Title: Web Services
1Web Services
2Web Basics
3Internet
- Collection of physically interconnected
computers. - Messages decomposed into packets.
- Packets transmitted from source to destination
using a store-and-forward technique. - Routing algorithm directs packets to destination
4Connection-Oriented Protocol
- Prior to transmission connection is established
between source and destination. Each maintains
state information - Sequence numbers, acknowledgements provide
reliability - guarantee that packet loss or duplication will be
detected - packets arrive in the order they were sent
- Buffers, flow control algorithm guarantee
transmission rate appropriate to both sender and
receiver - Destination address
- Characteristics of connection (e.g., out-of-band
messages) - Transmission Control Protocol (TCP) is
connection-oriented. - Problem Overhead of setting up taking down
connection.
5Hypertext Transfer Protocol (HTTP)
- A high level protocol built on top of a TCP
connection for exchanging messages (with
arbitrary content) - Each (request) message from client to server is
followed by a (response) message from server to
client. - Facilitates remote invocation of methods on the
server. - Web A set of client and server processes on the
Internet that communicate via HTTP.
6Protocol Stack
HTTP
TCP
Added features to support client interactions
(reliability flow control, ..)
Network Level Protocol
End-to-end protocol
Link Level Protocol
Protocol for tranmitting packets between
neighboring nodes
7Clients and Servers
- Client browser capable of displaying HTML pages.
- Web Server stores pages for distribution to
clients. - Pages identified by Uniform Resource Locator
(URL). - ltprotocolgt protocol to be used to communicate
with host. - Example - http, ftp
- lthost_namegt Directory server translates this
into the hosts internet address - Example www.cs.sunysb.edu becomes
155.233.123.532 - ltfile_namegt name of file on host.
ltprotocolgt//lthost_namegt/ltfile_namegt
8HTTP Request Format
Start line ltmethodgt ltURLgt
ltprotocol_versiongt CrLf Followed by
ltheadergt Followed by CrLf Followed by
ltdatagt ltmethodgt GET HEAD POST PUT
. ltprotocol_versiongt HTTP/1.1 .
there can be several header lines
9Request Methods
- GET response body contains data identified by
argument URL - HEAD response header describes data identified
by argument URL (no response body) - Use has page changed since last fetched?
- PUT request body contains page to be stored at
argument URL
10Request Methods
- DELETE delete data at argument URL
- POST request body contains a new object to be
placed subordinate to object at argument URL - Use adding file to directory named by URL
- Use information entered by user on displayed
form - Others .
11HTTP Request Format
ltheadergt ltfield_namegt ltvaluegt
CrLf ltfield_namegt From --
senders e-mail address Accept --
acceptable response formats User-Agent
-- identifies requestors program SOAPAction
-- identifies SOAP processor to
receive message (if data is a SOAP message)
If-Modified-Since -- send document only if
modified since ltvaluegt (used with
GET) Content-Type -- type of data
(application/soapxml
for SOAP) Host
-- destination host ltdatagt ASCII text
(default)
12Simple Client / Server Interaction I
- 1. User supplies URL (clicks on link)
- http//yourbusiness.com/items/printers.h
tml - 2. Browser translates lthost_namegt
(yourbusiness.com) - to host_internet_address (using name server)
- 3. Browser assumes a port number of 80 for http
(if no - port is explicitly provided as part of
lthost_namegt ) - Program at port 80 interprets http headers
13Simple Client / Server Interaction I
- 4. Browser sets up TCP connection to
- yourbusiness.com at
- (host internet address, 80)
- 5. Browser sends http message
- GET items/printers.html HTTP/1.0
- over connection
14HTTP Response
Status line ltHTTP_versiongt ltstatus_codegt
ltreason_linegt CrLf Followed by lt header
gt Followed by ltdatagt
15HTTP Response
ltstatus_codegt 3 digits Ex 2xx -- success
4xx -- bad request from client 5xx
-- server failed to fulfill valid
request ltreason_linegt explanation for human
reader ltheadergt ltfield_namegt ltvaluegt
CrLf ltfield_namegt Allowed -- methods
supported by URL Date -- creation date
for response Expires -- expiration date
for data Last-Modified -- creation date
for object Content-Length Content-Type
.
16Simple Client/Server Interaction I
- 6. Server sends response message with requested
html page to browser - 7. Server releases TCP connection (stateless)
- 8. Browser receives page and displays it
HTTP/1.0 200 Document follows Date
ltdategt Content-Type text/html Content-Length
integer Expires date html document
items/printers.html goes here
17Simple Client/Server Interaction II
- 1. Page displayed by browser is a form with tag
- ltFORM ACTIONhttp//yourbusiness.com/servlets/pl
aceorder - METHODgt
- 2. Client fills input boxes
- 3. If METHODGET, client sets up connection to
yourbusiness.com and sends http request -
- Values in input boxes encoded as suffix.
Since ACTION - designates a servlet, server invokes
placeorder
GET /servlets/placeorder?name1value1name2value2
HTTP/1.0
18Simple Client / Server Interaction II
- 4. If METHODPOST, client sends http request
- invoking POST to yourbusiness.com data
- contains values in input boxes.
POST /servlets/placeorder HTTP/1.0 Content-Type
text/. Content-Length 54321 PrinterHP660
NameArtBernstein
19HyperText Transfer Protocol (HTTP 1.1)
- 1. Client sets up TCP connection to server named
in URL - 2. Client sends a request
- 3. Client receives a response
- 4. If (server has not disconnected) goto 2 else
goto 1 - - Only actively used connections are maintained
20SOAP
21What is SOAP?
