CSPP 51038 SOAP (formerly Simple Object Access Protocol)
What is the point of SOAP? • Create a standard for how XML can be used as a messaging format for distributed programs. • Tricky part is that the history of the evolution of SOAP has made certain aspects of it very hard to understand motivation-wise.
Some facts about SOAP • SOAP no longer stands for Simple Object Access Protocol – This was dropped in 2003 with publication of v 1. 2 – Considered to be a misleading name • Originally was XML-RPC – Created in 1998 as a very lightweight protocol for remote procedure calls – Was basis for development of SOAP several years later – SOAP currently maintained by W 3 C XML working group • SOAP and XML-RPC are both based entirely on XML
SOAP as a messaging protocol • SOAP is fundamentally a stateless, one-way message exchange paradigm • However, applications can create more complex interaction patterns (e. g. , request/response, request/multiple responses, etc. ) by combining such one-way exchanges with features provided by an underlying protocol and/or application-specific information. • SOAP is silent on the semantics of any application-specific data it conveys, as it is on issues such as the routing of SOAP messages, reliable data transfer, firewall traversal, etc. • However, SOAP provides the framework by which applicationspecific information may be conveyed in an extensible manner. Also, SOAP provides a full description of the required actions taken by a SOAP node on receiving a SOAP message.
SOAP • SOAP is made up of three major parts – A generic XML messaging framework – An optional data encoding standard – An optional RPC (remote procedure call) framework • It is possible to use just the messaging framework or messaging framework/encoding standard without using the RPC mechanism (though latter is arguably where much of power/usefulness lies). • The fact that these are separate leads to great confusion about what SOAP is.
Web Services • Note that classic Web Services are made up of three parts – SOAP – WSDL (Web Services Descriptor Language) – UDDI (Universal Description, Discovery, and Integration) • All three are based on XML • SOAP simply defines the structure of the XML document used to transfer the message + possibly conventions for serializing data into XML + convention for representing method call • WSDL and UDDI are covered next class
SOAP: Messaging framework • Just defines a generic message XML schema • Virtually any type of message you can think of can be packaged as a SOAP message. • However, doing so without RPC mechanisms takes only very small advantage of the features defined in the SOAP standard • We now have learned everything necessary to understand SOAP schema: http: //www. w 3. org/2001/06/soap-envelope
General (Basic) Structure SOAP Message SOAP Envelope • Envelope SOAP Header – Defines the content of the message • Header (optional) – Contains destination information, versioning, extensions – Good place for security • Body – Contains payload SOAP Body Payload Document(s) SOAP Fault
General (Basic) Structure SOAP Message <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/encoding/" soap: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/"> <soap: Header>. . . </soap: Header> <soap: Body> <!-- User request code here --> <soap: Fault>. . . </soap: Fault> </soap: Body> </soap: Envelope>
What is encoding. Style? • Note that this general message framework can be used to attach any valid XML-based message in the <body> element. • In the original design of SOAP this message was intended to be serialized data organized as input/output parameter lists wrapped in method calls. • If the intent is to use SOAP message bodies this way, a standard must be developed for representing generic simple and compound types in programming languages in XML. • Note that schema have much of this already but are lacking some specifics.
SOAP encoding • In order to build SOAP messages from our language of choice, we need to know how to serialize data -- ie the rules for representing an integer, string, or floating point number. The serialization of data inside a SOAP message is referred to as encoding • SOAP does this in a language agnostic way, much like CORBA (but not in binary form) • If the encoding. Style attribute does not appear in the message, the receiver cannot make any assumptions about how data will be represented within the message
SOAP Encoding • You may be wondering about the relationship between encoding and XML Schemas – Encoding can make use of XML Schemas. – The SOAP Specification defines a single set of (recommended) encoding rules call SOAP encoding is based on XML Schemas and as such it closely models many of the standard types and constructs. The value is http: //schemas. xmlsoap. org/soap/encoding/, which points to the XML Schema that defines the encoding rules. – SOAP encoding rules use XML Schemas heavily, relying on the XML Schema datatypes namespace and the type attribute. – The key difference is that encoding does not mandate XML Schemas. – Encoding rules are simply identified by a URI. The rules implied by that URI could be backed up by nothing more than a verbal agreement, or possibly some written documentation. – This allows developers who do not necessarily need the capabilities of XML Schemas to forego their use and start sending messages with encoding rules based on an accepted URI.
