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Web Services and Service
Oriented Architecture
Aravind Sriram
Today’s Web
Web designed for application to human interactions
Served very well its purpose:
Information sharing: a distributed content library
Enabled B2C e-commerce
Non-automated B2B interactions
How did it happen?
Built on very few standards
Shallow interaction model: very few assumptions made
about computing platforms
Result was ubiquity
Problems
Involve a whole learning curve
Not based on standardized rules and specifications
Module CORBA Module
A B
CORBA
CORBA
Module
C
Module RMI Module
A B
What’s next?
The Web is everywhere. There is a lot more we can do!
E-marketplaces.
Open, automated B2B e-commerce.
Business process integration on the Web.
Resource sharing, distributed computing.
Current approach is ad-hoc on top of existing standards.
e.g., application-to-application interactions with HTML
forms.
Goal:
enabling systematic application-to-application
interaction on the Web.
Web Services
Provide
Standardized method of communication between
software applications
Distributed components are interfaced
via non-object-specific protocols
Module Module
A B
C++ Java
What is a web service?
W3C Definition:
A Web service is a software application identified by a URI, whose
interfaces and binding are capable of being defined, described and
discovered by XML artefacts and supports direct interactions with
other software applications using XML based messages via internet-
based protocols
Other definitions
“Web services” is an effort to build a distributed computing platform
for the Web.
enabling systematic application-to-application interaction on the
Web.
Designing Web Services
Goals
Enable universal interoperability.
Widespread adoption, ubiquity: fast!
Enable (Internet scale) dynamic binding.
Efficiently support both open (Web) and more constrained
environments.
Requirements
Based on standards. Pervasive support is critical.
Minimal amount of required infrastructure is assumed.
Only a minimal set of standards must be implemented.
Very low level of application integration is expected.
But may be increased in a flexible way.
Focuses on messages and documents, not on APIs.
Web Services Framework
Describe
Expose—Services register in a repository providing
Business information (White pages)
Service information (Yellow pages)
Binding information (Green pages) describing how to connect and
use the services
Invoke—Remote application can invoke service
Respond—When service is invoked, results are returned to the
requester
Manage/Govern – Provided structure and process control
Fundamentals of Web Services
A web service is a programmable component that provides a service and is
accessible over the Internet.
Instance Client
Component Instance Client
Network
Instance Client
Fundamentals of Web Services
Web services stack
Fundamentals of Web Services
Web services stack
Service & Information Layer
Types
Message
Operation
Service Port Type
Implementation
Binding
Port
Web Service Interface
(WSDL) Service
Using WSDL
1. Describe the message interchange formats the service can support
2. WSDL may define where the service is available and what
communications protocol is used to talk to the service.
3. As extended IDL: WSDL allows tools to generate compatible client
and server stubs.
4. Allows industries to define standardized service interfaces.
5. Allows advertisement of service descriptions, enables dynamic
discovery and binding of compatible services.
6. Provides a normalized description of heterogeneous applications.
WSDL Document
<definition>
Abstract interface Logical grouping of operations
(service
interface message
definition) Data description using XML Schema
______________
service
Concrete Actual data structures used to pass
(service binding data
implementation
Definition) endpoint/port
Service Definition = Abstract + Concrete
Service Description = Service Definition + Supplementary Definitions
XML-eXtensible Markup Language
In Web services, a message is an XML document information item as
defined by the XML Information
.
The Information items generally maps to the various features in an
XML document, such as elements, attributes, namespaces, and
comments ….
All the technologies in Web Services are XML based
Messaging
Description Are all in XML
Registry
Why?
Fundamentals of Web Services
Web services stack
Packaging Layer
Simple Object Access Protocol (SOAP) is a lightweight protocol
designed for the exchange of information using XML
Defines a modular packaging model and the encoding
mechanisms for encoding data within modules .
Envelope
Encoding rules
SOAP RPC representation
Fundamentals of Web Services
Web services stack
Protocol Layer
Any of the standard Internet protocols may be used to invoke web
services over the network .
The initial definition focuses specifically on HTTP/1.1 and the
encrypted HTTPS
FTP and SMTP can also be used
Invoking a web service
A client invoking a Web service
Discovery Layer
The Universal Description, Discovery, and Integration protocol, or
UDDI, specifies a protocol for querying and updating a common
directory of Web service information.
UDDI directory approach can be used when Web service information is
stored in well-known locations.
UDDI provides inquiry and publishing API’s
Microsoft, IBM and SAP host the UDDI Business Registry.
Directory entry has three primary parts – the service provider, Web
services offered, and bindings to the implementations.
Dynamically discovered Web services explicitly announce their arrival
and departure from the network.
UDDI Universal Description Discovery
and Integration 3.
