP header block not targeted at the current processing node. In particular, it is not an error for an ultimate SOAP receiver to receive a message containing a mandatory header block that is targeted at a role other than the ones assumed by the ultimate SOAP receiver. This is the case, for example, when a header block has survived erronously due to a routing or targeting error at a preceeding intermediairy.

An ultimate SOAP receiver MUST correctly process the immediate children of the SOAP body (see ). However, with the exception of SOAP faults (see ), Part 1 of this specification (this document) mandates no particular structure or interpretation of these elements, and provides no standard means for specifying the processing to be done.

This section sets out the rules by which SOAP messages are processed. Unless otherwise stated, processing MUST be semantically equivalent to performing the following steps separately, and in the order given. Note however that nothing in this specification prevents the use of optimistic concurrency, roll back, or other techniques that might provide increased flexibility in processing order provided all generated SOAP messages, SOAP faults and application-level side effects are equivalent to those that would be obtained by direct implementation of the following rules in the order shown below.

In all cases where a SOAP header block is processed, the SOAP node MUST understand the SOAP header block and MUST do such processing in a manner fully conformant with the specification for that header block. An ultimate SOAP receiver MUST process the SOAP body, in a manner consistent with .

Failure is indicated by the generation of a fault (see ). SOAP message processing MAY result in the generation of at-most one fault. Header-related faults other than those related to understanding header blocks (see ) MUST conform to the specification for the corresponding SOAP header block.

SOAP nodes MAY make reference to any information in the SOAP envelope when processing a SOAP body or SOAP header block. For example, a caching function can cache the entire SOAP message, if desired.

The processing of one or more SOAP header blocks MAY control or determine the order of processing for other SOAP header blocks and/or the SOAP body. For example, one could create a SOAP header block to force processing of other SOAP header blocks in lexical order. In the absence of such a controlling SOAP header block, the order of header and body processing is at the discretion of the SOAP node. Header blocks MAY be processed in arbitrary order. Header block processing MAY precede, MAY be interleaved with, or MAY follow processing of the body. For example, processing of a "begin transaction" header block would typically precede body processing, a "logging" function might run concurrently with body processing and a "commit transaction" header might be honored following completion of all other work.

As mentioned earlier in this section, it is assumed that a SOAP message originates at an initial SOAP sender and is sent to an ultimate SOAP receiver via zero or more SOAP intermediaries. While SOAP does not itself define any routing or forwarding semantics, it is anticipated that such functionality can be described as one or more features and then expressed as SOAP extensions or as part of the underlying protocol binding (see and ). The purpose of this section is to describe how message forwarding interacts with the SOAP distributed processing model.

SOAP defines two different types of intermediaries: forwarding intermediaries and active intermediaries. These two types of intermediary are described below.

The version of a SOAP message is identified by the qualified name of the child element information item of the document information item. A SOAP Version 1.2 message has a child element information item of the document information item with a local name of Envelope and a namespace name of http://www.w3.org/2002/06/soap-envelope (see ).

A SOAP node determines whether it supports the version of a SOAP message on a per message basis. In this context "support" means understanding the semantics of that version of a SOAP envelope. The versioning model is directed only at the Envelope element information item. It does NOT address versioning of SOAP header blocks, encodings, protocol bindings, or anything else.

A SOAP node MAY support multiple envelope versions. However, when processing a message, a SOAP node MUST use the semantics defined by the version of that message.

If a SOAP node receives a message whose version is not supported it MUST generate a fault (see ) with a Value of Code set to env:VersionMismatch. Any other malformation of the message construct MUST result in the generation of a fault with a Value of Code set to env:Sender.

Appendix defines a mechanism for transitioning from SOAP/1.1 to SOAP Version 1.2 using the Upgrade element information item (see ).

For the purpose of this specification, the term "feature" is used to identify an abstract piece of functionality typically associated with the exchange of messages between communicating SOAP nodes. Although SOAP poses no constraints on the potential scope of such features, example features include "reliability", "security", "correlation", and "routing". In addition, the communication might require a variety of message exchange patterns (MEPs) such as one-way messages, request/response interactions, and peer-to-peer conversations. MEPs are considered to be a type of feature, and unless otherwise stated, references in this specification to the term "feature" apply also to MEPs.

The SOAP extensibility model provides two mechanisms through which features can be expressed: the SOAP Processing Model and the SOAP Protocol Binding Framework (see and ). The former describes the behavior of a single SOAP node with respect to the processing of an individual message. The latter mediates the act of sending and receiving SOAP messages by a SOAP node via an underlying protocol.

