Web Services explained for dummies

1. Introduction to WebServices
-Gagandeep Singh

2. What are Web Services
Web services are client and server applications that communicate over the
World Wide Web’s (WWW) Hypertext Transfer Protocol (HTTP).
As described by the World Wide Web Consortium (W3C), web services
provide a standard means of interoperating between software applications
running on a variety of platforms and frameworks. Web services are
characterized by their great interoperability and extensibility, as well as their
machine-processable descriptions, thanks to the use of XML.
Web services can be combined in a loosely coupled way to achieve complex
operations. Programs providing simple services can interact with each other
to deliver sophisticated added-value services.

3. Service Oriented Architecture (SOA)
A service-oriented architecture is essentially a collection of services. These
services communicate with each other. The communication can involve either
simple data passing or it could involve two or more services coordinating
some activity.
Some means of connecting services to each other is needed.
Service-oriented architectures are not a new thing. The first service-oriented
architecture for many people in the past was with the use DCOM or Object
Request Brokers (ORBs) based on the CORBA specification.

4. Service
If a service-oriented architecture is to be effective, we need a clear
understanding of the term service. A service is a function that is well-
defined, self-contained, and does not depend on the context or state of
other services
Services are what you connect together using Web Services. A service is the
endpoint of a connection. Also, a service has some type of underlying
computer system that supports the connection offered. This section
provides information on the specification of services.
“a service is a type of API, usually over HTTP”
You may have an API, but not expose it to anybody external.
“a service is a proxy of your internal logic, which is exposed to the outside
world”
Think of the analogy of “views” in database systems.

5. Connections
The technology of Web Services is the most likely connection technology of
service-oriented architectures. The following figure illustrates a basic service-
oriented architecture. It shows a service consumer at the right sending a service
request message to a service provider at the left. The service provider returns a
response message to the service consumer. The request and subsequent response
connections are defined in some way that is understandable to both the service
consumer and service provider.

6. Introduction to Service Oriented Computing
-Context of WebServices: Distributed Information Systems
Layers of an information system
Presentation layer
Communication interface to external entities
Graphical user interface for human users or non
graphical user interface for other programs
Application logic layer
Implements operations requested by clients
through the presentation layer
Resource management layer
Deals with different data sources of an
information system
Distributed systems are split up into parts
Run simultaneously on multiple computers
Communicate over a network
Client
Resource Management
Layer
Application Logic Layer
Presentation layer

7. Machine to machine communication
-Getting applications to talk to each other
Client
Resource Management
Layer
Application Logic Layer
Presentation layer
Client
Resource Management
Layer
Application Logic Layer
Presentation layer
Application Logic Layer

8. Example: Yield management in the airline industry requires close system
interaction in order to retrieve the most current prices
Windows Server 2008 UNIX System
Travel Information and
Booking Application
(programmed in Java)
Flight Information and
Booking Application
(programmed in C)
Seamless
Interaction
Mismatch in operating system, language, platform, etc.
Service-oriented computing is an emergent paradigm that helps to
overcome these mismatches

9. Windows Server 2008 UNIX System
Travel Information and
Booking Application
(programmed in Java)
Flight Information and
Booking Application
(programmed in C)
Request
Response

10. Service Vs WebService
Services are business functions which an enterprise offers to its business
Partners
A possible implementation of Services are Web Services
 However, other concepts may also be used to implement a Service, e.g.,
ebXML, document-centric approaches using EDI messages, etc.

11. Important terms in SOA
(Web) Services are self-contained modules that can be described, published,
located, orchestrated, and programmed using XML-based technologies over a
Network.
Service providers are organizations that provide the service implementations,
supply their service descriptions, and provide related technical and business
Support.
Service clients are end-users and organizations that use some service.
Service aggregators are organizations that consolidate multiple services into a
new, single orchestrated service offering that is commonly known as business
process.
A service-oriented architecture (SOA) is a logical way of designing a software
system to provide services to either end-user applications or to other services
distributed in a network, via published and discoverable interfaces.

12. Types of Web Services
On the conceptual level, a service is a software component provided through a
network-accessible endpoint. The service consumer and provider use messages
to exchange invocation request and response information in the form of self-
containing documents that make very few assumptions about the technological
capabilities of the receiver.
On a technical level, web services can be implemented in various ways. The two
types of web services discussed in this section can be distinguished as “big” web
services (SOAP) and “RESTful” web services.

13. SOAP provides the envelope for sending Web Services messages over the
Internet/Internet. It is part of the set of standards specified by the W3C. SOAP is an
alternative to Representational State Transfer (REST) and JavaScript Object Notation
(JSON).
The SOAP envelope contains two parts:
An optional header providing information on
authentication, encoding of data, or how a recipient
of a SOAP message should process the message.
The body that contains the message. These
messages can be defined using the WSDL
specification.
SOAP commonly uses HTTP, but other protocols such
as Simple Mail Transfer Protocol (SMTP) may by used.
SOAP can be used to exchange complete documents
or to call a remote procedure.
NOTE: SOAP at one time stood for Simple Object
Access Protocol. Starting with SOAP Version 1.2, the
letters in the acronym have no particular meaning.
Simple Object Access Protocol(SOAP)

14. SOAP
SOAP was originally part of the specification that included the Web Services
Description Language (WSDL) and Universal Description, Discovery, and
Integration (UDDI). It is used now without WSDL and UDDI. Instead of the
discovery process, SOAP messages are hard-coded or generated without the
use of a repository. The interaction is illustrated in the figure below.