1. SW companies, standards
bodies, and programmers
populate the registry with
descriptions of different Marketplaces, search
types of services engines, and business
apps query the registry
to discover services at
2. other companies
• Businesses Business 4.
populate Service
Descriptions
Types
the registry with
descriptions of the
services they Business uses this
support data to facilitate
easier integration
with each other
over the Web
Web Services Pros and Cons
Pros Cons
Global method for describing Emerging technology
and finding Internet–based
Managing and Tracking changes
business services
is a challenge
Packaging and publishing of
applications in a readily Transactions not fully addressed
understood format Multiple, evolving security
New revenue streams through standards
syndication of existing Processing overhead
application as Web Service
Future Vision and Challenges
Technology vendors plan to develop, market, and lend online Web
services to fulfill virtually any business function.
Companies will be able to simply search a public directory of
applications and download those that fit their needs.
Right now we have only tools and standards which are still not matured,
but it’s needless to say that its time to learn and practice some web
services development
Challenges
Example
Google
A great search engine
but what if I want my own GUI?
Google web service
Google offers a web service that performs searches for
you
Why?
clients can build custom GUIs
google.com can make money!
// ask google to search for us...
google = new GoogleSearchService();
result = google.doGoogleSearch("4a8/TvZQFHID0WIWnL1CMmMx0sNqhG8H",
txtSearch.Text, 0, 10, false, "", false, "", "", "");
// display resulting URLs...
foreach (ResultElement re in result.resultElements)
lstURLs.Items.Add(re.URL);
(1) Building a web service
Start by creating a project of type “ASP.NET Web
Service”
A web service is…
One or more objects that respond to web-based
method calls
there is no GUI design to a web service
only raw classes with methods…
public class Service1 : System.Web.Services.WebService
{
.
.
.
}
Example
Looks like C#, but keep in mind these are web-based methods
client could be calling from any platform
parameters passed using XML
public class Service1 : System.Web.Services.WebService
{
[WebMethod]
public int Add(int x, int y)
{
return x + y;
}
[WebMethod]
public string[] Attendees()
{
<<open DB, read attendees into array, return it>>
}
}
(2) Building a client
Start by creating a client…
WinForm, WebForm, console-based, anything you
want!
for fun, let's use VB…
Reference the component
As usual, we need to reference component
this will activate IntelliSense
this will make sure we call it correctly
this will enable underlying XML +
SOAP communication
How?
project references, right-click, Add web reference…
type URL for web service, e.g.
http://localhost/WebService/Service1.asmx
web service class
server name name
Program against component
Treat web service like any other class!
use new to create instances
make method calls
pass parameters
Private Sub Button1_Click(...) Handles Button1.Click
Dim i, j, k As Integer
i = CInt(TextBox1.Text)
j = CInt(TextBox2.Text)
Dim obj As localhost.Service1
obj = New localhost.Service1()
k = obj.Add(i, j)
MessageBox.Show("Sum = " + k.ToString())
End Sub
Underlying execution…
web service
client app
obj
obj.Add(i, j); obj.Add(10, 20);
.asmx
proxy
Web server
<Add>
<n1>10</n1>
<n2>20</n2>
</Add>
HTTP request: Service1.asmx
Service Oriented Architecture
Allows a collection of services to communicate with each other and
unifies processes by collecting smaller service modules in an ad hoc
manner.
Operational
Implementation
Architectural
Business
Principles
SOA Concept
SOA enables a standards-based marketplace of service
consumers and service providers across an enterprise
community or across the Web
SOA is a specification-based architecture to transition the
technical landscape to a standards-based, vendor
independent, and loosely-coupled information sharing
environment
Decoupling the service contract from the service
implementation
Promoting design and invocation by contract
Basic Components of SOA
Basic Component of SOA
De-mystifying SOA
SOA is… SOA is NOT…
A design philosophy A technology or a
and Architecture methodology
A means Not an end
A solution Not a product
Achieved through Web Only Web Services
Services and related
technologies
SOA Requirements
• Agility
• Use of standards
• Separation of concerns
• Reuse
• Interoperability between different systems and programming
languages.
• Clear and unambiguous description language
• Retrieval of the service
• Security
The Architecture
SOA - an evolution in objectives
From To
Function oriented Process oriented
Build to last Build to change
Prolonged development cycles Incrementally built and deployed
Application silos Orchestrated solutions
Tightly coupled Loosely coupled
Structuring applications using Structure applications using services
components or objects
Known implementation Implementation abstraction
The Architecture
Building an SOA - a Closer look at services
Services in a Service-Oriented Architecture are always:
Stateless:
SOA services neither remember the last thing they
were asked to do, nor care what the next is.
Discoverable:
A service must be “discoverable” by potential consumers
of the service
Self-describing:
The SOA service interface describes, exposes, and
provides an “entry point” to the service.
Composable:
SOA services are, by nature, composite.
The Architecture
Building an SOA - a Closer look at services
Single-instance
Only one implementation of a given service should exist
in an SOA.
Loosely coupled
Loose coupling allows the concerns of application features
to be separated into independent pieces.
Governed by policy
Services are built by contract.
