2. What are “Web Services”?
• IBM
– “A Web service is an interface that describes a collection
of operations that are network accessible through
standardized XML messaging”
• Microsoft: XML Web Services
– “.. expose useful functionality to Web users through a
standard Web protocol”
– “.. provide a way to describe their interfaces in enough
detail to allow a user to build a client application to talk
to them”
– “.. are registered so that potential users can find them
easily”
3. Why Web Services?
• From business standpoint
– Integration
• Within an organization
• Between companies
• Allows time/cost efficiencies
– Purchase orders
– Answering inquiries
– Processing shipment requests
• Do this without locking in to a single partner
4. Web Service Architecture
• Service-Oriented Architecture
Service
Registry
Service
Requestor
Service
Provider
Find Publish
Bind
5. Architecture II
• All the technologies are XML based …
Registry
(UDDI)
Service
Requestor
Service
Provider
Find
Publish
Bind
(SOAP)
(SOAP)
(WSDL)
6. XML Leveraging Features
• XML Namespaces
– Collision
• Common XML element names
– Application specific or embedded in message?
– Allows composition of multiple XML documents
• Identifies elements belonging to the same document
type
7. XML Leveraging Features II
• XML Schemas
– Alternative to DTDs for describing document
structure
– Written in XML
• Simple types
• Complex types
– Reusable
• Intended to be used with namespaces
8. SOAP
• Simple Object Access Protocol
• Web service messaging and invocation
• 2nd Generation XML Protocol
– Takes advantage of
• XML Namespaces
• XML Schema
9. First Generation XML Protocol
• Based on XML 1.0
• Example: XML-RPC
– Introduced by Userland in 1998
– Uses HTTP as underlying transport
<methodResponse>
<params>
<param>
<value>
<string>twenty-eight</string>
</value>
</param>
</params>
</methodResponse>
Call Response
<methodCall>
<methodName>NumberToText</methodName>
<params>
<param>
<value><i4>28</i4></value>
</param>
</params>
</methodCall>
10. First Gen. XML Protocol Issues
• Extensibility
– All protocol architects had to agree for changes
– Avoid with namespaces
• Datatyping
– Single DTDs
• Limited in use of XML elements
• Descriptive nature of XML sacrificed
– XML schema is a better solution
11. SOAP History
1998 • Term SOAP coined at Microsoft
1999 • Microsoft works with BizTalk to release SOAP 0.9
• Submitted to IETF
• SOAP 1.0 released in December
2000 • SOAP 1.1 submitted to W3C with IBM
• IBM releases a Java SOAP implementation
• Sun starts work on Web services in J2EE
2001
• SOAP 1.2 released by XML Protocol working group at W3C
Currently, about 80+ SOAP implementations available
including Apple…
12. SOAP Messaging Layers
App API
SOAP, XML Processing
App API
SOAP, XML Processing
SOAP Message SOAP Message
HTTP HTTP
Developer
SOAP Service
Provider
HTTP
Client ProviderView
14. SOAP Envelope
• Root element
• Mandatory
• Does not expose any protocol versions
– Protocol version is the URI of SOAP envelope
namespace
– encodingStyle attribute for complex types
<SOAP-ENV:Envelope
SOAP-ENV:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/
xmlns="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/1999/XMLSchema">
15. SOAP Header
• Optional
• Allows packaging of information orthogonal to
message
– Transactions
• Authentication information
• Account information
• SOAP-ENV:mustUnderstand
16. SOAP-ENV:mustUnderstand
• Attribute for Header element
• Value 0 – skip this element if it doesn’t make
sense
• Value 1 – must fail if it doesn’t make sense
– Ensures recipients be aware of important protocol
extensions
<SOAP-ENV:Header>
<t:client xmlns:t=“Some-URI”
SOAP-ENV:mustUnderstand=“0”>
sacharya@inktomi.com
</t:client>
</SOAP-ENV:Header>
17. SOAP Body
• Can contain arbitrary XML
• Conventions for
– RPCs
– Faults
• Faultcode – lookup string
• Faultstring – human readable string
• Faultactor – where in the message path
• Detail – optional
– Data encoding
18. Data encoding in SOAP
• SOAP provides default encoding schema
– Why reinvent the wheel?
• Simple data types
– Use “xsi:type”
– String, floats etc
• Complex data types
– SOAP arrays
– Structs: compound types
• Data referencing
– Href and id attributes
19. Data encoding in SOAP
• Binary data
– Base64 encoding
• Can roll your own schema
– encodingStyle
– Interoperability issues
21. Other SOAP Protocol Bindings
• HTTPS
– Similar to HTTP
• Use POST
• Return 200 for success
• 500 for failure + SOAP fault
• SOAPAction HTTP header for hint
• MIME media type: text/html
• SMTP
• SOAP messages with Attachments
