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Web services architecture
Web services architecture

A 'Web service' (also Web Service) is defined by the W3C as "a software system designed to support interoperable Machine to Machine interaction over a network. Interoperability is a property referring to the ability of diverse systems and organizations to work together (inter-operate M2M refers to data communications between machines M2M is most commonly translated as Machine-to-Machine but has sometimes been translated as Man-to-Machine Machine-to-Man Machine-to-Mobile A computer network is a group of interconnected Computers. Networks may be classified according to a wide variety of characteristics " Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services. WEB is a Computer programming system created by Donald E Knuth as the first implementation of what he called " Literate programming " the The Internet is a global system of interconnected Computer networks

The W3C Web service definition encompasses many different systems, but in common usage the term refers to clients and servers that communicate using XML messages that follow the SOAP standard. A client is an application or system that accesses a remote service on another Computer system, known as a server, by way of a Network. A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine Don't change "Extensible" SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using In such systems, there is often machine-readable description of the operations offered by the service written in the Web Services Description Language (WSDL). The Web Services Description Language (WSDL pronounced 'wiz-dəl' or spelled out 'W-S-D-L' is an XML -based language that provides a model for describing Web services The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side code generation in many Java and .NET SOAP frameworks (frameworks such as Spring and Apache CXF being notable exceptions). In Computer networking the term client-side refers to operations that are performed by the client in a Client-server relationship The Spring Framework (or Spring for short is an Open source Application framework for the Java platform. Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition of a Web service. The Web Services Interoperability Organization (WS-I is an industry consortium chartered to promote interoperability amongst the stack of Web services specifications

More recently, RESTful Web services have been regaining popularity. These also meet the W3C definition, and are often better integrated with HTTP than SOAP-based services. Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. They do not require XML messages or WSDL service-API definitions. The Web Services Description Language (WSDL pronounced 'wiz-dəl' or spelled out 'W-S-D-L' is an XML -based language that provides a model for describing Web services

Contents

Specifications

Profiles

To improve interoperability of Web Services, the WS-I publishes profiles. The Web Services Interoperability Organization (WS-I is an industry consortium chartered to promote interoperability amongst the stack of Web services specifications A profile is a set of core specifications (SOAP, WSDL, . SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using The Web Services Description Language (WSDL pronounced 'wiz-dəl' or spelled out 'W-S-D-L' is an XML -based language that provides a model for describing Web services . . ) in a specific version (SOAP 1. 1, UDDI 2, . . . ) with some additional requirements to restrict the use of the core specifications. The WS-I also publishes use cases and test tools to help deploying profile compliant Web Service.

Additional specifications, WS

Some specifications have been developed or are currently being developed to extend Web Services capabilities. These specifications are generally referred to as WS-*. There are a variety of specifications associated with Web services These specifications are in varying degrees of maturity and are maintained or supported by various standards bodies Here is a non-exhaustive list of these WS-* specifications.

WS-Security
Defines how to use XML Encryption and XML Signature in SOAP to secure message exchanges, as an alternative or extension to using HTTPS to secure the channel. WS-Security ( Web Services Security) is a Communications protocol providing a means for applying security to Web services On April 19 2004 the WS-Security XML Encryption, also known as XML-Enc is a specification governed by a W3C recommendation that defines how to encrypt the contents of an XML element XML Signature (also called XMLDsig, XML-DSig, XML-Sig) is a W3C recommendation that defines an XML syntax for Digital signatures SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using
WS-Reliability
An OASIS standard protocol for reliable messaging between two Web services. WS-Reliability is a SOAP -based ( 11 and 12 Part 1 OASIS specification that fulfillsreliable messaging requirements critical to some applications of Web Services The Organization for the Advancement of Structured Information Standards ( OASIS) is a Global consortium that drives the development convergence and adoption
WS-ReliableMessaging 
A protocol for reliable messaging between two Web services, issued by Microsoft, BEA and IBM it is currently being standardized by the OASIS organization [1]. WS-ReliableMessaging describes a protocol that allows SOAP messages to be delivered reliably between distributed applications in the presence of software component system or network failures Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology
WS-Addressing
A way of describing the address of the recipient (and sender) of a message, inside the SOAP message itself. WS-Addressing or Web Services Addressing is a specification of transport-neutral mechanisms that allow Web services to communicate addressing information
WS-Transaction
A way of handling transactions. A Web Services specification developed by BEA Systems, IBM, and Microsoft.

