SOAP (Simple Object Access Protocol)

1
SOAP (Simple Object Access Protocol)

• Knarig Arabshian
• Department of Computer Science
• Columbia University
• knarig_at_cs.columbia.edu
• April 24, 2002

2
Overview

• What is SOAP?
• Details of the protocol
• SOAP and SIP Emergency Notification
• Conclusion
• References

3
What is SOAP?
4
What is SOAP?

• Lightweight protocol used for exchange of
  messages in a decentralized, distributed
  environment
• Facilitates interoperability in a
  platform-independent manner
• Used for Remote Procedure Calls
• W3C note defines the use of SOAP with XML as
  payload and HTTP as transport, but other
  transport protocols can be used such as SMTP and
  SIP.

5
Advantages of SOAP

• Uses HTTP which is widely used and scalable
• Wide remote system interoperability
• Flexible for growth because of XML properties
• It but can be used for RPC.

6
Disadvantages of SOAP

• No good way to describe the serialization pattern
  (XML schema is optional at this point)
• Parsing of SOAP packet and mapping to objects
  reduces performance
• Doesnt implement security because it is a wire
  protocolrelies on HTTP

7
SOAP Elements

• Envelope (mandatory)
• Top element of the XML document representing the
  message
• Header (optional)
• Determines how a recipient of a SOAP message
  should process the message
• Adds features to the SOAP message such as
  authentication, transaction management, payment,
  message routes, etc
• Body (mandatory)
• Exchanges information intended for the recipient
  of the message.
• Typical use is for RPC calls and error reporting.

8
SOAP Elements

• SOAP Encoding
• Envelope package
• Header/Body pattern
• Similar to how HTTP works

Header
Body
9
Simple Example
ltEnvelopegt ltHeadergt lttransIdgt345lt/transId
gt lt/Headergt ltBodygt ltAddgt
ltn1gt3lt/n1gt ltn2gt4lt/n2gt lt/Addgt
lt/Bodygt lt/Envelopegt
c Add(n1, n2)
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SOAP Request
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//sche
mas.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ltSOAP-ENVHeadergt
ltttransId xmlnsthttp//a.com/transgt345lt/ttra
nsIdgt lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//a.com/Calculatorgt
ltn1gt3lt/n1gt ltn2gt4lt/n2gt
lt/mAddgt lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt
11
SOAP Request
Scopes the message to the SOAP namespace
describing the SOAP envelope
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//schem
as.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ...etc... lt/SOAP-ENVEnvelope
gt
Establishes the type of encoding that is used
within the message (the different data types
supported)
12
SOAP Request
Qualifies transId
...etc... ltSOAP-ENVHeadergt
ltttransId xmlnsthttp//a.com/transgt1234lt/ttr
ansIdgt lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//a.com/Calculatorgt
ltn1gt3lt/n1gt ltn1gt4lt/n2gt
lt/mAddgt lt/SOAP-ENVBodygt ...etc...
Defines the method
13
SOAP Response
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//sche
mas.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ltSOAP-ENVHeadergt
ltttransId xmlnsthttp//a.com/transgt345lt/ttra
nsIdgt lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAddResponse xmlnsmhttp//a.com/Calculator
gt ltresultgt7lt/resultgt
lt/mAddResponsegt lt/SOAP-ENVBodygt lt/SOAP-ENVEn
velopegt
14
SOAP Response
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//sch
emas.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ltSOAP-ENVHeadergt
ltttransId xmlnsthttp//a.com/transgt345lt/ttra
nsIdgt lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAddResponse xmlnsmhttp//a.com/Calculator
gt ltresultgt7lt/resultgt
lt/mAddResponsegt lt/SOAP-ENVBodygt lt/SOAP-ENVEn
velopegt
Response typically uses method name with
Response appended
15
SOAP Fault

• Used to carry error and/or status information
  within a SOAP message
• Appears within the SOAP body
• Defines the following
• faultcode (mandatory)
• algorithmic mechanism for identifying the fault
• defined in the SOAP spec
• Faultstring (mandatory)
• human readable explanation of the fault

16
SOAP Fault

• faultactor (optional)
• information about who caused the fault to happen
• URI value identifying the source
• Detail
• error information related only to the Body
  element.
• if not present then indicates that the fault is
  not related to the Body element.