SOAP Encoding • For example, SOAP stipulates that an array of three integers be represented as: <SOAP-ENC: Array SOAP-ENC: array. Type="xsd: int[3]"> <SOAP-ENC: int>8</SOAP-ENC: int> <SOAP-ENC: int>5</SOAP-ENC: int> <SOAP-ENC: int>9</SOAP-ENC: int> </SOAP-ENC: Array> • SOAP also provides a type for representing binary data One approach for working with binary data is to use the base 64 type. We can represent binary data, such as an image file, as an array of bytes in the message. The base 64 type converts binary data to text using the base 64 -encoding algorithm of XML Schemas. There is no relationship between SOAP and base 64 -encoding; If we use it, our application (or implementation of SOAP for your platform) must be able to understand work with base 64 -encoding.
SOAP RPC • The third part of SOAP is an RPC mechanism that turns messages into method calls • We have a generic message structure + data. It requires just a little more work to turn the message into a function call. • Must be a standard way to represent parameters and return values, exceptions, etc. • Note that the encoding and rpc mechanisms are only important if SOAP is being automatically generated/read from the application level (see next slide) in a general way
Sample RPC interface package com. jwsbook. soap; import java. rmi. Remote. Exception; public interface Book. Quote extends java. rmi. Remote { // Get the wholesale price of a book public float get. Book. Price(String ISBN) throws Remote. Exception, Invalid. ISBNException; }
Sample rpc SOAP message <? xml version="1. 0" encoding="UTF-8"? > <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/" xmlns: mh="http: //www. Monson-Haefel. com/jwsbook/Book. Quote"> <soap: Body> <mh: get. Book. Price> <isbn>0321146182</isbn> </mh: get. Book. Price> </soap: Body> </soap: Envelope>
Sample rpc SOAP reply <? xml version="1. 0" encoding="UTF-8"? > <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/" xmlns: mh="http: //www. Monson-Haefel. com/jwsbook/Book. Quote" > <soap: Body> <mh: get. Book. Price. Response> <result>24. 99</result> </mh: get. Book. Price. Response> </soap: Body> </soap: Envelope>
SOAP RPC cartoon VB application Java application Invoice VB-Structure Invoice Java-Structure SOAP client SOAP Server SOAP Message The client application thinks its making a procedure call to a remote module
SOAP transport • Recall that SOAP is just a generic message envelope • Augmented by encodingstyle and simple rpc rules, it becomes a powerful middleware layer for remote procedure calls, if one chooses to use it that way • Now we must consider how to transport SOAP messages -- this is the final ingredient in making it something useful
SOAP protocol bindings • Question: how are SOAP messages transmitted? • Answer: using existing protocols (http, SMTP, etc. ) • This has some obvious advantages vs. defining its own protocol – Piggybacks on security model, general robustness • This has some disadvantages also – What are these? • SOAP defines bindings to different protocols that specify how SOAP is used with that protocol to send messages. – http is most popular
Inside http • http is a simple, flexible protocol • Some examples GET http: //people. cs. uchicago. edu/~asiegel/lottery/lotto. html POST /path/script. cgi HTTP/1. 0 From: frog@jmarshall. com User-Agent: HTTPTool/1. 0 Content-Type: application/x-www-form-urlencoded Content-Length: 32 home=Cosby&favorite+flavor=flies POST /path/script. cgi HTTP/1. 0 From: frog@jmarshall. com User-Agent: HTTPTool/1. 0 Content-Type: text/xml Content-Length: 32 <greeting>hello world</greeting>
Testing http • Good idea to play around with http by connecting to server and issuing http commands • There a two typical ways to do this: – Using telnet, which allows arbitrary commands to be passed to a server • telnet people. cs. uchicago. edu 80 • Note that expect can be useful in automating this – Using a socket library in a programming language (see sock. py on website) • Question: how does the server obtain the uploaded data in each case?