- The de facto standard for Web Service
communication that provides support for - Remote procedure call (RPC) to invoke methods on
servers - Messaging to exchange documents
- Extensibility
- Error handling
- Flexible data encoding
- Binding to a variety of transports (e.g., SOAP,
SMTP) - We will discuss Version 1.2
22HTTP Binding
- A SOAP message must be carried by some transport
protocol - HTTP is frequently used for this purpose
- Message is the data part of a request invoking
POST
POST /fareService/getFareOp HTTP/1.1 Host
www.SlowHawk.com Content-Type
application/soapxml Content-Length
xxx SOAPAction yyy lt! the SOAP message goes
here ?
23SOAP and XML
- Since XML is language and platform independent,
it is the lingua franca for the exchange of
information in a heterogeneous distributed
system. - SOAP supports the transmission of arbitrary XML
documents - For RPC, SOAP provides a message format for
invoking a procedure and returning results in XML
24SOAP Message
SOAP Envelope
SOAP Header
Header Block
optional
Header Block
SOAP Body
Message Body
required
25SOAP Envelope
ltsEnvelope xmlnsshttp//www.w3.org/2003/05/soa
p-envelopegt ltsHeadergt lt!-- header
blocks go here --gt lt/sHeadergt ltsBodygt
lt!-- an XML document goes here --gt
lt/sBodygt lt/sEnvelopegt
http//www.w3.org/2003/05/soap-envelope
identifies a name space that defines the
structure of a SOAP message
26Using SOAP
- For document exchange, the XML document being
exchanged is nested directly in SOAP envelope. - Referred to as document-style SOAP
- Conversational mode of message exchange
- For RPC, SOAP defines the format of the body of
messages to be used for invocation and response. - Referred to as RPC-style SOAP
- Uses a request-response pattern
- Parameters are passed by value/result
27RPC Request Message
Client invocation of procedure public Float
getQuoteOp(String symbol) generates SOAP request
message
ltsEnvelope xmlnsshttp//www.w3.org/2003/05/soa
p-envelope xmlnsxsdhttp//www.w3.org/20
01/XMLSchema xmlnsxsihttp//www.w3.org/
2001/XMLSchema-instancegt ltsBodygt ltngetQuot
eOp xmlnsnhttp//www.shearson.com/quoteService
gt ltnsymbol xsitypexsdstringgt IBM lt/n
symbolgt lt/ngetQuoteOpgt lt/sBodygt lt/sEnvelope
gt
28RPC Response Message
ltsEnvelope xmlnsshttp//www.w3.org/2003/05/soa
p-envelope xmlnsxsdhttp//www.w3.org/20
01/XMLSchema xmlnsxsihttp//www.w3.org/
2001/XMLSchema-instancegt ltsBodygt ltngetQuo
teOpResponse xmlnsnhttp//www.shears
on.com/quoteServicegt ltnvalue
xsitypexsdfloatgt 30.45 lt/nvaluegt lt/ng
etQuoteOpResponsegt lt/sBodygt lt/sEnvelopegt
29RPC Request/Response Messages
- Conventions
- Name of the request structure is same as method
name. - Name of response structure is same as method name
concatenated with Response - Name and order of in and in/out parameters in
request structure same as name and order in
signature - Value of method (if returned) is first child
element of response structure out and in/out
parameters follow, their name and order same as
name and order in signature
30Data Encoding
- Problem SOAP provides a language/platform
independent mechanism for invoking remote
procedures - Argument values are carried in an XML document
- Caller and callee may use different
representations of the same types (e.g., Java, C) - A mechanism is needed for mapping from callers
format to XML syntax and from XML syntax to
callees format (referred to as
serialization/deserialization) - Example mapping a Java array to XML syntax
31Serialization
- Serialization is simple for simple types
(integer, string, float,) since they correspond
to XML Schema types. - Translate from binary to ASCII using XML schema
specified format - Serialization not so simple for complex types
- Ex What tags will be used for an array? Will it
be stored by rows or by columns? How will a
sparse array be sent?
32Encoding Style
- encodingStyle attribute used to identify the
serialization rules to encode the data contents
of an element - An arbitrary set of rules can be used
- SOAP defines its own set of rules
- Message is referred to as RPC/encoded
- RPC refers to the format of the message as a
whole - Encoded refers to the fact that argument values
have been represented using the rule set
specified in the encoding style attribute
33SOAP Encoding Style
- SOAP defines its own graphical data model for
describing complex types and rules for
transforming instances of the model into
serialized ASCII strings - Vendors provide serializers (and deserializers)
which maps each local type to an instance of the
model and then transforms the local
representation to the encoded data using the SOAP
rules
34Data Encoding
ltsEnvelope xmlnsshttp//www.w3.org/2003/05/soa
p-envelope xmlnsxsdhttp//www.w3.org/20
01/XMLSchema xmlnsxsihttp//www.w3.org/
2001/XMLSchema-instancegt ltsBodygt ltngetQuot
eOp xmlnsnhttp//www.shearson.com/quoteService
sencodingStylehttp//www.w3.org/2003/05/soap
-encodinggt ltnsymbol xsitypexsdstringgt
IBM lt/nsymbolgt lt/ngetQuoteOpgt
lt/sBodygt lt/sEnvelopegt
35SOAP Extensibility
- A SOAP message goes from client to server to
advance some application related cause. - It is often the case that some orthogonal issues
related to the message must be handled - Security encryption, authentication,
authorization - Transaction management
- Tracing
- Logging
36Intermediaries
intermediary
intermediary
client
server
- To support scalability and decentralization,
these issues need not be handled by the server. - Intermediaries between client and server are used
- Intermediaries perform orthogonal services as the
message passes along a route
37Example
purchasing server
Proxy/ gateway
client
accounting server
inventory server
Message addressed to Proxy. Contains target dept
(purchasing), client name, password, and
request body. Proxy performs authentication.
