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Subject: RE: SOAP Proposal Documents
Thanks Robert, I originally had the ErrorList within SOAP-ENV:Fault and after discussions, we decided to pull it out. This was primarily due to the limitation on SOAP Header errors. We can put SOAP Body errors in SOAP Fault but there is a limitation on SOAP Header errors... that requires another error list external to SOAP Fault. (see SOAP 1.1 section 4.4 sub-section "detail"). The discussion was to keep the ebXML errors together rather than mix-and-match with two lists. This limits the changes to our document. We would still support SOAP specific errors within SOAP Fault. Did the discussion change afterwards to put it back? I can certainly change it back. If it goes back, does there need to be another error list in the Header? IMO it was better (less work for the editors) to keep the errors together. Regards, David Fischer Drummond Group 817-371-8422 -----Original Message----- From: Robert Fox [mailto:firstname.lastname@example.org] Sent: Tuesday, February 20, 2001 4:39 PM To: 'email@example.com'; ebXML Transport (E-mail) Subject: RE: SOAP Proposal Documents 1) The PPT diagram may need to be changed to show the eb:ErrorList element inside the SOAP-FAULT as discussed 2) re: contribution credits in the document: Robert Fox - Softshare Thanx! Great week gang! ~Rob -----Original Message----- From: David Fischer [mailto:firstname.lastname@example.org] Sent: Tuesday, February 20, 2001 2:31 PM To: ebXML Transport (E-mail) Subject: SOAP Proposal Documents Welcome home from Vancouver, These are the three SOAP related documents we used on the overhead in Vancouver. It is my understanding there is some problem with the ebXML/SOAP press release scheduled for today. It may not go out yet. Please do not distribute these documents too far. On the PPT, the right picture is the old structure and the left is the new proposed SOAP structure. Also, Rik asked if any document contributor does not see their name on the 0.93 version, please reply with name and company so we may correct that oversight. Regards, David Fischer Drummond Group 817-371-8422Title: Simple Object Access Protocol (SOAP) 1.1
Simple Object Access Protocol (SOAP) 1.1
W3C Note 08 May 2000
SOAP is a lightweight protocol for exchange of information in a decentralized, distributed environment. It is an XML based protocol that consists of three parts: an envelope that defines a framework for describing what is in a message and how to process it, a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing remote procedure calls and responses. SOAP can potentially be used in combination with a variety of other protocols; however, the only bindings defined in this document describe how to use SOAP in combination with HTTP and HTTP Extension Framework.
This document is a submission to the World Wide Web Consortium (see Submission Request, W3C Staff Comment) to propose the formation of a working group in the area of XML-based protocols. Comments are welcome to the authors but you are encouraged to share your views on the W3C's public mailing list mailto:email@example.com (see archives).
This document is a NOTE made available by the W3C for discussion only. Publication of this Note by W3C indicates no endorsement by W3C or the W3C Team, or any W3C Members. W3C has had no editorial control over the preparation of this Note. This document is a work in progress and may be updated, replaced, or rendered obsolete by other documents at any time.
A list of current W3C technical documents can be found at the Technical Reports page.
SOAP provides a simple and lightweight mechanism for exchanging structured and typed information between peers in a decentralized, distributed environment using XML. SOAP does not itself define any application semantics such as a programming model or implementation specific semantics; rather it defines a simple mechanism for expressing application semantics by providing a modular packaging model and encoding mechanisms for encoding data within modules. This allows SOAP to be used in a large variety of systems ranging from messaging systems to RPC.
SOAP consists of three parts:
Although these parts are described together as part of SOAP, they are functionally orthogonal. In particular, the envelope and the encoding rules are defined in different namespaces in order to promote simplicity through modularity.
In addition to the SOAP envelope, the SOAP encoding rules and the SOAP RPC conventions, this specification defines two protocol bindings that describe how a SOAP message can be carried in HTTP  messages either with or without the HTTP Extension Framework .
A major design goal for SOAP is simplicity and extensibility. This means that there are several features from traditional messaging systems and distributed object systems that are not part of the core SOAP specification. Such features include
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 .