15. “Big” Web Services(SOAP Based)
Big web services use XML messages that follow the Simple Object Access Protocol (SOAP)
standard, an XML language defining a message architecture and message formats. Such
systems often contain a machine-readable description of the operations offered by the
service, written in the Web Services Description Language (WSDL), an XML language for
defining interfaces syntactically.
The SOAP message format and the WSDL interface definition language have gained
widespread adoption. Many development tools, such as NetBeans IDE, can reduce the
complexity of developing web service applications.

16. Representational State Transfer (REST)
Representational State Transfer (REST) is a style of architecture based on a set of
principles that describe how networked resources are defined and addressed. These
principles were first described in 2000 by Roy Fielding as part of his doctoral
dissertation.
REST is an alternative to SOAP and JavaScript Object Notation (JSON).
It is important to note that REST is a style of software architecture as opposed to a set
of standards. As a result, such applications or architectures are sometimes referred to
as RESTful or REST-style applications or architectures. REST has proved to be a
popular choice for implementing Web Services. It is one of the options for Amazon
Web Services
An application or architecture considered RESTful or REST-style is characterized by:
State and functionality are divided into distributed resources.
Every resource is uniquely addressable using a uniform and minimal set of
commands (typically using HTTP commands of GET, POST, PUT, or DELETE over the
Internet)
The protocol is client/server, stateless, layered, and supports caching
This is essentially the architecture of the Internet and helps to explain the popularity
and ease-of-use for REST

17. REST
Representation State Transfer (REST) appeals to developers because it has a
simpler style that makes it easier to use than SOAP. It also less verbose so that
less volume is sent when communicating.

18. RESTful Web Services
In Java EE 6, JAX-RS provides the functionality for Representational State
Transfer (RESTful) web services. REST is well suited for basic, ad hoc integration
scenarios. RESTful web services, often better integrated with HTTP than SOAP-
based services are, do not require XML messages or WSDL service–API
definitions.
Project Jersey is the production-ready reference implementation for the JAX-RS
specification. Jersey implements support for the annotations defined in the JAX-
RS specification, making it easy for developers to build RESTful web services
with Java and the Java Virtual Machine (JVM).
Because RESTful web services use existing well-known W3C and Internet
Engineering Task Force (IETF) standards (HTTP, XML, URI, MIME) and have a
lightweight infrastructure that allows services to be built with minimal tooling,
developing RESTful web services is inexpensive and thus has a very low barrier
for adoption. You can use a development tool such as NetBeans IDE to further
reduce the complexity of developing RESTful web services.

19. JavaScript Object Notation (JSON)
JavaScript Object Notation (JSON) uses name/value pairs. This is similar to the
tags used by XML. An example from the figure below shows, at the left, the XML
tag of "<state>" with the value of "MN." The pairs for JSON are at the right. It
similarly shows the name "state" is paired with the value "MN." The name/value
pairs do not need to be in a specific order. Also, like XML, JSON provides
resilience to changes and avoids the brittleness of fixed record formats.

20. While both SOAP and REST use XML for interchange, JavaScript Object Notation
(JSON) uses a subset of JavaScript. This is illustrated in the figure below.

21. Characteristics of Web Services
WS semantically encapsulate discrete functionality
A Web Service is a self contained software module that performs a single task
(e.g. weather forecast by passing the zip-code as parameter)
WS share a contract
In order to allow interaction of services, a formal contract must be established,
that defines the exact terms of an information exchange between a service client
and a service provider
WS abstract underlying program logic
A service exposes a certain functionality to a client. How that functionality is
achieved (e.g., which program language is used, or which database is used)
remains invisible to the caller)
WS are loosely coupled software modules
A service interface is defined in a neutral manner, independent of the
underlying platform, operating system, or programming language
Due to their neutral interfaces, services are not hard-wired. Thus, a service may
be easily exchanged by another service, without much implementation effort

22. WS are reusable
A service may be reused by multiple applications
WS can be dynamically found and included in applications
A WS provides programmable access. Thus, a WS may be embedded in a
remotely located application, i.e., a service may be composed.
Unlike Web Sites, Web Services are not targeted at human users
They are called by and exchange data with other software modules and
applications.
WS are described in terms of a standard description language
Web Service Description Language (WSDL) and Web Application Description
Language (WADL) describe functional service characteristics
Functional requirements: Requirements of the functionality which must be
provided (Functions, Data, Behaviour, etc.)
Non-functional requirements: Requirements of the circumstances under which the
functionality must be provided (e.g., reliability, performance, etc.)
WS are distributed over the Internet
 WS make use of existing ubiquitous transport Internet protocols like HTTP
By relying on the same well-understood transport mechanism as Web Content,
Web Services may leverage existing infrastructures and may cross corporate
firewalls.

23. Operations in a Web Service
Architecture
Publish
A service description needs to be published such that
the service requestor can find it
it is accessible
Find
The service requestor retrieves the service description
directly
by querying a service registry
Bind
The service requestor invokes or instantiates the interaction with the
service by using binding details in the service description to locate,
contact,
and invoke the service.

24. Standards in use
Service
Service
Provider
Service
Requestor
WSDL WSDL
SOAP
UDDI
Find
Bind
Publish
Note, that finding and publishing a service is also realized using SOAP calls