Web Service - Distributed Software Develop - Lecture Slides | CS 682, Study notes of Software Engineering

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Distributed Software Development

Web Services^ Chris BrooksDepartment of Computer ScienceUniversity of San Francisco

Department of Computer Science — University of San Francisco – p. 1/

Service-Oriented Computing • Services are the hot new model for providing access to data orfunctionality in a distributed system. • Like objects, the definition of what a service is depends on whoyou ask. • Microsoft: A piece of business logic available via the Internetusing open standards. • DestiCorp: Encapsulated, loosely coupled contracted softwarefunctions offered via standard protocols over the Web. • Gartner: Loosely coupled software coponents that interact withone another dynamically via standard Internet technologies. • W3C: A software application identified by a URI, whoseinterfaces and binding are capable of being defined, described,and discovered by XML artifacts and supports directinteractions with other software applications using XML-basedmessages via Internet-based technologies.

Department of Computer Science — University of San Francisco – p. 2/

Services • We can think of a service as (yet another) computing metaphor. • modular functionality • Can be composed, extended and combined to provide morecomplex or extensive services.^ ◦^ This ability to compose and repurpose web services isextremely important.^ ◦^ Example: Google Maps. • Defined in terms of an interface

Department of Computer Science — University of San Francisco – p. 4/

A step back: building on the Web • Currently, the Web consists primarily of client-serverinteractions. • Web pages are the predominant objects exchanged. • No central authority. • Heterogenous, autonomous components.

Department of Computer Science — University of San Francisco – p. 5/

Next steps: Integrating Processes • Currently, most web-based interactions are stateless. • Client makes a request and returns a response. • Processes

may require long-lived multi-part interactions. ◦^ Construction of supply chains, complex orders • Services can be composed into processes. • Currently, this is done manually.

Department of Computer Science — University of San Francisco – p. 7/

Next steps: The Pragmatic Web • These combine to yield what Singh and Huhns call

the

pragmatic web

-^ Information is annotated according to its meaning and its placein a larger process. •^ In other words, information can have annotations that describe^ meaning

and^

context

-^ This provides the basis for automated negotiation. •^ This is only one possible way in which the Web may evolve, butut is one that will allow for rich, complex, dynamic interactionsbetween software components.

Department of Computer Science — University of San Francisco – p. 8/

Web Services Architectural Model S i^ ervce^ P id^ rover

S i^ ervce^ B^ k^ roer^

S i^ ervce^ R t^ equeser

1 P^ bli^ h^ us.(WSDL)

2 Di^ scover^. (UDDI)

3 Bi^ d^ n.(SOAP^ HTTP),

-^ A Web service architectureconsists of three types ofparticipants:^ ◦^

Service providers ◦ Service brokers ◦ Service requesters

-^ XML is used as the basic’glue’ language.

Department of Computer Science — University of San Francisco – p. 10/

Basic components of Web Services • HTTP • SOAP • XML • XML Schema • UDDI

Department of Computer Science — University of San Francisco – p. 11/

SOAP • SOAP (Simple Object Access Protocol) is a protocol forexchanging XML messages via HTTP. • Evolved out of XML-RPC, a protocol for performing remoteprocedure calls using XML as a message-encoding language. • SOAP consists of an

envelope

that encodes the message, and

a^ body

that contains the details of the service being invoked.

-^ On a request, the body will contain the method being invokedand any parameters. •^ On a reply, the body will contain the result of the method’sexecution.

Department of Computer Science — University of San Francisco – p. 13/

10-14:

SOAP request example

POST^

/temp

HTTP/1. Host:

www.socweather.com Content-Type:

text/xml;

charset="utf-8"

Content-Length:

xxx

SOAPAction:

"http://www.socweather.com/temp"