The namespace prefixes "SOAP-ENV" and "SOAP-ENC" used in this document are associated with the SOAP namespaces "http://schemas.xmlsoap.org/soap/envelope/" and "http://schemas.xmlsoap.org/soap/encoding/" respectively.
Throughout this document, the namespace prefix "xsi" is assumed to be associated with the URI "http://www.w3.org/1999/XMLSchema-instance" which is defined in the XML Schemas specification . Similarly, the namespace prefix "xsd" is assumed to be associated with the URI "http://www.w3.org/1999/XMLSchema" which is defined in . The namespace prefix "tns" is used to indicate whatever is the target namespace of the current document. All other namespace prefixes are samples only.
Namespace URIs of the general form "some-URI" represent some application-dependent or context-dependent URI .
This specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2616  for certain constructs.
In this example, a GetLastTradePrice SOAP request is sent to a StockQuote service. The request takes a string parameter, ticker symbol, and returns a float in the SOAP response. The SOAP Envelope element is the top element of the XML document representing the SOAP message. XML namespaces are used to disambiguate SOAP identifiers from application specific identifiers. The example illustrates the HTTP bindings defined in section 6. It is worth noting that the rules governing XML payload format in SOAP are entirely independent of the fact that the payload is carried in HTTP.
More examples are available in Appendix A.
Example 1 SOAP Message Embedded in HTTP Request
POST /StockQuote HTTP/1.1
Following is the response message containing the HTTP message with the SOAP message as the payload:
Example 2 SOAP Message Embedded in HTTP Response
HTTP/1.1 200 OK
SOAP messages are fundamentally one-way transmissions from a sender to a receiver, but as illustrated above, SOAP messages are often combined to implement patterns such as request/response.
SOAP implementations can be optimized to exploit the unique characteristics of particular network systems. For example, the HTTP binding described in section 6 provides for SOAP response messages to be delivered as HTTP responses, using the same connection as the inbound request.
Regardless of the protocol to which SOAP is bound, messages are routed along a so-called "message path", which allows for processing at one or more intermediate nodes in addition to the ultimate destination.
A SOAP application receiving a SOAP message MUST process that message by performing the following actions in the order listed below:
Processing a message or a part of a message requires that the SOAP processor understands, among other things, the exchange pattern being used (one way, request/response, multicast, etc.), the role of the recipient in that pattern, the employment (if any) of RPC mechanisms such as the one documented in section 7, the representation or encoding of data, as well as other semantics necessary for correct processing.
While attributes such as the SOAP encodingStyle attribute (see section 4.1.1) can be used to describe certain aspects of a message, this specification does not mandate a particular means by which the recipient makes such determinations in general. For example, certain applications will understand that a particular <getStockPrice> element signals an RPC request using the conventions of section 7, while another application may infer that all traffic directed to it is encoded as one way messages.
All SOAP messages are encoded using XML (see  for more information on XML).
A SOAP application SHOULD include the proper SOAP namespace on all elements and attributes defined by SOAP in messages that it generates. A SOAP application MUST be able to process SOAP namespaces in messages that it receives. It MUST discard messages that have incorrect namespaces (see section 4.4) and it MAY process SOAP messages without SOAP namespaces as though they had the correct SOAP namespaces.
SOAP defines two namespaces (see  for more information on XML namespaces):
A SOAP message MUST NOT contain a Document Type Declaration. A SOAP message MUST NOT contain Processing Instructions. 
SOAP uses the local, unqualified "id" attribute of type "ID" to specify the unique identifier of an encoded element. SOAP uses the local, unqualified attribute "href" of type "uri-reference" to specify a reference to that value, in a manner conforming to the XML Specification , XML Schema Specification , and XML Linking Language Specification .
With the exception of the SOAP mustUnderstand attribute (see section 4.2.3) and the SOAP actor attribute (see section 4.2.2), it is generally permissible to have attributes and their values appear in XML instances or alternatively in schemas, with equal effect. That is, declaration in a DTD or schema with a default or fixed value is semantically equivalent to appearance in an instance.
