Web Services
Definisi
• Menurut W3C [6] Web service adalah suatu
sistem perangkat lunak yang didisain untuk
mendukung interaksi mesin ke mesin pada suatu
jaringan.
• menurut Michael C. Daconta, Web Service
adalah aplikasi perangkat lunak yang dapat
ditemukan, diuraikan, dan diakses berdasarkan
pada XML dan protokol standard Web pada
intranet, extranet, dan Internet.
What Is Web Services
Example: Web based purchase
Credit
Service
Purchase
Invoice
Order
Consolidate
Results
PO Service
Web services are self contained, self describing, modular applications
that can be published, located, and invoked across the web. Web
services perform functions, which can be anything from simple requests
to complicated business processes".
---- According to IBM
Figure Taken from Oracle Session id: 40024
Service
Integration
Directory
Service
Search / Use
Service
Description
Features Of Web Services
Service
Description
Virtual Travel
Agency
Migration Of Existing web Application
Service
Description
Standards are the Base
Communicate using messages
Robust , Effective, Flexible Security
Services Description
Web Service Discovery
Figure Taken from Intelligent agent course 2003/2004 by Dr. Omar Belakhdar
Why to use more than one
computer?
• Distributed resources
– access to shared data
– access to shared programs
– access to CPU (e.g. many desktop PCs together), to
memory, to special devices (e.g. printer)
• Complete independence on the internal
implementation
Distributed architecture
• gives
– access to distributed resources
– development encapsulation
• maintainability, re-usability, legacy-awareness
– implementation independence
• requires
– adding a communication layer between parts
– synchronization of efforts
• including such nasty things as distributed garbage
collection
Distributed architecture
Waiting for
requests
Communication protocol, Data format
(known location,
known port)
Sending
requests,
getting
results
• Basic questions are:
– What kind of protocol to use, and what data to
transmit
– What to do with requests on the server side
Traditional CGI-based approach
Waiting for
requests
(known location,
known port)
Data as name/value pairs
Sending
requests,
getting
results
• cgi-bin scripts:
–
–
–
–
Data transmitted as name-value pairs (HTML forms)
Transport over (state-less) HTTP protocol
no standards for keeping user sessions (state-fullness)
server side: a script is called
CORBA-based approach
Waiting for
requests
(known location,
known port)
Data in binary format
Sending
requests,
getting
results
• CORBA:
–
–
–
–
Data transmitted as objects (at least it looks like that)
Transport (usually) over well standardised IIOP protocol
user sessions (state-fullness) very inter-operable
server side: an RPC call is made
SOAP-based communication
Waiting for
requests
Data in XML format
(known location,
known port)
Sending
requests,
getting
results
• SOAP:
– Data in a well-defined XML format
– Transport over various protocols
• HTTP, SMTP are the most used, perhaps because they are
firewall-friendly
– server side: either an RPC call or a message delivered
Web services
• A collection of XML-based technologies
developed by the e-business community to
address issues of:
– service discovery
– interoperable data exchange and/or application
invocation
– service compositions (workflow, business processes)
• Major developers include:
– Apache, IBM, HP, SUN & Microsoft (.NET)
• http://www.webservices.org/
W3C (working group) definition
• "A Web service is a software application identified by a
URI, whose interfaces and bindings are capable of being
defined, described and discovered as XML artefacts. A
Web service supports direct interactions with other
software agents using XML based messages exchanged
via internet-based protocols."
• http://www.w3c.org/TR/2002/WD-wsa-reqs-20020819
Characteristics of Web services
• Providing services to other computer programs
(not to Web browsers)
• Interoperability between software applications
running on different computers
• Loosely coupled
• Machine-processable
• Use of standards: XML, HTTP, SOAP, WSDL
Basic idea of Web services
• Exchange of messages
– Messages are encoded using XML
•  SOAP
• – Using standard protocols to transport messages
– HTTP, SMTP, . . .