The SOAP Processing Model enables SOAP nodes that include the mechanisms necessary to implement one or more features to express such features within the SOAP envelope as header blocks (see ). Such header blocks can be intended for any SOAP node or nodes along a SOAP message path (see ). A feature expressed as SOAP headers is known as a SOAP module, and each module is specified according to the rules in .

In contrast, a SOAP protocol binding operates between two adjacent SOAP nodes along a SOAP message path. There is no requirement that the same underlying protocol is used for all hops along a SOAP message path. In some cases, underlying protocols are equipped, either directly or through extension, with mechanisms for providing certain features. The SOAP Protocol Binding Framework provides a scheme for describing these features and how they relate to SOAP nodes through a binding specification (see ).

Certain features might require end-to-end as opposed to hop-to-hop processing semantics. While the SOAP Protocol Binding Framework provides for the possibility that such features could be expressed outside the SOAP envelope, it does not define a specific architecture for the processing or error handling of these externally expressed features by a SOAP intermediary. A binding specification that expresses such features external to the SOAP envelope needs to define its own processing rules to which a SOAP node is expected to conform (for example, describing what information is passed along with the SOAP message as it leaves the intermediary). It is recommended that, where practical, end-to-end features be expressed as SOAP header blocks, so that the rules defined by the SOAP Processing Model can be employed.

A SOAP module is a feature which is expressed as SOAP headers.

A module specification follows the following rules. It:

An MEP is a template that establishes a pattern for the exchange of messages between SOAP nodes. An MEP MAY be supported by one or more underlying protocol binding instances.

This section is a logical description of the operation of a MEP. It is not intended to describe a real implementation or to imply that a real implementation needs to be similarly structured.

In general the definition of a message exchange pattern:

Underlying protocol binding specifications can declare their support for one or more named MEPs.

The goals of the binding framework are:

Two or more bindings can offer a given optional feature, such as reliable delivery, using different means. One binding might exploit an underlying protocol that directly facilitates the feature (e.g., the protocol is reliable), and the other binding might provide the necessary logic itself (e.g., reliability is achieved via logging and retransmission). In such cases, the feature can be made available to applications in a consistent manner, regardless of which binding is used.

The creation, transmission, and processing of a SOAP message, possibly through one or more intermediaries, is specified in terms of a distributed state machine. The state consists of information known to a SOAP node at a given point in time, including but not limited to the contents of messages being assembled for transmission or received for processing. The state at each node can be updated either by local processing, or by information received from an adjacent node.

Section of this specification describes the processing that is common to all SOAP nodes when receiving a message. The purpose of a binding specification is to augment those core SOAP rules with additional processing that is particular to the binding, and to specify the manner in which the underlying protocol is used to transmit information between adjacent nodes in the message path.

The distributed state machine that manages the transmission of a given SOAP message through its message path is the combination of the core SOAP processing (see ) operating at each node, in conjunction with the binding specifications connecting each pair of nodes. A binding specification MUST enable one or more MEP.

In cases where multiple features are supported by a binding specification the specifications for those features MUST provide any information necessary for their successful use in combination; this binding framework does not provide any explicit mechanism for ensuring such compatibility of multiple features.

The binding framework provides no fixed means of naming or typing the information comprising the state at a given node. Individual feature and binding specifications are free to adopt their own conventions for specifying state. Note, however, that consistency across bindings and features is likely to be enhanced in situations where multiple feature specifications adopt consistent conventions for representing state. For example, multiple features might benefit from a consistent specification for an authentication credential, a transaction ID, etc. The HTTP binding in SOAP Part 2 illustrates one such convention.

As described in , each SOAP message is modeled as an XML Infoset that consists of a document information item with exactly one child: the envelope element information item. Therefore, the minimum responsibility of a binding in transmitting a message is to specify the means by which the SOAP XML Infoset is transferred to and reconstituted by the binding at the receiving SOAP node and to specify the manner in which the transmission of the envelope is effected using the facilities of the underlying protocol.

The binding framework does NOT require that every binding use the XML 1.0 serialization as the "on the wire" representation of the Infoset; compressed, encrypted, fragmented representations and so on can be used if appropriate. A binding, if using XML 1.0 serialization of the infoset, MAY mandate that a particular character encoding or set of encodings be used.