Message addressed to target dept. Contains
authenticated Id and request body. Target
department services the request.
38Requirements
- Information directed to each intermediary and to
final destination kept separate - Intermediaries can be easily added/deleted, route
changed - SOAP does not specify how routing is to be done
- It is up to each node along the chain to know
where to send the message next - Information carried in the message may direct
routing
39Header
- SOAP envelope defines an optional header
containing an arbitrary number of header blocks.
Each block - Has an optional role and should be processed by
an intermediary that can perform that role - Can have its own namespace declaration
- Eliminates the possibility of interference
between groups that independently design headers.
40Example Message Sent by Client
POST /purchasing/retailSale HTTP/1.1
-- method invoked at final destination Host
proxy.yourcompany.com
-- initial destination intermediary
. ltsEnvelope xmlnss.gt
ltsHeadergt lttdtargetdept xmlnstd.
srolecompany-proxy.com -- identifies
intermediary smustUnderstandtruegt
-- this header better be processed purchas
ing -- identifies next
node lt/tdtargetdeptgt ltauthauthinfo.
srolecompany-proxy.com -- identifies
intermediary smustUnderstandtrue gt
-- this header better be processed ltauthn
amegt madonna lt/authnamegt ltauthpasswdgt xxxxxx
lt/authpasswdgt lt/authauthinfogt lt/Headergt
ltsBodygt lt/sBodygt lt/sEnvelopegt
41Processing Model
- An intermediary has an assigned set of roles
- On receiving a message, it identifies the blocks
whose role attribute matches an element of its
set (or has value next) - A block without a role attribute is targeted for
final destination - The intermediary
- can modify/delete its block
- can insert new blocks
- should retarget the message to the next
destination - can do anything (frowned upon)
42Must Understand
- An intermediary can choose to ignore a block
directed to it - If mustUnderstand attribute has value true
intermediary must process the block or else abort
the message and return a fault message
43Example Message Sent by Proxy
POST /purchasing/retailSale HTTP/1.1
-- method invoked at destination Host
purchasing.yourcompany.com
-- initial intermediary . ltsEnvelope
xmlnss.gt ltsHeadergt ltccClientCredentials
xmlnscc. smustUnderstandtrue gt
-- this block better be processed by
-- destination (no role
specified) ltccclientIdgt 122334
lt/ccclientIdgt lt/ ccClientCredentials gt
lt/Headergt ltsBodygt lt/sBodygt
-- same body lt/sEnvelopegt
44Example Message Sent by Proxy
- Proxy has deleted the two headers
- Verified that user is valid using ltnamegt and
ltpasswdgt and determined Id - Retargeted message to final destination using
lttargetdeptgt - Proxy has inserted a new header containing Id
- Final destination uses Id to determine
authorization
45WS-Addressing
- Problem As described up to this point
destination address (including target SOAP
processor) is not included in SOAP message - This information is contained in transport header
(e.g., SOAPAction header in HTTP) - Information has to be supplied separately to the
transport and the mechanism for doing this is
different for different transports - SOAP is not transport-neutral
46WS-Addressing
- Solution Include the information in SOAP header
blocks. - WS-Addressing is defined for this purpose
- ltwsaTogt - destination URL
- ltwsaActiongt - message intent (analogous to
SOAPAction) - ltwsaMessageIDgt - unique Id
- ltwsaReplyTogt - address for reply
- ltwsaRelatesTogt - Id of another message
- .
47WS-Addressing
- The type EndpointReferenceType is defined to
carry references to endpoints (e.g., value of
ReplyTo) - Contains destination address as well as
additional information that might be needed to
send a message to that address - Identity of WSDL elements describing destination
(port type, service,..) - Policy information (e.g., should message be
encrypted)
48SOAP Faults
- SOAP provides a message format for communicating
information about errors containing the following
information - Fault category identifies error (not meant for
human consumption) - VersionMismatch
- MustUnderstand related to headers
- Sender problem with message content
- Receiver error had nothing to do with the
message - human readable explanation
- node at which error occurred (related to
intermediaries) - application specific information about Client
error
49Embedding SOAP in HTTP POST
- For document-style SOAP, the envelope is the body
of an HTTP POST. - The HTTP response message simply acknowledges
receipt of HTTP request messsage - For RPC-style SOAP, the envelope containing the
SOAP request is the body of an HTTP POST the
envelope containing the SOAP response (or fault)
is the body of the corresponding HTTP response.