• • Message can be sent:
• – One-way: Call the service, but don’t expect an answer
• ! asynchronous messaging
• – Request / response: Call the service and wait for the
response
• ¤ most common style
• ¤ synchronous messagging
•
•
•
•
•
SOAP (Simple Object Access Protocol)
Extensible Markup Language (XML)
Hypertext Transport Protocol (HTTP)
Web Services Description Language (WSDL)
Universal Discovery Description Integration (UDDI)
. Langkah 1, aplikasi klien menemukan informasi tentang Web Service A
dalam suatu UDDI registry. Langkah 2, aplikasi klien mendapatkan WSDL
untuk Web Service A dari UDDI registry untuk menentukan API milik
Web Service A. Akhirnya, pada langkah 3 dan 4, aplikasi klien
berkomunikasi dengan Web Service melalui SOAP, menggunakan API yang
ditemukan dalam langkah 2.
State of the Art
• UDDI provides a mechanism for clients to find web services.
• WSDL defines services as collections of network endpoints or
ports. A port is defined by associating a network address with a
binding; a collection of ports define a service.
• SOAP is a message layout specification that defines a uniform
way of passing XML-encoded data. It also defines a way to bind
to HTTP as the underlying communication protocol. SOAP is
basically a technology to allow for “RPC over the web”.
State of the Art
UDDI
WSDL
SOAP
URI
HTML
HTTP
Web Services Stack
•
•
•
•
•
SOAP (Simple Object Access Protocol)
Extensible Markup Language (XML)
Hypertext Transport Protocol (HTTP)
Web Services Description Language (WSDL)
Universal Discovery Description Integration (UDDI)
• SOAP adalah spesifikasi yang mendefinisikan tata tata
bahasa XML untuk mengirim (request) dan
menanggapi (respond) pesan yang diterima dari pihak
lain.
• Standar SOAP memiliki dua bagian :
– Header yang membawa proses instruksi
– Body yang berisi payload (berisi informasi yang dikirim)
• Pesan SOAP ada 3 tipe :
– Dokumen (XML)
– RPC (Remote Procedure Calls)
XML Messaging Using SOAP
• WSDL adalah sebuah spesifikasi yang berbasis XML
yang digunakan untuk mendeskripsikan apa yang akan
dilakukan oleh Web Service dan bagaimana untuk
mengoperasikannya
• WSDL memiliki bagian-bagian yang berisi detail
bagaimana membuat koneksi ke service disimpan
WSDL
• Web Services Definition Language
– http://www.w3.org/TR/wsdl/
• An XML-based language for describing Web
Services
– what the service does (description)
– how to use it (method signatures)
– where to find the service
• It does not depend on the underlying protocol
• But: It is not much human-readable
• UDDI adalah sebuah spesifikasi XML yang
menggambarkan bagaimana calon pelanggan
dari layanan Web bisa belajar tentang kemampuannya
dan memperoleh informasi dasar
yang dibutuhkan untuk membuat kontak awal dengan
situs
• Registry UDDI bisa public, private, atau semiprivate
UDDI (and alternatives)
• Universal Description, Discovery and Integration
– http://www.uddi.org
• UDDI creates a platform-independent, open
framework & registry for:
– Describing services
– Discovering businesses
– Integrating business services
• The UDDI may be less used than predicted,
especially on the Internet level
• BioMoby - an alternative for Life Sciences domain?
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Mengintegrasikan sistem-sistem legacy
Menurunkan biaya operasional
Menurunkan biaya pengembangan software
pengembangan sistem dilakukan lebih cepat
Antarmuka yang lebih baik untuk pelanggan
Integrasi yang lebih baik dengan partner bisnis
Peluang pendapatan baru
Merupakan model bisnis baru
• Kesulitan tersembunyi dari Layanan Web :
– Masalah ketersediaan
– Matching Requirements
– Immutable Interfaces
– Guaranteed Execution
• Memiliki masalah pada performance nya
• Standarisasi Web service belum lengkap atau
belum final