Role of SOAP • Note that the http + XML is the important thing here • SOAP only helps standardize the meaning of the messages that are sent – In terms of datatypes for rpc – In terms of headers, faults, etc. • Note that it is still possible to bypass SOAP and define your own xmlbased protocol, retaining many of the advantages of SOAP.
Sorting out the API’s • In Java the following directly related API’s are available: – SAAJ • SOAP with Attachments API for Java • Provides a relatively low-level interface that allows one to programmatically construct/decompose SOAP messages and send to web server • Intended more tool writers. Good for learning. – JAX-RPC • Java API form XML-based RPC • Java’s rmi framework over SOAP – Compare RMI, CORBA, etc. • Makes developer unaware of SOAP internals – Apache XML-RPC for Java • A framework for remote procedure calls using XML-RPC • Recall that XML-RPC is an alternative protocol to SOAP
Looking deeper into SOAP
Envelope • MUST be the root element of the SOAP message • MUST be associated with SOAP envelope namespace – http: //schemas. xmlsoap. org/soap/envelope – http: //www. w 3. org/2001/06/soap-envelope in SOAP 1. 2 (Oct 15, 2002) • SOAP serialization namespace – Encoding Style attributes can contain a URI describing how the data should be serialized. – Two usual styles (more on this later) • "SOAP Section 5" encoding: http: //www. w 3. org/2001/06/soap-encoding • Literal encoding: (no namespace used – or set to empty string) • SOAP message MUST NOT contain – DTD – Processing Instructions.
Envelope versioning • Version determined by the namespace associated with the Envelope element – SOAP 1. 1 Envelope version: http: //schemas. xmlsoap. org/soap/envelope – If any other namespace used, assume it's a version problem – Versioning problems must generate a SOAP Fault • Example SOAP fault: HTTP/1. 0 500 Internal Server Error Content-Type: text/html; charset="utf-8" Content-length: 311 <env: Envelope xmlns: env="http: //schemas. xmlsoap. org/soap/envelope/"> <env: Body> <env: Fault> <faultcode>env: Version. Mismatch</faultcode> <faultstring>SOAP Envelope Version Mismatch</faultstring> </env: Fault> </env: Body> </env: Envelope>
Envelope Versioning Fault in SOAP 1. 2 • SOAP 1. 2 (Oct 15, 2002) has defined an Upgrade element in the header for the Note that 1. 2 Envelope Version Fault versioning fault: Response is versioned 1. 1 (or whatever <? xml version="1. 0" ? > incoming request is) <env: Envelope xmlns: env="http: //schemas. xmlsoap. org/soap/envelope/"> <env: Header> <upg: Upgrade xmlns: upg="http: //www. w 3. org/2002/06/soap -upgrade" > <envelope qname="ns 1: Envelope" xmlns: ns 1="http: //www. w 3. org/2002/06/soap-envelope" /> </upg: Upgrade> </env: Header> <env: Body> <env: Fault> <faultcode>env: Version. Mismatch</faultcode> <faultstring>Version Mismatch</faultstring> </env: Fault> </env: Body> </env: Envelope>
Header • • • Optional If present, must immediately follow the SOAP Envelope XML element followed by any header entries Uses same namespace as Envelope Often contains meta-information regarding the method call. Examples: – – Security • No security mechanisms yet, but soon Transaction IDs
Header • • • actor attribute defines the URI for which the header elements are intended (i. e. who should process a Header element) must. Understand attribute how to process (default is “ 0” if not present) encoding. Style attribute used to describe how data (such as binary integers) are marshaled into characters in the XML document <env: Header> <t: Transaction. ID xmlns: t="http: //www. cs. uchicago. edu/dangulo/transact" env: must. Understand="1" env: actor="http: //www. cs. uchicago. edu/dangulo/transact" > 42 </t: Transaction. ID> <m: localizations xmlns: m="http: //www. cs. uchicago. edu/dangulo/localize/" env: actor="http: //www. cs. uchicago. edu/dangulo/currency" > <m: language>en</m: language> <m: currency>USD</m: currency> </m: localizations> </env: Header>