17
SOAP Fault Example
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//sch
emas.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ltSOAP-ENVBodygt
ltSOAP-ENVFaultgt ltfaultcodegtSOAP-ENVServ
erlt/faultcodegt ltfaultstringgtInternal
Application Errorlt/faultstringgt ltdetail
xmlnsfhttp//www.a.com/CalculatorFaultgt
ltferrorCodegt794634lt/ferrorCodegt
ltferrorMsggtDivide by zerolt/ferrorMsggt
lt/detailgt lt/SOAP-ENVFaultgt
lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt
18
SOAP Encoding

• Based on a simple type system that has common
  features with programming languages and databases
• Types are either simple (scalar) or compound
  which is a composite of several parts
• An XML schema which is consistent with this type
  system can be constructed
• Use of schemas is encouraged but NOT required

19
Arrays

• int a3 1, 2, 3
• b Add(ina)

ltmAdd xmlnsmhttp//a.com/Calculator xmlnsSOAP-
ENC"http//schemas.xmlsoap.org/soap/encoding/gt
lta SOAP-ENCarrayTypexsdint3gt
ltSOAP-ENCintgt1lt/SOAP-ENCintgt
ltSOAP-ENCintgt2lt/SOAP-ENCintgt
ltSOAP-ENCintgt3lt/SOAP-ENCintgt lt/agt lt/mAddgt
20
Structures

• typedef struct
• char author64
• char title200
• int year
• Book
• Book crimAndPunishment
• B Publish(crimeAndPunishment)
• ltmPublish xmlnsmhttp//a.com/Publishing
• xmlnsSOAP-ENC"http//schemas.xmlsoap.org/soap/en
  coding/gt
• ltauthor type"xsdstring"/gtFyodor
  Dostoevskylt/authorgt
• lttitle type"xsdstring"gtCrime and
  Punishmentlt/titlegt
• ltyear type"xsdinteger"gt1917lt/yeargt
• lt/mPublishgt

21
XML Schemas

• Defines the structure, content and semantics of
  XML documents
• Simple types
• Integers, strings, floats, time, etc.
• Compound (complex) types
• Arrays, structures

22
Example of XML Schema
ltelement name"Book"gtltcomplexTypegt  ltelement
name"author" type"xsdstring"/gt  ltelement
nametitle" type"xsdstring"/gt  ltelement
nameyear" type"xsdinteger"/gtlt/complexTypegt lt/
elementgt
lteBookgt   ltauthorgtFyodor Dostoevskylt/authorgt   
lttitlegtCrime and Punishmentlt/titlegt   ltyeargt1917lt
/yeargtlt/eBookgt
23
HTTP Request
POST /Calculator.pl HTTP/1.0 Host
www.a.com Accept text/ Content-type
text/xml Content-length nnnn SOAPAction
http//www.a.com/CalculatorAdd CRLF ltSOAP-E
NVEnvelope xmlnsSOAP-ENVhttp//schemas.xml
soap.org/soap/envelope/ SOAP-ENVencodingStyle
"http//schemas.xmlsoap.org/soap/encoding/gt
ltSOAP-ENVHeadergt ltttransId
xmlnsthttp//a.com/transgt345lt/ttransIdgt
lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//a.com/Calculatorgt
ltn1gt3lt/n2gt ltn1gt4lt/n2gt lt/mAddgt
lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt
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HTTP Response
HTTP/1.0 200 OK Content-type text/xml Content-len
gth nnnn CRLF ltSOAP-ENVEnvelope
xmlnsSOAP-ENVhttp//schemas.xmlsoap.org/soap/en
velope/ SOAP-ENVencodingStyle"http//schemas
.xmlsoap.org/soap/encoding/gt
ltSOAP-ENVHeadergt ltttransId
xmlnsthttp//a.com/transgt345lt/ttransIdgt
lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAddResponse xmlnsmhttp//a.com/Calculatorgt
ltresultgt7lt/resultgt
lt/mAddResponsegt lt/SOAP-ENVBodygt lt/SOAP-ENVEn
velopegt
25
SOAPAction

• The SOAPAction HTTP request header field can be
  used to indicate the intent of the SOAP HTTP
  request.
• Used by servers, such as firewalls, to
  appropriately filter SOAP request messages in
  HTTP.
• If value is empty string (""), 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.

26
SOAPAction
POST /Calculator.pl HTTP/1.0 Host
www.a.com Accept text/ Content-type
text/xml Content-length nnnn SOAPAction
http//www.a.com/CalculatorAdd CRLF ltSOAP-E
NVEnvelope xmlnsSOAP-ENVhttp//schemas.xml
soap.org/soap/envelope/ SOAP-ENVencodingStyle
"http//schemas.xmlsoap.org/soap/encoding/gt
ltSOAP-ENVHeadergt ltttransId
xmlnsthttp//a.com/transgt345lt/ttransIdgt
lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//a.com/Calculatorgt ...etc..
.
27
SOAP and SIP
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SOAP and SIP Emergency Notification