50Embedding RPC-style SOAP in HTTP
POST /StockQuote HTTP/1.1 Content-Type
text/xml Content-Length .. ltsEnvelope
xmlnsshttp//www.w3.org/2003/05/soap-envelope
xmlnsxsdhttp//www.w3.org/2001/XMLSchema
xmlnsxsihttp//www.w3.org/2001/XMLSche
ma-instancegt ltsBodygt ltngetQuoteOp
xmlnsnhttp//www.shearson.com/quoteService
sencodingStylehttp//www.w3.org/2001/06/soa
p-encodinggt ltnstockSymbol xsitypexsdstring
gt IBM lt/nstockSymbolgt lt/ngetQuoteOpgt
lt/sBodygt lt/sEnvelopegt
51Embedding Soap in HTTP GET
- In some situations the client simply wants to
retrieve an XML document - An HTTP GET request message is sent with no data
(no SOAP content) - Document (actually a SOAP envelope) is returned
as the data in the HTTP response
52Web Services Description Language (WSDL)
53Goals of WSDL
- Describes the formats and protocols of a Web
Service in a standard way - The operations the service supports
- The message(s) needed to invoke the operations
- The binding of the messages to a communication
protocol - The address to which messages should be sent
54WSDL Description
- A Web Service is described at both the abstract
and concrete levels - Abstract Level (corresponds to portType
Description Language) - What are the operations that are supported?
- What messages are needed to invoke the
operations? - Concrete Level
- How are the messages bound to a transport
protocol? - What is the Web address to which the messages
should be sent?
55WSDL Abstract Level
- At the abstract level, obtaining a service is
like executing a method of an object - WSDL defines the following elements
- An portType is like an object it consists of a
set of operations - An operation is like a method it is invoked by
messages - A message is composed of parts
- A part is like a parameter and has an associated
type
56Example
- ltportType name GetQuotePTgt
- ltoperation name getQuoteOpgt
- ltinput message gsgetQuoteOpReq/gt
- ltoutput message gsgetQuoteOpResp
/gt - ltfault name invalidSymbolFault
- message
gsinvalidSymbolFaultMsg/gt - lt/operationgt
- lt!-- other operations go here --gt
- lt/portTypegt
gs is the target namespace of the document
containing this declaration and the message
declarations
57Patterns
- The messages exchanged when an operation is
invoked conform to a pattern - WSDL 1.1 has defined two patterns
- Request/response
- Input sent by requestor, output produced by
service - Requestor might wait for response (e.g., RPC) or
might not - Choice is a function of how operation is used and
would be specified at a higher level - One-way
- Input sent by requestor, no response expected
58 Faults
ltoutput message gsgetQuoteOpResp/gt ltfault
name invalidSymbolFault
message gsinvalidSymbolFaultMsg/gt
- Request/response pattern allows a fault message
to replace the output message if server detects a
fault - One-way pattern does not allow fault message
59Example Message Definitions
- ltmessage name getQuoteOpReqgt
- ltpart name stockSymbol type
xsdstring/gt - lt/messagegt
- ltmessage name getQuoteOpRespgt
- ltpart name stockSymbol type
xsdstring/gt - ltpart name QuoteValue type
xsdfloat/gt - lt/messagegt
- ltmessage name invalidSymbolFaultMsggt
- ltpart name faultInfo type
gsfaultType/gt - lt/messagegt
60Parts of a Message
- A message can have many parts
- Each part can be bound to a different position
within the physical message sent by the transport - With SOAP parts can be distributed over body and
header blocks - Each part can have a simple or complex type
defined in an XML schema
61Example
- ltschemagt
- ltcomplexType name faultTypegt
- ltsequencegt
- ltelement name faultCode type
string/gt - ltelement name faultDetail type
string - minOccurs 0 maxOccurs 1/gt
- lt/sequencegt
- lt/complexTypegt
- lt/schemagt
62Concrete Level
- The concrete level defines how portTypes and
operations are bound to transports and addresses - A given portType can be bound to several
different transports and addresses - A Web Service might support a portType using
several different transports - For example, the operations can be invoked using
SOAP over either HTTP or SMTP - The same portType might be supported by several
different Web Services using the same or
different transports - In all of these cases, semantically identical
service should be provided at each address
63Concrete Level
- At the concrete level, WSDL defines the following
elements - A binding describes how the messages of a
portType are mapped to the messages of a
particular transport - An port maps a binding to a Web address
- A service is a collection of ports that host
related portTypes
64Example Service and port
identifies binding
- ltservice name GetQuoteServicegt
- ltport name GetQuoteRPC
bindinggqGetQuoteSOAPBindinggt - ltsoapaddress location
http//www.shearson.com/quoteservice/gt - lt/portgt
- lt!Other ports go here --gt
- lt/servicegt
65WSDL Extensibility
- A binding maps a portType to a particular
transport - It must be capable of targeting a variety of
transports - Each transport has its own idiosynchrosies
- WSDL is extended by introducing a different
namespace for each transport
ltdefinitions xmlnshttp//schemas.xmlsoap.o
rg/wsdl/ xmlnsxsdhttp//www.w3.org/2001/
XMLSchema xmlnssoaphttp//schemas.xmlsoap
.org/wsdl/soap/ targetNamespacehttp//www.s
hearson.com/quoteservicegt lt!-- WSDL
declarations go here --gt lt/definitionsgt
introduce SOAP namespace
66Example RPC/encoded SOAP Binding
identifies portType
- ltbinding name GetQuoteSOAPBinding type
tnsGetQuotePTgt - ltsoapbinding style rpc
- transport http//schemas.xmlsoap.