A SOAP message is an XML document that consists of a mandatory SOAP envelope, an optional SOAP header, and a mandatory SOAP body. This XML document is referred to as a SOAP message for the rest of this specification. The namespace identifier for the elements and attributes defined in this section is "http://schemas.xmlsoap.org/soap/envelope/". A SOAP message contains the following:
The grammar rules are as follows:
The SOAP encodingStyle global attribute can be used to indicate the serialization rules used in a SOAP message. This attribute MAY appear on any element, and is scoped to that element's contents and all child elements not themselves containing such an attribute, much as an XML namespace declaration is scoped. There is no default encoding defined for a SOAP message.
The attribute value is an ordered list of one or more URIs identifying the serialization rule or rules that can be used to deserialize the SOAP message indicated in the order of most specific to least specific. Examples of values are
The serialization rules defined by SOAP in section 5 are identified by the URI "http://schemas.xmlsoap.org/soap/encoding/". Messages using this particular serialization SHOULD indicate this using the SOAP encodingStyle attribute. In addition, all URIs syntactically beginning with "http://schemas.xmlsoap.org/soap/encoding/" indicate conformance with the SOAP encoding rules defined in section 5 (though with potentially tighter rules added).
A value of the zero-length URI ("") explicitly indicates that no claims are made for the encoding style of contained elements. This can be used to turn off any claims from containing elements.
4.1.2 Envelope Versioning Model
SOAP does not define a traditional versioning model based on major and minor version numbers. A SOAP message MUST have an Envelope element associated with the "http://schemas.xmlsoap.org/soap/envelope/" namespace. If a message is received by a SOAP application in which the SOAP Envelope element is associated with a different namespace, the application MUST treat this as a version error and discard the message. If the message is received through a request/response protocol such as HTTP, the application MUST respond with a SOAP VersionMismatch faultcode message (see section 4.4) using the SOAP "http://schemas.xmlsoap.org/soap/envelope/" namespace.
SOAP provides a flexible mechanism for extending a message in a decentralized and modular way without prior knowledge between the communicating parties. Typical examples of extensions that can be implemented as header entries are authentication, transaction management, payment etc.
The Header element is encoded as the first immediate child element of the SOAP Envelope XML element. All immediate child elements of the Header element are called header entries.
The encoding rules for header entries are as follows:
The SOAP Header attributes defined in this section determine how a recipient of a SOAP message should process the message as described in section 2. A SOAP application generating a SOAP message SHOULD only use the SOAP Header attributes on immediate child elements of the SOAP Header element. The recipient of a SOAP message MUST ignore all SOAP Header attributes that are not applied to an immediate child element of the SOAP Header element.
An example is a header with an element identifier of "Transaction", a "mustUnderstand" value of "1", and a value of 5. This would be encoded as follows:
A SOAP message travels from the originator to the ultimate destination, potentially by passing through a set of SOAP intermediaries along the message path. A SOAP intermediary is an application that is capable of both receiving and forwarding SOAP messages. Both intermediaries as well as the ultimate destination are identified by a URI.
Not all parts of a SOAP message may be intended for the ultimate destination of the SOAP message but, instead, may be intended for one or more of the intermediaries on the message path. The role of a recipient of a header element is similar to that of accepting a contract in that it cannot be extended beyond the recipient. That is, a recipient receiving a header element MUST NOT forward that header element to the next application in the SOAP message path. The recipient MAY insert a similar header element but in that case, the contract is between that application and the recipient of that header element.
The SOAP actor global attribute can be used to indicate the recipient of a header element. The value of the SOAP actor attribute is a URI. The special URI "http://schemas.xmlsoap.org/soap/actor/next" indicates that the header element is intended for the very first SOAP application that processes the message. This is similar to the hop-by-hop scope model represented by the Connection header field in HTTP.
Omitting the SOAP actor attribute indicates that the recipient is the ultimate destination of the SOAP message.
The SOAP mustUnderstand global attribute can be used to indicate whether a header entry is mandatory or optional for the recipient to process. The recipient of a header entry is defined by the SOAP actor attribute (see section 4.2.2). The value of the mustUnderstand attribute is either "1" or "0". The absence of the SOAP mustUnderstand attribute is semantically equivalent to its presence with the value "0".