• SIP (Session Initiation Protocol) is a text-based
  signaling protocol used to establish multimedia
  sessions on the Internet.
• Similar to HTTP and SMTP
• Extended to support event notification using
  SUBSCRIBE and NOTIFY methods
• Send a NOTIFY message with SOAP payload
• Body of the SOAP message will invoke a remote
  procedure relevant to the particular emergency
  event
• Use XML Schema to specify different emergency
  events handled and parameters needed

29
SOAP and SIP

• lt?xml version"1.0" ?gtltxsschema
  xmlnsxs"http//www.w3.org/2001/XMLSchema"gt
• ltxscomplexType name"EmergencyType"gt
• ltxssequencegt
• ltxselement name"Fire" type"Fire"/gt
• ltxselement name"Earthquake"
  type"Earthquake"/gt
• lt/xssequencegt
• lt/xscomplexTypegt
• ltxscomplexType name"Fire"gt
• ltxssequencegt
• ltxselement name"location" type"string"/gt
• ltxselement name"severity"
  type"string"/gtlt/xssequencegt
• lt/xscomplexTypegt
• ltxscomplexType name"Earthquake"gt
• ltxssequencegt
• ltxselement name"location" type"string"/gt
• ltxselement name"scale" type"decimal"/gt
• lt/xssequencegt
• lt/xscomplexTypegt
• lt/xsschemagt

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SOAP and SIP
NOTIFY sipknarig_at_128.59.19.1945063 SIP/2.0 Via
SIP/2.0/UDP 128.59.19.1945063 CSeq 3
NOTIFY Contact sipknarig_at_128.59.19.1945063 From
sipcisalpino.cs.columbia.edu5063 Call-Info
www.cs.columbia.edu/knarig Date Wed, 24 Apr
2002 145705 GMT Content-Type
application/soap Call-ID 461662663_at_128.59.19.194
Event emergency To sipknarig_at_cs.columbia.edu Co
ntent-Length 494
lt?xml version'1.0'?gtltSOAP-ENVEnvelope
xmlnsxsi"http//www.w3.org/1999/XMLSchema-instan
ce" xmlnsSOAP-ENV"http//schemas.xmlsoap.org/soa
p/envelope/" xmlnsSOAP-ENC"http//schemas.xmlsoa
p.org/soap/encoding/" SOAP-ENVencodingStyle"http
//schemas.xmlsoap.org/soap/encoding/"
xmlnsxsd"http//www.w3.org/1999/XMLSchema"gtltSO
AP-ENVBodygtltFiregt ltlocation
xsitype"xsdstring"gtMuddlt/locationgt
ltseverity xsitype"xsdstring"gtsmokelt/severitygt
lt/Firegt lt/SOAP-ENVBodygtlt/SOAP-ENVEnvelopegt
31
Columbia SIP user agent (sipc)

• Media
• Audio, video, text, white board
• Screen sharing
• Shared web browsing
• Advanced
• Presence, instant messaging
• Conference control
• Emergency notification and handling
• Device control

32
Columbia SIP user agent (sipc)
Invoke Emergency Services
Calls 911 by connecting to the local PSAP
Receive emergency notification alerts from
various event servers that user has subscribed to
33
Detailed overview of architecture
3) Sipc contacts notification server and gets
list of emergency events user can subscribe to
2) Generic emergency address emergenycy_at_state.ny.
us is added to sipc
1) Event generators publish their events to
notification server
Fire
sos_at_leonia.nj.us Notification server (sipd)
Earthquake
5) Sipc gets XML schema reference from
notification server that will generate a form
which queries for the events properties. Sipc
then updates its subscription to the notification
server with the filtered expressions
4) User subscribes to event it wants to be
notified of
34
Detailed overview of architecture
3)Sipc will process SOAP body and invoke the
procedure callsuch as flashing of lights
1) Fire occurs and event generator notifies sipd
2) Sipd will process parameters of the fire and
send a NOTIFY to sipc including SOAP body
Fire
Emergency_at_state.ny.us Notification server (sipd)
Earthquake
35
Example of Notification Flashing of Lights

• Emergency event notification invokes multiple
  calls of the SIP DO method
• This causes the lamp (connected to the PC by an
  X10 device) to flash

lamp
serial port
DO siplamp_at_cs.columbia.edu SIP/2.0 .. ltControlgt
ltActiongtturn lamp onlt/Actiongt lt/Controlgt
X10 device
36
Conclusions

• SOAP is a scalable and widely used wiring
  protocol
• It is still not an industry standard and needs
  fine-tuning
• Using SIP and SOAP for emergency notification is
  simple and effective

37
References

• http//www.endurasoft.com/soap
• http//www.w3.org/TR/SOAP/
• http//www.microsoft.com/mind/0100/soap/soap.asp
• Scribner K., Stiver M.C., Understanding SOAP,
  Indianapolis, Indiana, 2000