actor Attribute • The SOAP message often gets passed through several intermediaries before being processed – For example, a SOAP proxy service might get the message before the target SOAP service • Header may contain information for both – intermediary service – target service • actor attribute specifies which service should process a specific Header element • actor attribute is replaced by role attribute in SOAP 1. 2
Intermediary Services • SOAP requires that an intermediary strip off Header elements specified for that intermediary before passing the message to the next service in the chain. • If information in a Header element targeted for an intermediary is also needed by another service in the chain – The intermediary service may insert additional Header elements with an actor attribute that specifies the downstream service • In fact, any service may insert any Header elements that it deems necessary • If a Header element has no actor attribute – It is assumed to be destined for the final recipient – This is equivalent to adding an actor attribute with the URL of the final recipient
must. Understand Attribute • Also put on a Header element • If its value is "1" – recipient is required to understand make proper use of the information supplied by that element – intended for situations where recipient can't do its job unless it knows what to do with the specific information supplied by this particular element • Examples of use – Client is upgraded to a new version which includes extra information – username – security
must. Understand Attribute • If the recipient does not understand this element – Must respond with a SOAP Fault HTTP/1. 0 500 Internal Server Error Content-Type: text/xml; charst="utf-8" Content-length: 287 <env: Envelope xmlns: env="http: //schemas. xmlsoap. org/soap/envelope/"> <env: Body> <env: Fault> <faultcode>env: Must. Understand</faultcode> <faultstring>SOAP Must Understand Error</faultcode> <faultactor>http: //www. cs. uchicago. edu/dangulo/transact </faultactor> </env: Fault> </env: Body> </env: Envelope> • faultactor indicates where fault took place • We'll look at Faults in more detail later • Attribute values change to "true" / "false" in SOAP 1. 2
Some examples Taken from W 3 C primer
Sample SOAP message for travel reservation <? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope"> <env: Header> <m: reservation xmlns: m="http: //travelcompany. example. org/reservation" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <m: reference>uuid: 093 a 2 da 1 -q 345 -739 r-ba 5 d-pqff 98 fe 8 j 7 d</m: reference> <m: date. And. Time>2001 -11 -29 T 13: 20: 00. 000 -05: 00</m: date. And. Time> </m: reservation> <n: passenger xmlns: n="http: //mycompany. example. com/employees" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <n: name>Andrew Siegel</n: name> </n: passenger> </env: Header> Next slide. .
<env: Body> <p: itinerary xmlns: p="http: //travelcompany. example. org/reservation/travel"> <p: departure> <p: departing>New York</p: departing> <p: arriving>Los Angeles</p: arriving> <p: departure. Date>2001 -12 -14</p: departure. Date> <p: departure. Time>late afternoon</p: departure. Time> <p: seat. Preference>aisle</p: seat. Preference> </p: departure> <p: return> <p: departing>Los Angeles</p: departing> <p: arriving>New York</p: arriving> <p: departure. Date>2001 -12 -20</p: departure. Date> <p: departure. Time>mid-morning</p: departure. Time> <p: seat. Preference/> </p: return> </p: itinerary> <q: lodging xmlns: q="http: //travelcompany. example. org/reservation/hotels"> <q: preference>none</q: preference> </q: lodging> </env: Body> </env: Envelope>
Sample SOAP reply <? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope"> <env: Header> <m: reservation xmlns: m="http: //travelcompany. example. org/reservation" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <m: reference>uuid: 093 a 2 da 1 -q 345 -739 r-ba 5 d-pqff 98 fe 8 j 7 d</m: reference> <m: date. And. Time>2001 -11 -29 T 13: 35: 00. 000 -05: 00</m: date. And. Time> </m: reservation> <n: passenger xmlns: n="http: //mycompany. example. com/employees" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <n: name>Andrew Siegel</n: name> </n: passenger> </env: Header> Next slide …