If a header element is tagged with a SOAP mustUnderstand attribute with a value of "1", the recipient of that header entry either MUST obey the semantics (as conveyed by the fully qualified name of the element) and process correctly to those semantics, or MUST fail processing the message (see section 4.4).
The SOAP mustUnderstand attribute allows for robust evolution. Elements tagged with the SOAP mustUnderstand attribute with a value of "1" MUST be presumed to somehow modify the semantics of their parent or peer elements. Tagging elements in this manner assures that this change in semantics will not be silently (and, presumably, erroneously) ignored by those who may not fully understand it.
The SOAP Body element provides a simple mechanism for exchanging mandatory information intended for the ultimate recipient of the message. Typical uses of the Body element include marshalling RPC calls and error reporting.
The Body element is encoded as an immediate child element of the SOAP Envelope XML element. If a Header element is present then the Body element MUST immediately follow the Header element, otherwise it MUST be the first immediate child element of the Envelope element.
All immediate child elements of the Body element are called body entries and each body entry is encoded as an independent element within the SOAP Body element.
The encoding rules for body entries are as follows:
SOAP defines one body entry, which is the Fault entry used for reporting errors (see section 4.4).
While the Header and Body are defined as independent elements, they are in fact related. The relationship between a body entry and a header entry is as follows: A body entry is semantically equivalent to a header entry intended for the default actor and with a SOAP mustUnderstand attribute with a value of "1". The default actor is indicated by not using the actor attribute (see section 4.2.2).
The SOAP Fault element is used to carry error and/or status information within a SOAP message. If present, the SOAP Fault element MUST appear as a body entry and MUST NOT appear more than once within a Body element.
The SOAP Fault element defines the following four subelements:
Other Fault subelements MAY be present, provided they are namespace-qualified.
The faultcode values defined in this section MUST be used in the faultcode element when describing faults defined by this specification. The namespace identifier for these faultcode values is "http://schemas.xmlsoap.org/soap/envelope/". Use of this space is recommended (but not required) in the specification of methods defined outside of the present specification.
The default SOAP faultcode values are defined in an extensible manner that allows for new SOAP faultcode values to be defined while maintaining backwards compatibility with existing faultcode values. The mechanism used is very similar to the 1xx, 2xx, 3xx etc basic status classes classes defined in HTTP (see  section 10). However, instead of integers, they are defined as XML qualified names (see  section 3). The character "." (dot) is used as a separator of faultcode values indicating that what is to the left of the dot is a more generic fault code value than the value to the right. Example
The set of faultcode values defined in this document is:
The SOAP encoding style is based on a simple type system that is a generalization of the common features found in type systems in programming languages, databases and semi-structured data. A type either is a simple (scalar) type or is a compound type constructed as a composite of several parts, each with a type. This is described in more detail below. This section defines rules for serialization of a graph of typed objects. It operates on two levels. First, given a schema in any notation consistent with the type system described, a schema for an XML grammar may be constructed. Second, given a type-system schema and a particular graph of values conforming to that schema, an XML instance may be constructed. In reverse, given an XML instance produced in accordance with these rules, and given also the original schema, a copy of the original value graph may be constructed.
The namespace identifier for the elements and attributes defined in this section is "http://schemas.xmlsoap.org/soap/encoding/". The encoding samples shown assume all namespace declarations are at a higher element level.
Use of the data model and encoding style described in this section is encouraged but not required; other data models and encodings can be used in conjunction with SOAP (see section 4.1.1).
XML allows very flexible encoding of data. SOAP defines a narrower set of rules for encoding. This section defines the encoding rules at a high level, and the next section describes the encoding rules for specific types when they require more detail. The encodings described in this section can be used in conjunction with the mapping of RPC calls and responses specified in Section 7.
To describe encoding, the following terminology is used:
Although it is possible to use the xsi:type attribute such that a graph of values is self-describing both in its structure and the types of its values, the serialization rules permit that the types of values MAY be determinate only by reference to a schema. Such schemas MAY be in the notation described by "XML Schema Part 1: Structures"  and "XML Schema Part 2: Datatypes"  or MAY be in any other notation. Note also that, while the serialization rules apply to compound types other than arrays and structs, many schemas will contain only struct and array types.