org/soap/http//gt - ltoperation name getQuoteOpgt
- ltinputgt
- ltsoapbody
- use encoded
- namespace
http//www.shearson.com/quoteservice - encodingStyle
http//schemas.xmlsoap.org/soap/encoding/gt - lt/inputgt
- Continued on next slide
rpc style msg
for tags used in messsage
SOAP extensions
encode parameters
encoding rules
67Binding Example - Continued
- ltoutputgt
- ltsoapbody
- use encoded
- namespace
http//www.shearson.com/quoteservice - encodingStyle
http//schemas.xmlsoap.org/soap/encoding//gt - lt/outputgt
- lt/operationgt
- lt!-- other operations go here
--gt - lt/bindinggt
68RPC/encoded Message
ltsEnvelope xmlnsshttp//www.w3.org/2003/05/soa
p-envelope xmlnsxsdhttp//www.w3.org/20
01/XMLSchema xmlnsxsihttp//www.w3.org/
2001/XMLSchema-instancegt ltsBodygt ltngetQuot
eOp xmlnsnhttp//www.shearson.com/quoteService
gt ltnstockSymbol xsitypexsdstringgt IBM
lt/nstockSymbolgt lt/ngetQuoteOpgt
lt/sBodygt lt/sEnvelopegt
69Encoding
- Problem Serializer serializes arguments (parts)
in accordance with rules specified by
encodingStyle attribute - Receiver can deserialize arguments since style is
specified in the message - But message has a declared type
- How can we be sure that the rules produce an
instance of the type? - In fact they might not!
70Example Encoding Style
- Suppose there are n arguments of the same type.
- Serializer might produce a message containing n
instances of the type. - But suppose in a particular invocation all
arguments have same value. - Serializer might produce a message containing n
pointers to a single instance of the value. - Then the value of each argument (a pointer) is
not an instance of the type!
71Encoded Vs. Literal
- If useencoded, arguments are encoded in
accordance with the specified encoding style - If useliteral, arguments are instances of part
types specified in the message declaration - Yields two distinct styles for invoking a remote
procedure - rpc/encoded
- rpc/literal
72Example RPC/literal SOAP Binding
identifies portType
- ltbinding name GetQuoteSOAPBinding type
tnsGetQuotePTgt - ltsoapbinding style rpc
- transport http//schemas.xmlsoap.
org/soap/http//gt - ltoperation name getQuoteOpgt
- ltinputgt
- ltsoapbody
- use literal
- namespace
http//www.shearson.com/quoteservice/gt - lt/inputgt
- ltoutputgt . lt/outputgt
- lt/operationgt
- lt/bindinggt
rpc style msg
dont encode parameters
73RPC/literal SOAP Binding
lttypesgt ltschemagt ltcomplexType
namecomptypgt lt/complexTypegt
ltschemagt lt/typesgt ltmessage namemsggt ltpart
namepart1 typecomptyp /gt lt/messagegt ltsoap
Envelopegt ltsoapBodygt ltnmyProc
xmlnsngt ltnpart1gt
instance of comptyp lt/npart1gt
lt/nmyProcgt lt/soapBodygt lt/soapEnvelopegt
74RPC/encoded and RPC/literal
- RPC style specified for both bindings
- There is no schema describing the (entire)
message body - Child of body element uses name of procedure
- Each grandchild corresponds to a parameter and
uses parameter name - Might be a grandchild for result returned
- Hence, validation is not possible
75Sending Documents
- Increasingly, Web communication is
- Asynchronous
- Web Services are loosely coupled (as opposed to
tightly coupled, object-oriented systems that are
developed in a more integrated fashion and are
more oriented towards rpc) - More appropriate for delay prone/failure prone
environments - Messages contain XML documents (instead of
procedure arguments) - A wide variety of communication patterns (as
opposed to simply request/response) are useful
76Example - Document Style Messaging
ltmessage name sendInvoiceMsggt ltpart name
invoice type invinvoiceType/gt lt/messagegt
ltportType name invoicePTgt ltoperation name
sendInvoiceOpgt ltinput message
invsendInvoiceMsg/gt lt/operationgt lt/portTypegt
one-way pattern
77Example (cont)
SOAP body contains XML documents
ltbinding name sendInvBinding type
inginvoicePTgt ltsoapbinding style
document transport
http//schemas.xmlsoap.org/soap/http/gt
ltoperation name invsendInvoiceOpgt
ltinputgt ltsoapbody use
literal namespace
http//www.invoicesource.com/invoice/gt
lt/inputgt lt/operationgt lt/bindinggt
body is an instance of part type
78Document/literal SOAP Binding
Alternative 1 one part specified by a type
lttypesgt ltschemagt ltcomplexType
namecomptypgt lt/complexTypegt
ltschemagt lt/typesgt ltmessage namemsggt ltpart
namepart1 typencomptyp /gt lt/messagegt ltsoa
pEnvelopegt ltsoapBodygt instance of
comptyp lt/soapBodygt lt/soapEnvelopegt
n is target namespace of this document
message can have only one part in this case since
the schema of the body can have only one type
specification
79Document/literal SOAP Binding
Alternative 2 part specified by an element
lttypesgt ltschemagt ltelement nameelem
typencomptyp /gt ltcomplexType
namecomptypgt lt/complexTypegt
ltschemagt lt/typesgt ltmessage namemsggt ltpart
namepart1 elementnelem /gt lt/messagegt ltsoa
pEnvelopegt ltsoapBodygt ltnelem
xmlns target ns of WSDL doc gt
instance of comptyp
lt/nelemgt lt/soapBodygt lt/soapEnvelopegt
Part is identified as an element. An instance
of element is a child of body, named with
elements name, typed with elements type
80Sending Multiple Documents
ltelement namefirstInvoice typeinvinvoiceTyp
e /gt ltelement namesecondInvoice
typeinvinvoiceType /gt ltcomplexType
nameinvoiceTypegt lt!-- the complex type
definition goes here --gt lt/complexTypegt ltmessage
name sendInvoiceMsggt ltpart name
invoice1 element invfirstInvoice /gt
ltpart name invoice2 element
invsecondInvoice /gt lt/messagegt
element specification must be used since message
has multiple parts
ltsoapBodygt ltinvfirstInvoicegt lt!--
instance of invoiceType goes here --gt
lt/invfirstInvoicegt ltinvsecondInvoicegt
lt!-- instance of invoiceType goes here --gt
lt/invsecondInvoicegt lt/soapBodygt
81Sending Messages By Email Simple Mail Transfer
Prototol
- ltservice name GetQuoteSMTPServicegt
- ltport name GetQuoteSMTP
- bindinggqGetQuoteSMTPBin
ding/gt - ltsoapaddress
- location
mailtostockquote_at_shearson.com/gt - lt/portgt
- lt/servicegt
82Mail Example (continued)
- ltbinding name GetQuoteSMTPBinding
- type tnsGetQuotePTgt
- ltsoapbinding style document
- transporthttp//schemas.xmlsoap
.org/soap/smtp /gt - ltoperation name getQuoteOpgt
- ltinputgt
- ltsoapbody useliteral/gt
- lt/inputgt
- ltoutputgt
- ltsoapbody useliteral/gt
- lt/outputgt
- lt/operationgt
- lt/bindinggt
83Complete WSDL Document
ltdefinitions targetNamespace. xmlns
other namespaces gt lttypesgt lt!
