1. Web Services (NSWI145)
Lecture 03: SOAP
Martin Nečaský, Ph.D.
Faculty of Mathematics and Physics
Charles University in Prague, Czech Republic
Summer 2013

2. SOAP Reminder
 example
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3. SOAP Processing Model
 SOAP message travels along path of SOAP
nodes = SOAP message path
 from initial SOAP sender
• point of origin
 to ultimate SOAP receiver
• final destination
 passes zero or more SOAP intermediaries
 each SOAP node is identified by unique URI
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4. SOAP Processing Model
Sender Intermediary
…
Intermediary Receiver
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5. SOAP Processing Model
 processing SOAP message by SOAP node:
 check if message is valid SOAP message
 process SOAP standard elements
• body entries MUST be processed by ultimate SOAP
receiver and MAY NOT be processed by SOAP
intermediary
• header blocks MAY be processed by any SOAP
intermediary and ultimate SOAP receiver
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6. SOAP Processing Model
 processing SOAP message by SOAP
intermediary results in:
 generating single SOAP fault, OR
 forwarding (optionally) updated SOAP message
and generating and sending zero or more
additional SOAP messages
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7. SOAP Processing Model
 each header block in SOAP message has optional
attributes which adjust how SOAP nodes on SOAP
message path process header block
 role
 mustUnderstand
 relay
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8. SOAP Processing Model
Attribute role
 each SOAP node assumes its roles (one or
more) for processing given SOAP message
 must be invariant during processing single SOAP
message
 each header block has specified targeted role
by optional role attribute
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9. SOAP Processing Model
Attribute role
 value of type xs:anyURI
 3 standard values
 none
 next
 ultimateReceiver
 application-specific roles can be created
 each must have its own URI
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10. SOAP Processing Model
Attribute role
 value none
 SOAP nodes MUST NOT act in this role
• i.e. header block does not target any SOAP node
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11. SOAP Processing Model
Attribute role
 value ultimateReceiver
 each SOAP ultimate receiver must act in this role
• i.e. header block targets each SOAP node that assumes
being ultimate SOAP receiver
 default value when role is not specified
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12. SOAP Processing Model
Attribute role
 value next
 each SOAP intermediary and ultimate SOAP
receiver MUST act in this role
• i.e. header targets any SOAP node except initial SOAP
sender which is meaningless
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13. SOAP Processing Model
Attribute role
 application specific value
 header targets each SOAP node that assumes to
play that application-specific role
 e.g.:
• http://www.ksi.mff.cuni.cz/soap/roles/Cache
• http://www.ksi.mff.cuni.cz/soap/roles/Log
• http://www.ksi.mff.cuni.cz/soap/roles/Encrypt
• http://www.ksi.mff.cuni.cz/soap/roles/Annotate
• http://www.ksi.mff.cuni.cz/soap/roles/Backup
• …
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14. SOAP Processing Model
Attribute role
 SOAP node is targeted by header block iff
SOAP node assumed role
=
header block role
 targeted SOAP node may process header
block
 processing according to application specific rules
of that block (which is not part of SOAP)
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15. SOAP Processing Model
Attribute role
 SOAP does not specify how SOAP node
determines its roles
 entirely application-specific task
 can be known a priori as well as determined
dynamically in run-time
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16. SOAP Processing Model
Attribute role Example
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17. SOAP Processing Model
Attribute mustUnderstand
 value of type xs:boolean
 default value: false
 if true, targeted SOAP node must process
header block
 header block is called mandatory header block for
that SOAP node
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18. SOAP Processing Model
Attribute mustUnderstand
 inability to process mandatory header block
means that
 single SOAP fault is generated
• with code MustUnderstand
 original SOAP message is not forwarded any
further
 all further processing of original SOAP message is
cancelled
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19. SOAP Processing Model
Attribute mustUnderstand Example
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20. SOAP Processing Model
Attribute relay
 value of type xs:boolean
 default value: false
 specifies forwarding header blocks by targeted
SOAP intermediaries
 relayable vs. non-relayable header blocks
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21. SOAP Processing Model
Processing SOAP Header Blocks
1. determine roles
2. identify targeting header blocks
3. if one or more mandatory header blocks are
not understood
 generate SOAP fault
 exit
 process header blocks
 mandatory and others optionally
1. if you are SOAP intermediary then relay
header blocks
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22. SOAP Processing Model
Processing SOAP Header Blocks
 SOAP intermediary relays header blocks as
follows:
 header block targeting SOAP intermediary
• processed block is removed
• ignored and non-relayable block is removed
• ignored and relayable block is retained
 header block not targeting SOAP intermediary is
retained
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23. SOAP Processing Model
Processing SOAP Header Blocks
 SOAP intermediary acting exactly as described
in previous two slides is called forwarding
SOAP intermediary
 SOAP intermediary which moreover adds,
removes or updates header blocks is called
active SOAP intermediary
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24. SOAP Processing Model
Relaying SOAP Header Blocks
SOAP Header
Header Block A
role="Annotate"
mustUnderstand="true"
Header Block B
role="Annotate"
Sender relay="true"
Header Block C
role="next"
Header Block D
role="Log"
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25. SOAP Processing Model
Relaying SOAP Header Blocks
SOAP Header SOAP Header
Header Block A Header Block A
role="Annotate" role="Annotate"
mustUnderstand="true" mustUnderstand="true"
Header Block B Header Block B
role="Annotate"
Forwarding role="Annotate"
Sender relay="true" relay="true"
Intermediary
roles:
Header Block C Header Block C
Annotate
role="next" role="next"
next
Header Block D
ignores: Header Block D
role="Log"
Header Block B role="Log"
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26. SOAP Processing Model
Relaying SOAP Header Blocks
SOAP Header SOAP Header
Header Block A Header Block A
role="Annotate" role="Annotate"
mustUnderstand="true" mustUnderstand="true"
Header Block B Header Block B
role="Annotate" Forwarding role="Annotate"
relay="true" relay="true"
Intermediary
Header Block C roles: Header Block C
role="next" Annotate role="next"
next
Header Block D ignores: Header Block D
role="Log" Header Block B role="Log"
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27. SOAP Processing Model
Relaying SOAP Header Blocks
SOAP Header SOAP Header
Header Block A Header Block A
role="Annotate" role="Annotate"
mustUnderstand="true" mustUnderstand="true"
Header Block B Header Block B
E
role="Annotate" Active role="Annotate"
role="next"
relay="true" relay="true"
Intermediary
Header Block B
Header Block C roles: role="Annotate"
role="next" Annotate relay="true"
next
Header Block D ignores: Header Block D
role="Log" Header Block B role="Log"
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28. SOAP Header vs. Body
 what information should be part of header and what
should be placed in body?