The rules for serialization are as follows:
Note that rule 2 allows independent elements and also elements representing the members of arrays to have names which are not identical to the type of the contained value.
For simple types, SOAP adopts all the types found in the section "Built-in datatypes" of the "XML Schema Part 2: Datatypes" Specification , both the value and lexical spaces. Examples include:
The datatypes declared in the XML Schema specification may be used directly in element schemas. Types derived from these may also be used. An example of a schema fragment and corresponding instance data with elements of these types is:
<element name="age" type="int"/>
All simple values MUST be encoded as the content of elements whose type is either defined in "XML Schema Part 2: Datatypes" Specification , or is based on a type found there by using the mechanisms provided in the XML Schema specification.
If a simple value is encoded as an independent element or member of a heterogenous array it is convenient to have an element declaration corresponding to the datatype. Because the "XML Schema Part 2: Datatypes" Specification  includes type definitions but does not include corresponding element declarations, the SOAP-ENC schema and namespace declares an element for every simple datatype. These MAY be used.
The datatype "string" is defined in "XML Schema Part 2: Datatypes" Specification . Note that this is not identical to the type called "string" in many database or programming languages, and in particular may forbid some characters those languages would permit. (Those values must be represented by using some datatype other than xsd:string.)
A string MAY be encoded as a single-reference or a multi-reference value.
The containing element of the string value MAY have an "id" attribute. Additional accessor elements MAY then have matching "href" attributes.
For example, two accessors to the same string could appear, as follows:
However, if the fact that both accessors reference the same instance of the string (or subtype of string) is immaterial, they may be encoded as two single-reference values as follows:
Schema fragments for these examples could appear similar to the following:
(In this example, the type SOAP-ENC:string is used as the element's type as a convenient way to declare an element whose datatype is "xsd:string" and which also allows an "id" and "href" attribute. See the SOAP Encoding schema for the exact definition. Schemas MAY use these declarations from the SOAP Encoding schema but are not required to.)
The "XML Schema Part 2: Datatypes" Specification  defines a mechanism called "enumeration." The SOAP data model adopts this mechanism directly. However, because programming and other languages often define enumeration somewhat differently, we spell-out the concept in more detail here and describe how a value that is a member of an enumerated list of possible values is to be encoded. Specifically, it is encoded as the name of the value.
"Enumeration" as a concept indicates a set of distinct names. A specific enumeration is a specific list of distinct values appropriate to the base type. For example the set of color names ("Green", "Blue", "Brown") could be defined as an enumeration based on the string built-in type. The values ("1", "3", "5") are a possible enumeration based on integer, and so on. "XML Schema Part 2: Datatypes"  supports enumerations for all of the simple types except for boolean. The language of "XML Schema Part 1: Structures" Specification  can be used to define enumeration types. If a schema is generated from another notation in which no specific base type is applicable, use "string". In the following schema example "EyeColor" is defined as a string with the possible values of "Green", "Blue", or "Brown" enumerated, and instance data is shown accordingly.
An array of bytes MAY be encoded as a single-reference or a multi-reference value. The rules for an array of bytes are similar to those for a string.
In particular, the containing element of the array of bytes value MAY have an "id" attribute. Additional accessor elements MAY then have matching "href" attributes.
The recommended representation of an opaque array of bytes is the 'base64' encoding defined in XML Schemas , which uses the base64 encoding algorithm defined in 2045 . However, the line length restrictions that normally apply to base64 data in MIME do not apply in SOAP. A "SOAP-ENC:base64" subtype is supplied for use with SOAP.
Many languages allow accessors that can polymorphically access values of several types, each type being available at run time. A polymorphic accessor instance MUST contain an "xsi:type" attribute that describes the type of the actual value.
For example, a polymorphic accessor named "cost" with a value of type "xsd:float" would be encoded as follows:
as contrasted with a cost accessor whose value's type is invariant, as follows:
SOAP defines types corresponding to the following structural patterns often found in programming languages:
SOAP also permits serialization of data that is neither a Struct nor an Array, for example data such as is found in a Directed-Labeled-Graph Data Model in which a single node has many distinct accessors, some of which occur more than once. SOAP serialization does not require that the underlying data model make an ordering distinction among accessors, but if such an order exists, the accessors MUST be encoded in that sequence.