Bindings MAY provide for streaming when processing messages. That is, SOAP nodes MAY begin processing a received SOAP message as soon as the necessary information is available. SOAP processing is specified in terms of Envelope XML infosets (see ). Although streaming SOAP receivers will acquire such Infosets incrementally, SOAP processing MUST yield results identical to those that would have been achieved if the entire SOAP envelope were available prior to the start of processing. For example, as provided in , identification of targeted header blocks, and checking of all mustUnderstand attributes is to be done before successful processing can proceed. Depending on the representation used for the Infoset, and the order in which it is transmitted, this rule might limit the degree to which streaming can be achieved.

Bindings MAY depend on state that is modeled as being outside of the SOAP XML Infoset (e.g. retry counts), and MAY transmit such information to adjacent nodes. For example, some bindings take a message delivery address (typically a URI) that is not within the envelope.

The Envelope element information item has:

The SOAP Header element information item provides a mechanism for extending a SOAP message in a decentralized and modular way (see and ).

The Header element information item has:

Each child element information item of the SOAP Header is called a SOAP header block.

A SOAP body provides a mechanism for transmitting information to an ultimate SOAP receiver (see ).

The Body element information item has:

A SOAP fault is used to carry error information within a SOAP message.

The Fault element information item has:

To be recognized as carrying SOAP error information, a SOAP message MUST contain a single SOAP Fault element information item as the only child of the SOAP Body.

When generating a fault, SOAP senders MUST NOT include additional element information items in the SOAP Body. A message whose Body contains a Fault plus additional element information items has no SOAP-defined semantics.

A SOAP Fault element information item MAY appear within a SOAP header block, or as a descendant of a child element information item of the SOAP Body; in such cases, the element has no SOAP-defined semantics.

SOAP can carry application-defined data as SOAP header blocks or as SOAP body contents. Processing a SOAP header block might include dealing with side effects such as state changes, logging of information, or the generation of additional messages. It is strongly recommended that, for any deployment scenario, only carefully specified header blocks with well understood security implications of any side effects be processed by a SOAP node.

Similarly, processing a SOAP body might imply the occurrence of side affects that could, if not properly understood, have severe consequences for the receiving SOAP node. It is strongly recommended that only well-defined body contents with known security implications be processed.

Security considerations, however, are not just limited to recognizing the immediate child elements of the SOAP header and the SOAP body. Implementors need to pay special attention to the security implications of all data carried within a SOAP message that can cause the remote execution of any actions in the receiver's environment. This includes not only data expressed in XML infoset but data that might be encoded as binary data or carried as parameters, for example URI query strings. Before accepting data of any type, an application ought to be aware of the particular security implications associated with that data within the context it is being used.

SOAP implementors need to be careful to ensure that if processing of the various parts of a SOAP message is provided through modular software architecture, that each module is aware of the overall security context. For example, a SOAP body ought not to be processed without knowing the context in which it was received.

SOAP inherently provides a distributed processing model that might involve a SOAP message passing through multiple SOAP nodes (see ). SOAP intermediaries are by definition men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Security breaches on systems that run SOAP intermediaries can result in serious security and privacy problems. A compromised SOAP intermediary, or an intermediary implemented or configured without regard to security and privacy considerations, might be used in the commission of a wide range of potential attacks.

In analyzing the security implications of potential SOAP related security problems, it is important to realize that the scope of security mechanisms provided by the underlying protocol might not be the same scope as the whole message path of the SOAP message. There is no requirement in SOAP that all hops between participating SOAP nodes use the same underlying protocol and even if this were the case, the very use of SOAP intermediaries is likely to reach beyond the scope of transport-level security.

The effects on security of not implementing a MUST or SHOULD, or doing something the specification says MUST NOT or SHOULD NOT be done can be very subtle. Binding specification authors ought to describe, in detail, the security implications of not following recommendations or requirements as most implementors will not have had the benefit of the experience and discussion that produced the specification (see ).

In addition, a binding specification might not address or provide countermeasures for all aspects of the inherent security risks. The binding specification authors ought to identify any such risks as might remain and indicate where further countermeasures would be needed above and beyond those provided for in the binding specification.

Authors of binding specifications need to be aware that SOAP extension modules expressed as SOAP header blocks could affect the underlying protocol in unforeseen ways. A SOAP message carried over a particular protocol binding might result in seemingly conflicting features. An example of this is a SOAP message carried over HTTP, using the HTTP basic authentication mechanism in combination with a SOAP based authentication mechanism. It is strongly recommended that a binding specification describes any such interactions between the extensions and the underlying protocols.