<env: Body> <p: itinerary. Clarification xmlns: p="http: //travelcompany. example. org/reservation/travel"> <p: departure> <p: departing> <p: airport. Choices> JFK LGA EWR </p: airport. Choices> </p: departing> </p: departure> <p: return> <p: arriving> <p: airport. Choices> JFK LGA EWR </p: airport. Choices> </p: arriving> </p: return> </p: itinerary. Clarification> </env: Body> </env: Envelope>
Reply continuing conversational exchange <? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope"> <env: Header> <m: reservation xmlns: m="http: //travelcompany. example. org/reservation" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <m: reference>uuid: 093 a 2 da 1 -q 345 -739 r-ba 5 d-pqff 98 fe 8 j 7 d</m: reference> <m: date. And. Time>2001 -11 -29 T 13: 36: 50. 000 -05: 00</m: date. And. Time> </m: reservation> <n: passenger xmlns: n="http: //mycompany. example. com/employees" env: role="http: //www. w 3. org/2003/05/soap-envelope/role/next" env: must. Understand="true"> <n: name>Andrew Siegel</n: name> </n: passenger> </env: Header> <env: Body> <p: itinerary xmlns: p="http: //travelcompany. example. org/reservation/travel"> <p: departure> <p: departing>LGA</p: departing> </p: departure> <p: return> <p: arriving>EWR</p: arriving> </p: return> </p: itinerary> </env: Body> </env: Envelope>
SOAP RPC request with a mandatory header and two input (or "in") parameters <? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope" > <env: Header> <t: transaction xmlns: t="http: //thirdparty. example. org/transaction" env: encoding. Style="http: //example. com/encoding" env: must. Understand="true" >5</t: transaction> </env: Header> <env: Body> <m: charge. Reservation env: encoding. Style="http: //www. w 3. org/2003/05/soap-encoding" xmlns: m="http: //travelcompany. example. org/"> <m: reservation xmlns: m="http: //travelcompany. example. org/reservation"> <m: code>FT 35 ZBQ</m: code> </m: reservation> <o: credit. Card xmlns: o="http: //mycompany. example. com/financial"> <n: name xmlns: n="http: //mycompany. example. com/employees">Andrew Siegel</n: name> <o: number>123456789099999</o: number> <o: expiration>2005 -02</o: expiration> </o: credit. Card> </m: charge. Reservation> </env: Body>
RPC response with two output (or "out") parameters ? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope" > <env: Header> <t: transaction xmlns: t="http: //thirdparty. example. org/transaction" env: encoding. Style="http: //example. com/encoding" env: must. Understand="true">5</t: transaction> </env: Header> <env: Body> <m: charge. Reservation. Response env: encoding. Style="http: //www. w 3. org/2003/05/soap-encoding" xmlns: m="http: //travelcompany. example. org/"> <m: code>FT 35 ZBQ</m: code> <m: view. At> http: //travelcompany. example. org/reservations? code=FT 35 ZBQ </m: view. At> </m: charge. Reservation. Response> </env: Body> </env: Envelope>
RPC response with a "return" value and two "out" parameters <? xml version='1. 0' ? > <env: Envelope xmlns: env="http: //www. w 3. org/2003/05/soap-envelope" > <env: Header> <t: transaction xmlns: t="http: //thirdparty. example. org/transaction" env: encoding. Style="http: //example. com/encoding" env: must. Understand="true">5</t: transaction> </env: Header> <env: Body> <m: charge. Reservation. Response env: encoding. Style="http: //www. w 3. org/2003/05/soap-encoding" xmlns: rpc="http: //www. w 3. org/2003/05/soap-rpc" xmlns: m="http: //travelcompany. example. org/"> <rpc: result>m: status</rpc: result> <m: status>confirmed</m: status> <m: code>FT 35 ZBQ</m: code> <m: view. At> http: //travelcompany. example. org/reservations? code=FT 35 ZBQ </m: view. At> </m: charge. Reservation. Response> </env: Body> </env: Envelope>
Encoding • The encoding. Style attribute can be placed on any element – allowing mixed encoding styles • Two values most often used (anything possible): – "SOAP Section 5" encoding: http: //www. w 3. org/2001/06/soap-encoding – Literal encoding: (no namespace used – or set to empty string) • Also can do base 64 encoding • Can turn it off currently scoped style using an empty string as URL ("") – parent scoped style becomes default again