The members of a Compound Value are encoded as accessor elements. When accessors are distinguished by their name (as for example in a struct), the accessor name is used as the element name. Accessors whose names are local to their containing types have unqualified element names; all others have qualified names.
The following is an example of a struct of type "Book":
And this is a schema fragment describing the above structure:
Below is an example of a type with both simple and complex members. It shows two levels of referencing. Note that the "href" attribute of the "Author" accessor element is a reference to the value whose "id" attribute matches. A similar construction appears for the "Address".
The form above is appropriate when the "Person" value and the "Address" value are multi-reference. If these were instead both single-reference, they SHOULD be embedded, as follows:
If instead there existed a restriction that no two persons can have the same address in a given instance and that an address can be either a Street-address or an Electronic-address, a Book with two authors would be encoded as follows:
Serializations can contain references to values not in the same resource:
And this is a schema fragment describing the above structures:
SOAP arrays are defined as having a type of "SOAP-ENC:Array" or a type derived there from (see also rule 8). Arrays are represented as element values, with no specific constraint on the name of the containing element (just as values generally do not constrain the name of their containing element).
Arrays can contain elements which themselves can be of any type, including nested arrays. New types formed by restrictions of SOAP-ENC:Array can also be created to represent, for example, arrays limited to integers or arrays of some user-defined enumeration.
The representation of the value of an array is an ordered sequence of elements constituting the items of the array. Within an array value, element names are not significant for distinguishing accessors. Elements may have any name. In practice, elements will frequently be named so that their declaration in a schema suggests or determines their type. As with compound types generally, if the value of an item in the array is a single-reference value, the item contains its value. Otherwise, the item references its value via an "href" attribute.
The following example is a schema fragment and an array containing integer array members.
In that example, the array "myFavoriteNumbers" contains several members each of which is a value of type SOAP-ENC:int. This can be determined by inspection of the SOAP-ENC:arrayType attribute. Note that the SOAP-ENC:Array type allows unqualified element names without restriction. These convey no type information, so when used they must either have an xsi:type attribute or the containing element must have a SOAP-ENC:arrayType attribute. Naturally, types derived from SOAP-ENC:Array may declare local elements, with type information.
As previously noted, the SOAP-ENC schema contains declarations of elements with names corresponding to each simple type in the "XML Schema Part 2: Datatypes" Specification . It also contains a declaration for "Array". Using these, we might write
Arrays can contain instances of any subtype of the specified arrayType. That is, the members may be of any type that is substitutable for the type specified in the arrayType attribute, according to whatever substitutability rules are expressed in the schema. So, for example, an array of integers can contain any type derived from integer (for example "int" or any user-defined derivation of integer). Similarly, an array of "address" might contain a restricted or extended type such as "internationalAddress". Because the supplied SOAP-ENC:Array type admits members of any type, arbitrary mixtures of types can be contained unless specifically limited by use of the arrayType attribute.
Types of member elements can be specified using the xsi:type attribute in the instance, or by declarations in the schema of the member elements, as the following two arrays demonstrate respectively.
Array values may be structs or other compound values. For example an array of "xyz:Order" structs :
Arrays may have other arrays as member values. The following is an example of an array of two arrays, each of which is an array of strings.
The element containing an array value does not need to be named "SOAP-ENC:Array". It may have any name, provided that the type of the element is either SOAP-ENC:Array or is derived from SOAP-ENC:Array by restriction. For example, the following is a fragment of a schema and a conforming instance array.
Arrays may be multi-dimensional. In this case, more than one size will appear within the asize part of the arrayType attribute:
While the examples above have shown arrays encoded as independent elements, array values MAY also appear embedded and SHOULD do so when they are known to be single reference.
The following is an example of a schema fragment and an array of phone numbers embedded in a struct of type "Person" and accessed through the accessor "phone-numbers":
Here is another example of a single-reference array value encoded as an embedded element whose containing element name is the accessor name:
SOAP provides support for partially transmitted arrays, known as "varying" arrays in some contexts . A partially transmitted array indicates in an "SOAP-ENC:offset" attribute the zero-origin offset of the first element transmitted. If omitted, the offset is taken as zero.