Independent of location, language, and protocol
Services are designed to be location-transparent and
protocol/platform-independent
The Architecture
Building an SOA - a Closer look at services
As Coarse-grained as possible
Services are typically coarse-grained business functions.
Granularity is a statement of functional richness for a service –
the more coarse-grained a service is, the richer the function
offered by the service.
Potentially Asynchronous
Asynchronous communication is not required of an SOA service,
but it increases system scalability through asynchronous behavior
and queuing techniques.
SOA Infrastructure Standards
• WSS • WS-RM
• SAML • WS-RM policy
• XACML • WS-Policy
• XML-Signature • WS-Addressing
• XML-Encryption • WS-Notification
• WS-Trust
• WS-Policy • UDDI
• WS-SecurityPolicy • ebXML
• XKMS • WS-Discovery
Security Messaging Service Discovery
Mediation Governance Management
• WSDM
• XSL • WS-Management
• BPEL
• WS-Policy
• XQuery
• XPath
Steps to Implement SOA
1. Create/Expose Services
2. Register Services
3. Secure Services
4. Manage (monitor) Services
5. Mediate and Virtualize Services
6. Govern the SOA
Source: SOA Software, Inc., 2008.
1. Create & Expose Services
Three primary choices
Rebuild existing applications using SOA paradigm
Expose existing application logic as a set of services
A combination of rebuild and expose
Enterprises typically use a combination of rebuild & expose
Granularity is a key criterion for Web Service
2. Register Services
Application architects & developers need to know that a service exists
Use a registry
Source: SOA Software, Inc., 2008.
3. Secure Services
May have inadvertently created gaping security holes
May have exposed sensitive information
principles of security
4. Manage Services
Look for potential disaster
Need to be able to monitor for
Basic Availability
Performance
Throughput
SLA agreement
Source: SOA Software, Inc., 2008.
5. Mediate & Virtualize Services
As SOA matures may need to:
Introduce new versions
Increase capacity by running multiple instances
Provision applications to use specific instances of services
Solution is Virtualization
XML transformation can be used to allow consumers to use an old version of service
that no longer exists.
Consumers can provide different policy requirements for different classes of users
Transport bridging can be provided
E.g. HTTP and JMS
Meditation between different standards implementation or versions of standards
Mediation between different messaging styles
RSS, SOAP, REST, Plain old XML (POX)
Content-or-context-based routing to deliver advanced load-balancing and high-
availability capabilities
Source: SOA Software, Inc., 2008.
6. Govern the SOA
Use a governance framework
Design Time Issues
Run Time Issues
Tools needed for active participants
Service Developer needs tools to:
Publish, categorize, define meta-data, virtualize
Choose policy, participate in capacity planning & access workflow
Service Consumer needs tools to:
Facilitate service discovery, selection & access workflow
Operations Staff need to:
Monitor service performance
Troubleshoot problems, monitor dependencies
Version services, virtualization & proxy management
Source: SOA Software, Inc., 2008.
Govern the SOA Cont’d
Security Staff needs tools to:
Manage policy, report policy, check compliance, audit security
Enterprise Architect needs tools to:
Monitor application, manage relationships
Define & validate design policy
Assign services to proxy
Virtualize services
Enterprise IT Management
Manage reuse metrics
Gather service reuse statistics
Gather SOA statistics
Source: SOA Software, Inc., 2008.
Enterprise Service Bus (ESB)
ESB is the backbone of SOA that acts as a message
broker providing a message queuing system using
industry standard specifications for messaging such as
SOAP, or JMS (Java Message Service).
Expert Sally Hudson, an IDC analyst, describes the
Enterprise Service Bus as an open standards-based
messaging means designed to provide interoperability
between larger-grained applications and other
components via simple standard adapters and
interfaces.
ESB Architecture
ERP .NET Web Services
Transformation SOAP/ SOAP/ Connection Layer
(XSLT) JCA HTTP HTTP
Communication Layer
Reliable Asynchronous Secure Messaging
SOAP/ Connection Layer
HTTP JMS
C/C++ Legacy J2EE
Application
According to the SOA
A Web service is:
An interface that describes a collection of network accessible
operations
Described using a service description language
Published by making this service description available to
users
Found by sending queries to a registry matching service
descriptions
Bound-Invoked by using the information contained in the
service description
Composed with other services to create new services (service
orchestration)
How it all works together
SOA vs CORBA & DCOM
Benefits
Provides location independence: Services need not be
associated with a particular system on a particular
network
Protocol-independent communication framework
renders code reusability
Offers better adaptability and faster response rate to
changing business requirements
Allows easier application development, run-time
deployment and better service management
Benefits (cont.)
Loosely coupled system architecture allows easy
integration by composition of applications,
processes, or more complex services from other
less complex services
Provides authentication and authorization of
Service consumers, and all security functionality
via Services interfaces rather than tightly-coupled
mechanisms
Allows service consumers (ex. Web Services) to
find and connect to available Services dynamically
Thank You
Questions???