Document vs. RPC style • Document: <soap: Body> contains one or more child elements called parts. There are no SOAP formatting rules for what the <soap: Body> contains; it contains whatever the sender and the receiver agree upon. ･ • RPC: RPC implies that <soap: Body> contains an element with the name of the method or remote procedure being invoked. This element in turn contains an element for each parameter of that procedure. • See section 5 in http: //www. w 3. org/TR/2003/REC-soap 12 -part 220030624/#soapforrpc
Encoded vs. literal • SOAP Encoding: SOAP encoding is a set of serialization rules defined in section 5 of SOAP 1. 1 and is sometimes referred to as "section 5 encoding. " The rules specify how objects, structures, arrays, and object graphs should be serialized. Generally speaking, an application using SOAP encoding is focused on remote procedure calls and will likely use RPC message style. The rest of this article ignores SOAP encoding and focuses on literal format. • Literal: Data is serialized according to a schema. In practice, this schema is usually expressed using W 3 C XML Schema. Although there are no prescribed rules for serializing objects, structures, and graphs, etc. , the service's schema describes the application-level Infoset of each of the service's messages.
Example document/literal soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/"> <soap: Body> <!-- the following is an XML document described in the service's contract using XML Schema. In this case Example may or may not be the name of a remote procedure being invoked by this message. Also, cust may or may not be the name of a parameter. We know the structure of the XML document but we don't know how the service processes it --> <Example xmlns="http: //example. org/soapformat"> <cust> <Customer> <Name>John Doe</Name> <Id>ABC-1234</Id> </Customer> <Name>Jane Doe</Name> <Id>XYZ-1234</Id> </Customer> </cust> </Example> </soap: Body> </soap: Envelope>
Example rcp/literal <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/"> <soap: Body> <!-- Example is the name of the procedure being invoked cust is a parameter of that procedure. Note that cust is not namespace-qualified. The two Customer elements are contents of the cust parameter. In this case cust can be thought of as an array of Customer items. Note that Customer is namespace qualified but it's in a different namespace than Example. These namespace rules are unique to RPC-style messages and will be explained in the next section --> <x: Example xmlns: x="http: //example. org/soapformat/Example"> <cust> <t: Customer xmlns: t="http: //example. org/soapformat"> <t: Name>John Doe</t: Name> <t: Id>ABC-1234</t: Id> </t: Customer> <t: Name>Jane Doe</t: Name> <t: Id>XYZ-1234</t: Id> </t: Customer> </cust> </x: Example> </soap: Body> </soap: Envelope>
Response • No Special HTTP Response headers (doesn't use SOAPAction: header) • Only special SOAP element is the Fault element and its children • Otherwise, looks like a normal SOAP message <? xml version="1. 0" encoding="UTF-8"? > <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/" soap: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/" xmlns: xsi="http: //www. w 3. org/1999/XMLSchema-instance" xmlns: xsd="http: //www. w 3. org/1999/XMLSchema"> <soap: Body> <m: Favorite. Color. Response. Msg xmlns: m="http: //www. cs. uchicago. edu/dangulo/soap-methods"> <answer xsi: type="xsd: string">Red. . . No, Blue. . . Aarrgh!</answer > </m: Favorite. Color. Response. Msg> </soap: Body> </soap: Envelope>
Fault • The <fault> element is in the body of the SOAP message • 0 or 1 <fault> elements may be in the message • The following subelements may be in the <fault> element <faultcode> One of the following codes (note: the codes are strings) Version. Mismatch The SOAP namespace is incorrect Must. Understand The client sent a header element with a Must. Understand set to 1, and the server did not understand it Client The message was incorrectly formed Server The server had a problem <faultstring> The error as a string <faultactor> Who reported the error <detail> Details of the problem