The following is an example of an array of size five that transmits only the third and fourth element counting from zero:
<SOAP-ENC:Array SOAP-ENC:arrayType="xsd:string" SOAP-ENC:offset="">
SOAP provides support for sparse arrays. Each element representing a member value contains a "SOAP-ENC:position" attribute that indicates its position within the array. The following is an example of a sparse array of two-dimensional arrays of strings. The size is 4 but only position 2 is used:
If the only reference to array-1 occurs in the enclosing array, this example could also have been encoded as follows:
The encoding rules just cited are not limited to those cases where the accessor names are known in advance. If accessor names are known only by inspection of the immediate values to be encoded, the same rules apply, namely that the accessor is encoded as an element whose name matches the name of the accessor, and the accessor either contains or references its value. Accessors containing values whose types cannot be determined in advance MUST always contain an appropriate xsi:type attribute giving the type of the value.
Similarly, the rules cited are sufficient to allow serialization of compound types having a mixture of accessors distinguished by name and accessors distinguished by both name and ordinal position. (That is, having some accessors repeated.) This does not require that any schema actually contain such types, but rather says that if a type-model schema does have such types, a corresponding XML syntactic schema and instance may be generated.
Similarly, it is valid to serialize a compound value that structurally resembles an arrray but is not of type (or subtype) SOAP-ENC:Array. For example:
An omitted accessor element implies either a default value or that no value is known. The specifics depend on the accessor, method, and its context. For example, an omitted accessor typically implies a Null value for polymorphic accessors (with the exact meaning of Null accessor-dependent). Likewise, an omitted Boolean accessor typically implies either a False value or that no value is known, and an omitted numeric accessor typically implies either that the value is zero or that no value is known.
The SOAP root attribute can be used to label serialization roots that are not true roots of an object graph so that the object graph can be deserialized. The attribute can have one of two values, either "1" or "0". True roots of an object graph have the implied attribute value of "1". Serialization roots that are not true roots can be labeled as serialization roots with an attribute value of "1" An element can explicitly be labeled as not being a serialization root with a value of "0".
The SOAP root attribute MAY appear on any subelement within the SOAP Header and SOAP Body elements. The attribute does not have a default value.
This section describes how to use SOAP within HTTP with or without using the HTTP Extension Framework. Binding SOAP to HTTP provides the advantage of being able to use the formalism and decentralized flexibility of SOAP with the rich feature set of HTTP. Carrying SOAP in HTTP does not mean that SOAP overrides existing semantics of HTTP but rather that the semantics of SOAP over HTTP maps naturally to HTTP semantics.
SOAP naturally follows the HTTP request/response message model providing SOAP request parameters in a HTTP request and SOAP response parameters in a HTTP response. Note, however, that SOAP intermediaries are NOT the same as HTTP intermediaries. That is, an HTTP intermediary addressed with the HTTP Connection header field cannot be expected to inspect or process the SOAP entity body carried in the HTTP request.
HTTP applications MUST use the media type "text/xml" according to RFC 2376  when including SOAP entity bodies in HTTP messages.
Although SOAP might be used in combination with a variety of HTTP request methods, this binding only defines SOAP within HTTP POST requests (see section 7 for how to use SOAP for RPC and section 6.3 for how to use the HTTP Extension Framework).
The SOAPAction HTTP request header field can be used to indicate the intent of the SOAP HTTP request. The value is a URI identifying the intent. SOAP places no restrictions on the format or specificity of the URI or that it is resolvable. An HTTP client MUST use this header field when issuing a SOAP HTTP Request.
soapaction = "SOAPAction" ":"
[ <"> URI-reference <"> ]
The presence and content of the SOAPAction header field can be used by servers such as firewalls to appropriately filter SOAP request messages in HTTP. The header field value of empty string ("") means that the intent of the SOAP message is provided by the HTTP Request-URI. No value means that there is no indication of the intent of the message.
SOAP HTTP follows the semantics of the HTTP Status codes for communicating status information in HTTP. For example, a 2xx status code indicates that the client's request including the SOAP component was successfully received, understood, and accepted etc.