 decision made during application design
Header Body
• may be processed and updated • primary content
by SOAP intermediaries • processed only by ultimate
• SOAP intermediaries provide SOAP receiver
value-added services on base • must be understood by
ultimate SOAP receiver
of header blocks
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29. SOAP Communication Model
 two possible communication models
 RPC-style web services
• RPC/Literal
 document-(or message-)style web services
• RPC/Document
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30. SOAP Communication Model
RPC-style web services
 web service appears as remote object
 request = method call with name and set of
typed arguments
 response = return value
 automatic serialization/deserialization of
method calls and return values
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31. SOAP Communication Model
RPC-style web services
 tightly coupled client and service
 hard-coded
 usually synchronous
 allows for exposing software components as
web services
 servlets, Java RMI objects, ...
 components natively DO NOT exchange XML data
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32. SOAP Communication Model
RPC-style web services Example
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33. SOAP Communication Model
Document-style web services
 exchanging any documents (any information)
 documents encoded in XML
 no automatic serialization/deseralization of
documents in XML
 exchanged documents are primarily encoded in
XML by application
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34. SOAP Communication Model
Document-style web services
 closer to real-world
 communication between real-world
"components" instead of software components
 asynchronous
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35. SOAP Network Protocol Binding
 SOAP does not specify how SOAP messages
are encoded for network transfer
 SOAP message must be encapsulated in a
message conforming to a network protocol
 binding SOAP messages to HTTP, SMTP, FTP, etc. or
even simpler TCP/IP or UDP
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36. SOAP Network Protocol Binding
 particular network protocol influences what
must be implemented at SOAP level
 HTTP natively supports request/response
communication pattern
 UDP natively does not natively support
request/response communication pattern which
must be therefore implemented at SOAP level
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37. SOAP Network Protocol Binding
 different network protocols can be applied on
SOAP message path with one or more SOAP
intermediaries
 web services developers usually do not come
in touch with binding specification
 HTTP used in most cases
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38. SOAP Network Protocol Binding
HTTP Binding
 SOAP messages
 encoded as HTTP messages
 become data part of HTTP message
 supplemented with HTTP headers
• e.g. Host, Content-Length, etc.
 client identifies server via URL, connects using
TCP/IP, issues HTTP request message and
receives HTTP response
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39. SOAP Advantages
 simplicity
 XML is structured and easy to parse
 portability
 no dependency on the underlying platform
 firewall-friendly
 HTTP, SMTP
 open, interoperable standard
 universal acceptance
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40. SOAP Advantages
Modularity
XML modularity
SOAP modularity
code modularity  code re-use
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41. SOAP Advantages
Modularity
 namespaces identify different header block
and body languages and their particular
versions
 different libraries for processing different versions
of SOAP
 different libraries for processing different header
blocks and body
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42. SOAP Advantages
Modularity
SOAP Envelope SOAP v1.1
SOAP Header library
http://schemas.xmlsoap.org/
soap/envelope/
SOAP Body http://www.w3.org/
2003/05/soap-envelope
SOAP v1.2
library
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43. SOAP Advantages
Modularity
SOAP Envelope
SOAP Header
PayPalAPI v 1.0
urn:ebay:api: library
PayPalAPI
SOAP Body
Message PayPalAPI v 1.1
urn:ebay:api: library
PayPalAPI11
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44. SOAP Advantages
Modularity
<?xml version="1.0"?>
<env:Envelope
xmlns:env="http://www.w3.org/2003/05/soap-envelope">
<env:Body xmlns="urn:ebay:api:PayPalAPI" />
</env:Envelope>
<?xml version="1.0"?>
<env:Envelope
xmlns:env="http://www.w3.org/2003/05/soap-envelope">
<env:Body xmlns="urn:ebay:api:PayPalAPI-11" />
</env:Envelope>
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45. SOAP Advantages
Modularity
SOAP Envelope
SOAP Header http://digsig.com/
standard Digital signature
Header Block
library
Header Block http://thirdparty.com/
ws-trans1-0
Transactions 1.0
SOAP Body library
http://fourthparty.com/
ws-trans2-0
Transactions 2.0
library
Summer 2013

46. SOAP Disadvantages
 originally tied to HTTP
 request/response architecture, SOAP performance
suffers
 improved in recent versions
 stateless
 but may be managed by SOAP extensions
 reference by value
 no object references
 XML
Summer 2013