Transcript Web Service - Nile University

Ahmed Gamal Ahmed
Nile University
Bioinformatics Group
Agenda
 Web Service Over View
 SOAP
 WSDL
 UDDI
Web Service Over View
 What are Web services?
a standardized way of integrating Web-based
applications using the XML, SOAP, WSDL and UDDI
open standards over an Internet protocol backbone.
 XML is used to tag the data
 SOAP is used to transfer the data
 WSDL is used for describing the services available
 UDDI is used for listing what services are available.
Web Service Over View
 Why there is a need for Web services?
Web services' distributed computing model allows
application-to-application communication.
Web services allow different applications from different
sources to communicate with each other without timeconsuming custom coding, and because all communication
is in XML, Web services are not tied to any one operating
system or programming language.
Because of this level of application integration, Web
services have grown in popularity and are beginning to
improve business processes. In fact, some even call Web
services the next evolution of the Web.
Web Service Over View
 Basic Architecture
 The basic architecture includes Web services
technologies capable of:
 Exchanging messages
 Describing Web services
 Publishing and discovering Web service descriptions
Web Service Over View
 Service-Oriented Architecture
 SOA is a specific architectural style that is concerned
with loose coupling and dynamic binding between
services. Some critically important factors at the heart
of SOA are necessary to make it work effectively.
Web Service Over View
Web Service Over View
 Components
1.
The Service:
A
service is a software module deployed on
network accessible platforms provided by the
service provider.
 It exists to be invoked by or to interact with a
service requestor.
 It may also function as a requestor, using other
web services in its implementation.
Web Service Over View
 Components
2. The Service Description:

The service description contains the details of the
interface and implementation of the service.

This includes its data types, operations, binding
information, and network location.

It could also include categorization and other meta
data to facilitate discovery and utilization by
requestors.

The service description may be published to a
requestor directly or to a discovery agency.
Web Service Over View
 Roles
1.
Service Provider:
From a business perspective, this is the owner of the
service.
 From an architectural perspective, this is the platform
that hosts access to the service.
 It has also been referred to as a service execution
environment or a service container.
 Its role in the client-server message exchange patterns
is that of a server.

Web Service Over View
 Roles
2. Service Requestor:
 From a business perspective, this is the business that
requires certain function to be satisfied.
 From an architectural perspective, this is the
application that is looking for and invoking or
initiating an interaction with a service.
 The requestor role can be played by a browser driven
by a person or a program without a user interface,
e.g. another web service.
 Its role in the client-server message exchange patters
is that of a client.
Web Service Over View
 Roles
2. Discovery Agency:
 This is a searchable set of service descriptions where
service providers publish their service descriptions.
 The service discovery agency can be centralized or
distributed.
 A discovery agency can support both the pattern where it
has descriptions sent to it and where the agency actively
inspects public providers for descriptions.
 Service requestors may find services and obtain binding
information (in the service descriptions) during
development for static binding, or during execution for
dynamic binding.
Web Service Over View
 Operations
Publish:
 In order to be accessible, a service needs to publish
its description such that the requestor can
subsequently find it.
 Where it is published can vary depending upon the
requirements of the application.
1.
Web Service Over View
 Operations
2. Find:
 The service requestor retrieves a service description
directly or queries the registry for the type of service
required .
 The find operation may be involved in two different
lifecycle phases for the service requestor:
i. At design time in order to retrieve the service's
interface description for program development
ii. At runtime in order to retrieve the service's binding
and location description for invocation.
Web Service Over View
 Operations
 Interact: Eventually, a service needs to be invoked. In
the interact operation the service requestor invokes or
initiates an interaction with the service at runtime
using the binding details in the service description to
locate, contact, and invoke the service. Examples of
the interaction include: single message one way,
broadcast from requester to many services, a multi
message conversation, or a business process. Any of
these types of interactions can be synchronous or
asynchronous.
Web Service Over View
XML—The Backbone of Web Services
XML—The Backbone of Web Services
XML—The Backbone of Web Services
 The XML markup, in much the same way as HTML, is
in the form of tags(e.g., <tag>, <name>, <price>,
<wife>, and so forth).
XML—The Backbone of Web Services
 XML namespaces
 Name Conflicts
 In XML, element names are defined by the developer.
This often results in a conflict when trying to mix XML
documents from different XML applications.
XML—The Backbone of Web Services
 This XML carries HTML table information:
 This XML carries information about a table (a piece of
furniture):
XML—The Backbone of Web Services
 Solving the Name Conflict Using a Prefix
Name conflicts in XML can easily be avoided using a
name prefix.
XML—The Backbone of Web Services
 XML Namespaces - The xmlns Attribute
 When using prefixes in XML, a so-called namespace
for the prefix must be defined.
 The namespace is defined by the xmlns attribute in
the start tag of an element.
 The namespace declaration has the following syntax.
xmlns:prefix="URI".
XML—The Backbone of Web Services
The namespace URI is NOT used by the parser to look up
information.
Web Service Stack
Basic Web Service Usage Scenario
Web Services Implementation
 Application Server (web service-enabled)