specification of XML Schema types used in this
document --gt lt/typesgt ltmesssagegt
lt/messsagegt lt! specification of other
messages goes here--gt ltportTypegt
lt/portTypegt lt! specification of other
portTypes goes here--gt ltbindinggt
lt/bindinggt lt! specification of other
bindings goes here--gt ltservicegt
ltportgt lt/portgt lt! specification of
other ports goes here--gt lt/servicegt
lt!-- specification of other services goes here
--gt lt/definitionsgt
84What WSDL Cannot Do
- WSDL describes how each operation can be invoked
- E.g., getQuoteOp
- Many services require a sequence of operations
- Send this message, receive that message, if this
happens send this other message to another port,
etc - The sequence cannot be described in WSDL
- BPEL describes the logic of a Web Service
- How it is impemented
- How it communicates with other busienss processes
- Sometimes called an orchestration language
85Business Process Execution Language for Web
Services (BPEL4WS)
Version 1.1
86BPEL vs. WSDL
- WSDL supports a stateless model which describes
operations supported by web servers - One or two messages needed for client/server
communication - No mechanism for describing state between
operations - A business process (BP) typically characterized
by long-running, statefull sequence of operations
with one or more web services (business partners).
87Simple Example Ordering Stationery
- cobegin
- invoke Staples.StationeryQuote(staples-quot
e) - invoke Office-Max.StationeryQuote
Service(max-quote) - coend
- if staples-quote lt max-quote
- invoke Staples.StationeryPurchase
- else
- invoke Office-Max.StationeryPurchase
-
state
88New Issues
- A language for business processes
- Must be able to communicate with other Web
Services - Must be able to access and modify data received
in messages - Use XPath to extract information from messages
- Must have control constructs
- sequence, switch (if), flow (concurrency), while,
link (synchronize concurrent processes), invoke,
etc - Must be able to handle faults
89Example (BPEL)
- ltsequencegt
- ltflowgt
- ltinvoke partnerLinkStaples
portTypestaplesPurchasePt - operationrequestQuote
inputVariablestationeryReq - outputVariablestaplesStati
oneryQuotegt - lt/invokegt
- ltinvoke partnerLinkOfficeMax
portTypeofficeMQuotePT - operationrequestQuote
inputVariablestationeryReq - outputvariableofficeMStati
oneryQuotegt - lt/invokegt
- lt/flowgt
-
- .. Continued
on next slide ..
90Example (BPEL)
- ltswitchgt
- ltcase conditionbpwsgetVariableProperty(sta
plesStationeryQuote, quote) - lt
bpwsgetVariableProperty(officeMStationeryQuote,
quote) /gt - ltinvoke partnerLinkStaples
portTypestaplesQuotePt - operationpurchStation
ery inputVariablestationeryPurch - outputVariablestation
eryRespgt - lt/invokegt
- lt/case
- ltotherwisegt
- ltinvoke partnerLinkOffice Max
portTypeofficeMQuotePT - operationpurchStation
ery inputVariablestationeryPurch - outputVariablestation
eryRespgt - lt/invokegt
- lt/otherwisegt
- lt/switchgt
- lt/sequencegt
91Business Process (BP)
- A BP consists of both internal computations and
invocations of operations exported by Web service
partners - The operations it exports constitute its
interface to its partners - The sequence of invocations it executes is
referred to as a protocol and - is data dependent
- responds to exceptional conditions
92Abstract Vs. Executable BPs
- Executable BP complete description of BP
(including all computations) - Abstract BP contains only externally visible
(communication related) behavior of BP - Not executable
- Intention Internal decision making algorithm and
data manipulation not described (although this is
not enforced) - Languages for describing abstract and executable
BPs share a common core, but differ primarily in
data handling capabilities - BPEL4WS is used to specify both abstract and
executable BPs
93Executable BPs
- BPEL is sufficient for describing a complete
(executable) BP that - Relies on Web services and XML data
- Is portable (platform independent)
- Executable BP is a complete specification of the
Web service - Actual implementation, however, might not use
BPEL, - Abstract BP specifies external interface and can
be exported for use by business partners
94Abstract BP
- Unfolding of protocol related portion of BP
- depends on properties - a subset of the data
contained in messages - Ex. Message invoking getQuoteRequest might have
parts instrumentType (with value stock or bond)
and symbol (which identifies a particular
instrument of that type) - instrumentType will be a property if it affects
the course of the protocol - symbol will not if it does not affect the course
of the protocol - Only properties are visible to abstract BP
95Abstract Vs Executable BP
- Internal computation of executable BP not
included in abstract BP - If assignment is to a variable that is not a
property, it is eliminated from abstract process - Ex. Address data might not affect the protocol
- If assignment is to a variable that is a
property, it (generally) affects the protocol - Ex. Value of bidPrice might affect protocol