Bridge of Death Example • Request <? xml version="1. 0" encoding="UTF-8"? > <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/" soap: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/" xmlns: xsi="http: //www. w 3. org/1999/XMLSchema-instance" xmlns: xsd="http: //www. w 3. org/1999/XMLSchema"> <soap: Body> <m: Favorite. Color. Request. Msg xmlns: m="http: //www. cs. uchicago. edu/dangulo/soap-methods/"> <question xsi: type="xsd: string"> What is your favorite color? </question > </m: Favorite. Color. Request. Msg> </soap: Body> </soap: Envelope>
Bridge of Death Response Example • Response <? xml version="1. 0" encoding="UTF-8"? > <soap: Envelope xmlns: soap="http: //schemas. xmlsoap. org/soap/envelope/" soap: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/" xmlns: xsi="http: //www. w 3. org/1999/XMLSchema-instance" xmlns: xsd="http: //www. w 3. org/1999/XMLSchema"> <soap: Body> <m: Favorite. Color. Response. Msg xmlns: m="http: //www. cs. uchicago. edu/dangulo/soap-methods"> <answer xsi: type="xsd: string">Red. . . No, Blue. . . Aarrgh!</answer > </m: Favorite. Color. Response. Msg> </soap: Body> </soap: Envelope>
Data Types • The data type for a given value is never undefined in SOAP • SOAP distinguished between simple types and complex types – A simple type does not contain any named parts, it just contains a single piece of data • Example: string • Example: int – A complex type contains multiple pieces of data that have some relation to each other • Similar to structs or classes or arrays • Individual pieces of data may be accessed by using – an ordinal position in a sequence of values (like arrays) – values that are keys to an associative array (like hash tables) – the names of the constituent parts (like C structs) • There is always a way to distinguish a specific data value within a complex value – referred to as the "accessor" • A names subcomponent of a complex type may be a complex type itself
Built-in Data Types
References • We briefly saw how to declare these in DTDs • Let's see how to use these <round. Table. Members> <member> <name>King Arthur</name> <position>King</position> </member> <name>Sir Robin</name> <position>Knight</position> <king>King Arthur</king> </member> <name>Sir Galahad</name> <position>Knight</position> <king>King Arthur</king> </member> Lots of unnecessary duplication
References • References help you eliminate unnecessary duplication (normalization) <round. Table. Members> <member id="Arthur"> <name>King Arthur</name> <position>King</position> </member> <name>Sir Robin</name> <position>Knight</position> <king href="#Arthur" /> </member> <name>Sir Galahad</name> <position>Knight</position> <king href="#Arthur" /> </member> No more unnecessary duplication
References • May not save space if the data items are small • Should save space if the data items are larger • Are necessary to link objects. – Graphs – Organizational structure (like round table in previous slide) – Students' class enrollment
Indicating Type • Every element that contains a value must also indicate the type of the data • In SOAP, these types may be specified – By using the xsi: type attribute • with a valid type identifier, such as xsd: string or xsd: int – By being an element of an array that already constrains the type of its contents – By being related to some type that is defined in an XML Schema • So far, we've only seen examples of the first method • SOAP (by itself – without WSDL), usually uses the first method (and the second) • There are two different string type declarations: – xsd: string from XML Schema – SOAP-ENC: string from SOAP Section 5 • This one allows for id and href attributes
Indicating Type • Example of dynamically declaring the type inside the XML document itself <? xml version="1. 0" encoding="UTF-8"? > <SOAP-ENV: Envelope. . . <SOAP-ENV: Body>. . . <lue xsi: type="xsd: int">42</lue> <bq xsi: type="xsd: string">What is your color? </bq> <bq xsi: type="SOAP-ENC: string">Color? </bq>. . . </SOAP-ENV: Body> </SOAP-ENV: Envelope>
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