In case of a SOAP error while processing the request, the SOAP HTTP server MUST issue an HTTP 500 "Internal Server Error" response and include a SOAP message in the response containing a SOAP Fault element (see section 4.4) indicating the SOAP processing error.
A SOAP message MAY be used together with the HTTP Extension Framework  in order to identify the presence and intent of a SOAP HTTP request.
Whether to use the Extension Framework or plain HTTP is a question of policy and capability of the communicating parties. Clients can force the use of the HTTP Extension Framework by using a mandatory extension declaration and the "M-" HTTP method name prefix. Servers can force the use of the HTTP Extension Framework by using the 510 "Not Extended" HTTP status code. That is, using one extra round trip, either party can detect the policy of the other party and act accordingly.
The extension identifier used to identify SOAP using the Extension Framework is
Example 3 SOAP HTTP Using POST
POST /StockQuote HTTP/1.1
Example 4 SOAP Using HTTP Extension Framework
M-POST /StockQuote HTTP/1.1
One of the design goals of SOAP is to encapsulate and exchange RPC calls using the extensibility and flexibility of XML. This section defines a uniform representation of remote procedure calls and responses.
Although it is anticipated that this representation is likely to be used in combination with the encoding style defined in section 5 other representations are possible. The SOAP encodingStyle attribute (see section 4.3.2) can be used to indicate the encoding style of the method call and or the response using the representation described in this section.
Using SOAP for RPC is orthogonal to the SOAP protocol binding (see section 6). In the case of using HTTP as the protocol binding, an RPC call maps naturally to an HTTP request and an RPC response maps to an HTTP response. However, using SOAP for RPC is not limited to the HTTP protocol binding.
To make a method call, the following information is needed:
SOAP relies on the protocol binding to provide a mechanism for carrying the URI. For example, for HTTP the request URI indicates the resource that the invocation is being made against. Other than it be a valid URI, SOAP places no restriction on the form of an address (see  for more information on URIs).
RPC method calls and responses are both carried in the SOAP Body element (see section 4.3) using the following representation:
Applications MAY process requests with missing parameters but also MAY return a fault.
Because a result indicates success and a fault indicates failure, it is an error for the method response to contain both a result and a fault.
Additional information relevant to the encoding of a method request but not part of the formal method signature MAY be expressed in the RPC encoding. If so, it MUST be expressed as a subelement of the SOAP Header element.
An example of the use of the header element is the passing of a transaction ID along with a message. Since the transaction ID is not part of the signature and is typically held in an infrastructure component rather than application code, there is no direct way to pass the necessary information with the call. By adding an entry to the headers and giving it a fixed name, the transaction manager on the receiving side can extract the transaction ID and use it without affecting the coding of remote procedure calls.
Not described in this document are methods for integrity and privacy protection. Such issues will be addressed more fully in a future version(s) of this document.
 S. Bradner, "The Internet Standards Process -- Revision 3", RFC2026, Harvard University, October 1996
 S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997
 E. Whitehead, M. Murata, "XML Media Types", RFC2376, UC Irvine, Fuji Xerox Info. Systems, July 1998
 T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, MIT/LCS, U.C. Irvine, Xerox Corporation, August 1998.
 R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, U.C. Irvine, DEC W3C/MIT, DEC, W3C/MIT, W3C/MIT, January 1997
 H. Nielsen, P. Leach, S. Lawrence, "An HTTP Extension Framework", RFC 2774, Microsoft, Microsoft, Agranat Systems
 W3C Recommendation "The XML Specification"
 W3C Recommendation "Namespaces in XML"
 W3C Working Draft "XML Linking Language". This is work in progress.
 W3C Working Draft "XML Schema Part 1: Structures". This is work in progress.
 W3C Working Draft "XML Schema Part 2: Datatypes". This is work in progress.
 Transfer Syntax NDR, in "DCE 1.1: Remote Procedure Call"
 N. Freed, N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC2045, Innosoft, First Virtual, November 1996
POST /StockQuote HTTP/1.1
POST /StockQuote HTTP/1.1
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 500 Internal Server Error
HTTP/1.1 500 Internal Server Error
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