- if (bidPricegt1000) invoke webService1 else invoke
webService2 - bidPrice will be a property, but its value is
computed by an internal algorithm - The computation that produces the new value is
generally not relevant to the protocol
96Abstract BP Non-determinism
- Description of abstract BP allows assignment of
non-deterministic values to properties to model
this - Abstract and executable BPs differ in data
handling ability - Executable can explicitly manipulate all data
- Abstract can access only properties and can
assign non-deterministic values to them - Executable cannot assign non-deterministic values
to anything
97Abstract BP Non-determinism
computation that assigns a value to part x
non-deterministic assignment to property
x? (alias of x)
switch(x)
switch(x? )
Abstract BP
Executable BP
98Communication Client Side
- Invoking an operation of a portType (specified in
WSDL) exported by server - Client assigns message to operations input
variable - Client executes invoke on operation
- Asynchronous (one-way WSDL pattern)
- Client resumes execution immediately
- Synchronous (request/response WSDL pattern)
- Client waits for response and then resumes
execution - Synchronization imposed by BPEL
- Client can access response message in operations
output variable
99Communication Client Side
- Receiving an invocation of an operation exported
by client - Client executes receive on operation
- Client waits for message
- Client can access message in variable associated
with operation and resume execution - Ex an asynchronous response to a prior
invocation on a callback portType
100Communication Client Side
client
server invoke invoke invoke receive
(synchronous invoke)
client waits
(asynchronous invoke)
server exports portType
client continues
(asynchronous invoke)
problem how do you associate request
with response?
(asynchronous invoke)
client exports (callback) operation
101Communication Server Side
- Accepting an operation invocation on an
(exported) portType (specified in WSDL) - Server executes receive on operation and waits
- Responding to a synchronous operation invocation
- Server executes reply on operation (rpc)
- Invoking a clients exported (callback) operation
- Server executes invoke on operation
102Communication Server Side
client
server invoke
(synchronous invoke)
receive
reply
(asynchronous invoke)
receive
server exports portType
invoke
(asynchronous invoke)
receive
invoke
(asynchronous invoke)
receive
invoke
client exports (callback) portType
103Example Purchase Order (PO) Service
receive purchase order
concurrency
sequencing
initiate price calculation
decide on shipper
initiate production scheduling
complete price calculation
arrange logistics
complete production scheduling
synchronization
invoice processing, reply
104PO Service
PO Service
receive
synchronous invocation
POMsg
Body of PO Service
customer
operation sendPurchOr on portType purchOrPT
InvMsg
reply
105PO Service Interface (WSDL)
ltdefinitions targetNamespace.
xmlnshttp//schemas.smlsoap.org/wsdl/ gt
ltmessage namePOMsggt ltpart namecustInfo
typesnscustInfo/gt ltpart namepurchOr
typesnspurchOr/gt lt/messagegt ltmessage
nameInvMsggt ltpart nameIVC
typesnsInvoice/gt lt/messagegt .. ltportType
namepurchOrPTgt ltoperation
namesendPurchOrgt ltinput
messageposPOMsg/gt -- arguments supplied
ltouput messageposInvMsg/gt -- response
lt/operationgt lt/portTypegt ..
portType exported by PO Service
prefix for target namespace in this document
lt/definitionsgt
106Variables (BPEL)
- Variables maintain the state of a BP
- Used to store messages that have been sent or
received or for local storage (no message
involved) - Has an associated type
- Can be a message type
- Can be an XML simple type
- Can be an XML schema element (which might have a
complex type) - Has an associated scope
ltvariable namePO messageTypelnsPOMsg/gt
lns is prefix in BPEL document for the WSDL
document
107Partner Link Type (WSDL)
ltpartnerLinkTypegt describes the way two BPs
interact - names a portType that must be
declared in each - associates ltrolegt with
each end of the interaction
Not a process (allows actual partner to be
specified dynamically)
WSDL extension for BPEL
ltplnkpartnerLinkType namepurchLTgt
ltplnkrole namepurchServicegt
ltplnkportType namepospurchOrPT/gt
lt/plnkrolegt lt/plnkpartnerLinkTypegt
partnerLinkType is a unit of collaboration
Only one role (in this case) since only POService
needs to provide an portType
108Partner Link Type (WSDL)
ltplnkpartnerLinkType nameinvoicingLTgt
ltplnkrole nameinvoiceServicegt
ltplnkportType nameposcomputePricePT/gt
lt/plnkrolegt ltplnkrole nameinvoiceRequester
gt ltplnkportType nameposinvoiceCallbackPT
/gt lt/plnkpartnerLinkTypegt
description of a possible relationship between
two BPs
BP playing role of invoice requester
BP playing role of invoice service
invoiceCallbackPT
computePricePT
109Partner Link (BPEL)
Connection to another BP described by a
partner link ltpartnerLinkgt construct in BPEL
names a process and associates it with a
role in that link.
