Distributed Systems. Web Services (WS) and Service Oriented Architectures (SOA) László Böszörményi Distributed Systems Web Services - 1

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1 Distributed Systems Web Services (WS) and Service Oriented Architectures (SOA) László Böszörményi Distributed Systems Web Services - 1

Service Oriented Architectures (SOA) A SOA defines, how services are offered and used Services can be orchestrated to a business process This can be offered as a service again Some characteristics

2 Service Oriented Architectures (SOA) A SOA defines, how services are offered and used Services can be orchestrated to a business process This can be offered as a service again Some characteristics Distributed, heterogeneous, loosely coupled, dyn. bound Web Services WSDL, UDDI, SOAP RESTful services Directly over HTTP Stateless (as HTTP), point-to-point ESB (Enterprise Service Bus) László Böszörményi Distributed Systems Web Services - 2

3 Web Services Definition and Goals Provide services relying on XML descriptions Enabling the programmable Web (client/server m.) Most universal communication vehicle is still: text More exactly: semi-structured text: XML Basic goals of Web Services ( Web Servers!) Loosely coupled services in any combination E.g. a travel agent service, relying on flight and hotel services Grids and clouds may also be based on Web Services Interconnection over internet or intranet Distribution and integration of application logic Component-like, reusable black boxes László Böszörményi Distributed Systems Web Services - 3

4 Combined Web Services Example The Travel Agent Web Service relies on the Web Services of flight, hotel and car booking Enabling Technology flight booking a flight booking b Client Travel Agent Service hire car booking a hotel booking a hotel booking b hire car booking b László Böszörményi Distributed Systems Web Services - 4

5 Web Services Basic Technology WSDL WHAT Web Services Description Language UDDI WHERE Universal Description, Discovery and Integration UDDI Registry 2 WSDL Document SOAP HOW Simple Object Access Protocol Client queries registry to locate service 2. Registry refers to WSDL document 3. Client accesses WSDL 4. WSDL provides data for interaction with WS 5. Clients sends request to WS via SOAP 6. Web Service replies via SOAP Client 5 6 Web Service László Böszörményi Distributed Systems Web Services - 5

6 Web Services Architecture Some services on the application level are generally available (e.g. directory, security) Applications Directory service Security Choreography Web Services Service descriptions (in WSDL) SOAP URIs (URLs or URNs) XML HTTP, SMTP or other transport László Böszörményi Distributed Systems Web Services - 6

7 Web Services Some Characteristics Supported by many platforms Java, the.net Framework, JAXP, ASP.NET WS Based on open standards HTTP, XML and SOAP Overcome some shortages of available solutions ASPs (Application Service Providers) provide typically coarse grained services WS also fine grained CORBA, DCOM scale wrong, because of tight coupling DCOM is limited to Windows EJB (Enterprise Java Beans) is restricted to Java Component based architecture required László Böszörményi Distributed Systems Web Services - 7

8 Web Services Infrastructure Request.vsdisco Discovery Return disco (XML) Web Service Client Request WSDL Description Return WSDL (XML) Request.asmx Protocol Return response (XML) Web Service László Böszörményi Distributed Systems Web Services - 8

9 SOAP - Basics Designed both for messaging and RPC Structural elements described by XML Schemes Specifies three parts SOAP envelope for message framework SOAP encoding for standard, interoperable marshaling SOAP RPC as RPC-convention on the top of HTTP SMTP, TCP, UDP as basis are also possible SOAP message structure Envelope Header for handling instructions Body for XML Payload László Böszörményi Distributed Systems Web Services - 9

10 SOAP Message Structure envelope header header element header element body body element body element László Böszörményi Distributed Systems Web Services - 10

11 Selected Amazon Web Services László Böszörményi Distributed Systems Web Services - 11

XML Web Service? A programmable component Provides a particular function for an application Can be published, located, and invoked across the Web

Web Services. XML Web Service? A programmable component Provides a particular function for an application Can be published, located, and invoked across the Web Platform: Windows COM Component Previously