– provides implementation of services and exposes it through WSDL/SOAP
– implementation in Java, as EJB, as .NET (C#) etc.
SOAP server
– implements the SOAP protocol
HTTP server
– standard Web server
SOAP client
– implements the SOAP protocol on the client site
SOAP – Simple Object Access Protocol
 SOAP consists of
– Envelope construct: defines the overall structure of messages
– Encoding rules: define the serialization of application data types
– SOAP RPC: defines representation of remote procedure calls
and responses
– Binding framework: binding to protocols such as HTTP, SMTP
– Fault handling
 Soap supports advanced message processing:
–
forwarding intermediaries: route messages based on the semantics of
message
– active intermediaries: do additional processing before forwarding
messages, may modify message
SOAP – Simple Object Access Protocol
SOAP Messages
 SOAP messages consist of
– Envelope: top element of XML message (required)
– Header: general information on message such as security (optional)
– Body: data exchanged (required)
 Header
– elements are application-specific
– may be processed and changed by
intermediaries or recipient
 Body
– elements are application-specific
– processed by recipient only
SOAP – Simple Object Access Protocol
Example: SOAP Message
SOAP – Simple Object Access Protocol
Protocol Binding
 Bindings to different protocols possible: HTTP, SMTP
 Different HTTP bindings: HTTP POST, HTTP GET
– standard HTPP POST for request-response
WSDL – Web Service Description Language
 Description of Web services in XML format
– abstract description of operations and their parameters (messages)
– binding to a concrete network protocol (e.g. SOAP)
– specification of endpoints for accessing the service
 Structure of a WSDL document
WSDL – Web Service Description Language
Overview of Defining WSDL Services
1.
2.
Define in XML Schema the message types used when invoking the
service: MT1, MT2 etc.
Define (named) messages by using these types, e.g.


3.
Define Services that consist of one or more operations; each
operation is implemented by the exchange of messages

4.
service S offers operation O1; for executing O1 first send a request
message m1, then a response message m2 is returned
Define a Binding B to a specific protocol, e.g. SOAP

5.
message m1 has type MT1
message m2 has type MT2 etc.
service S is implemented in SOAP; the SOAP messages are
constructed from the abstract messages m1 and m2 by, e.g. inlining
the message as body of SOAP messages
Service S is provided with binding B at the following URI's (called
ports)
WSDL – Web Service Description Language
Example: Overall Document Structure
WSDL – Web Service Description Language
Example: Definition of Types
WSDL – Web Service Description Language
Example: Definition of Messages and PortType
WSDL – Web Service Description Language
Example: Definition of Binding and Service
WSDL – Web Service Description Language
PortTypes
 WSDL supports 4 message patterns that an endpoint (=service provider!) can
support for an operation



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one-way: message is sent to service provider without expecting response
request-response: request is sent to service provider expecting response
solicit-response: provider sends a message and expects response
notification: message is sent by service provider
 Message patterns are distinguished by the use of input/output elements
 one way:
 request/response:
UDDI – Universal Description Discovery and
Integration
 Universal Description and Discovery and Integration
 UDDI consists of
 A specification for how to build a registry of business,
services and how to connect to them
 A standards committee that is working on revising and
improving the specification
 Agreement to operate solutions that conform to the
specification
UDDI – Universal Description Discovery and
Integration
 UDDI Business Registry consist of
 White pages – general information regarding business
 Yellow pages – arranged by geography or industry code
 Green pages – list protocols supported by each business
 Information stored in XML format