partner specification in PO service
name of partnerLink
prefix lns refers to WSDL document
ltpartnerLinksgt ltpartnerLink namepurchLink
partnerLinkTypelnspurchLT
myRolepurchService/gt lt!-- other
partnerLinks go here --gt lt/partnerLinksgt
hence PO service must provide purchOrPT
110Partner (BPEL)
- A BP might interact with another BP called a
partner - through several partnerLinks - Need a mechanism that asserts that the same BP is
at the other end of a set of partnerLinks - Ex BPs might support getFarePT and
purchaseTicketPT an acceptable partner is one
that supports both
ltpartnersgt ltpartner nameticketVendorgt
ltpartnerLink namexxxx/gt lt!-- supports
getFarePT --gt ltpartnerLink nameyyyy/gt
lt!-- supports purchaseTicketPT --gt
lt/partnergt lt/partnersgt
111Process Name
- Each BP is assigned a name in the ltprocessgt tag
ltprocess namecustomer
namespace declarations query
language (default XPath)
expression language (default XPath) gt
declarations and process body lt/processgt ltproce
ss namepurchOrProcess
similarly gt declarations and body of
PO service lt/processgt
112Linkage Customerto PO Service
plnk prefix in WSDL doc refers to
WSDL extension pos target ns of WSDL doc lns
prefix in PO Service refers to WSDL
doc cns prefix in customer refers to
WSDL doc
ltplnkpartnerLinkType namepurchLTgt
ltplnkrole namepurchServicegt
ltplnkportType namepospurchOrPT/gt
lt/plnkrolegt lt/plnkpartnerLinkTypegt ltpartnerLink
namelinkToPurch
partnerLinkTypecnspurchLT
partnerRolepurchService/gt ltpartnerLink
namepurchLink partnerLinkTypeln
spurchLT myRolepurchService/gt
WSDL inter- face exported by PO Service
partner specification in customer process
partner specification in PO Service
113Partners
In general - A partnerLinktype is not
specific to a particular BP it is a
global, bilateral (WSDL) description of the
interaction between two BPs. - A
partnerLink declaration (BPEL) describes how the
local BP interacts with other BPs
through a
partnerLinktype.
ltpartnerLinksgt ltpartnerLink nameinvoiceProvid
er partnerLinkTypelnsinvoice
LT myRoleinvoiceRequester
partnerRoleinvoiceServices/gt lt/
partnerLinksgt
114PO Service (BPEL)
ltvariablesgt ltvariable namePO
messageTypelnsPOMsg/gt ltvariable
nameInvoice messageTypelnsInvMsg/gt lt/variab
lesgt ltsequencegt ltreceive partnerLinkpurchLi
nk portTypelnspurchOrPT
operationsendPurchOr variablePO/gt
lt/receivegt ltflowgt . concurrent body.
lt/flowgt ltreply partnerLinkpurchLink
portTypelnspurchOrPT
operationsendPurchOr variableInvoice/gt lt/se
quencegt
Both necessary since PO Service might
communicate with several BPs
through the same portType
115Interaction with Shipping Provider
PO service
operation requestShipping on portType shippingPT
decide on shipper (invoke)
shipReqMsg
Shipping service
shipInfoMsg
scheduleMsg
arrange logisitics (receive)
operation sendSchedule on port shippingCallbackPT
role shippingService
role shippingRequester
116Handling Shipping (WSDL)
ltportType nameshippingCallbackPTgt
ltoperation namesendSchedulegt ltinput
message/gt lt/operationgt lt/portTypegt ltportTy
pe nameshippingPTgt ltoperation
namerequestShippinggt ltinput
message/gt ltoutput message/gt
lt/operationgt lt/portTypegt
portType exported by PO Service
portType exported by shipping service
117Handling Shipping
ltplnkpartnerLinkType nameshippingLTgt
ltplnkrole nameshippingServicegt
ltplnkportType nameposshippingPT/gt
lt/plnkrolegt ltplnkrole nameshippingRequester
gt ltplnkportType nameposshippingCallBack
PT/gt lt/plnkrolegt lt/plnkpartnerLinkTypegt ltpar
tnerLink nameshippingProvider
partnerLinkTypelnsshippingLT
myRoleshippingRequester
partnerRoleshippingService/gt
WSDL
BPEL (PO service)
118Handling Shipping (BPEL)
contains input message
ltsequencegt ltassigngt ltcopygt
ltfrom variablePO partcustInfo /gt
ltto variableshippingReq
partcustInfo /gt lt/copygt
lt/assigngt ltinvoke partnerLinkshippingProv
ider portTypelnsshippingPT
operationrequestShipping
inputVariableshippingReq
outputVariableshippingInfo gt lt/invokegt
ltreceive
partnerLinkshippingProvider
portTypelnsshippingCallbackPT
operationsendSchedule variableshippingSch
edule/gt lt/sequencegt
119Links (BPEL) Synchronizing Concurrent Activities
w/i a BP
- Production scheduling cannot be completed until
logistics have been arranged
Concurrent sequence activities in flow
data produced by arrange logistics is needed
by complete production scheduling data
communicated through globally shared variable
decide on shipper
initiate production scheduling
arrange logistics
complete production scheduling
link
source
target
120Links
ltflowgt ltlinksgt ltlink nameship-sched/gt
lt/linksgt ltsequencegt
ltassigngt . lt/assigngt ltinvoke
partnerLink .gt lt/invokegt
ltreceive partnerLink .
variableshippingSchedgt ltsource
linkNameship-sched/gt lt/receivegt
lt/sequen