Some of these additional specifications have come from the W3C. There is much discussion around the organization's participation, as the general Web and the Semantic Web story appear to be at odds with much of the Web Services vision. The Semantic Web is an evolving extension of the World Wide Web in which the Semantics of information and services on the web is defined making it possible for the This has surfaced most recently in February 2007, at the Web of Services for the Enterprise workshop. Some of the participants advocated a withdrawal of the W3C from further WS-* related work, and a focus on the core Web.

In contrast, OASIS has standardized many Web service extensions, including Web Services Resource Framework and WSDM. The Organization for the Advancement of Structured Information Standards ( OASIS) is a Global consortium that drives the development convergence and adoption Web Services Resource Framework (WSRF is a family of OASIS -published specifications for Web services Major contributors include the Globus Alliance and

Styles of use

Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPC, SOA and REST.

Remote procedure calls

Architectural elements involved in the XML-RPC.
Architectural elements involved in the XML-RPC.

RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Remote procedure call ( RPC) is an Inter-process communication technology that allows a Computer program to cause a Subroutine or procedure to Typically, the basic unit of RPC Web services is the WSDL operation.

The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticised for not being loosely coupled, because it was often implemented by mapping services directly to language-specific functions or method calls. Loose coupling describes a resilient relationship between two or more systems or organizations with some kind of exchange relationship Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile. The WS-I Basic Profile (official abbreviation is BP a specification from the Web Services Interoperability industry consortium (WS-I provides Interoperability

Service-oriented architecture

Web services can also be used to implement an architecture according to Service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. Service-oriented architecture ( SOA) is a method for Systems development and integration where functionality is grouped around Business processes This is often referred to as "message-oriented" services.

SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details. Loose coupling describes a resilient relationship between two or more systems or organizations with some kind of exchange relationship

Representational state transfer

Finally, RESTful Web services attempt to emulate HTTP and similar protocols by constraining the interface to a set of well-known, standard operations (e. g. , GET, PUT, DELETE). Here, the focus is on interacting with stateful resources, rather than messages or operations. RESTful Web services can use WSDL to describe SOAP messaging over HTTP, which defines the operations, or can be implemented as an abstraction purely on top of SOAP (e. g. , WS-Transfer).

WSDL version 2.0 offers support for binding to all the HTTP request methods (not only GET and POST as in version 1. The Web Services Description Language (WSDL pronounced 'wiz-dəl' or spelled out 'W-S-D-L' is an XML -based language that provides a model for describing Web services Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. 1) so it enables a better implementation of RESTful Web services[1]. However support for this specification is still poor in software development kits, which often offer tools only for WSDL 1. A software development kit ( SDK or " devkit " is typically a set of development tools that allows a Software engineer to create applications 1.

Criticisms

Critics of non-RESTful Web services often complain that they are too complex[2] and biased towards large software vendors or integrators, rather than open source implementations. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge

One big concern of the REST Web Service developers is that the SOAP WS toolkits make it easy to define new interfaces for remote interaction, often relying on introspection to extract the WSDL and service API from Java, C# or VB code. In Computing, type introspection is a capability of some Object-oriented programming languages to determine the type of an object at Runtime This is viewed as a feature by the SOAP stack authors (and many users) but it is feared that it can increase the brittleness of the systems, since a minor change on the server (even an upgrade of the SOAP stack) can result in different WSDL and a different service interface. The client-side classes that can be generated from WSDL and XSD descriptions of the service are often similarly tied to a particular version of the SOAP endpoint and can break if the endpoint changes or the client-side SOAP stack is upgraded. Well designed SOAP endpoints (with handwritten XSD and WSDL) do not suffer from this but there is still the problem that a custom interface for every service requires a custom client for every service. XML Schema, published as a W3C recommendation in May 2001 is one of several XML schema languages.

There are also concerns about performance due to Web services' use of XML as a message format and SOAP and HTTP in enveloping and transport.

Similar efforts

There are several other approaches to solving the set of problems that Web services address, both preceding and contemporary to it. RMI was one of many middleware systems that have seen wide deployment. The Java Remote Method Invocation API, or Java RMI, is a Java application programming interface for performing the object equivalent of Remote procedure Middleware is computer Software that connects Software components or applications More ambitious efforts like CORBA and DCOM attempted to effect distributed objects, which Web services implementations sometimes try to mimic. The Common Object Requesting Broker Architecture (CORBA is a standard defined by the Object Management Group (OMG that enables software components written Distributed Component Object Model ( DCOM) is a proprietary Microsoft technology for communication among software components distributed across Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs

More basic efforts include XML-RPC, a precursor to SOAP that was only capable of RPC, and various forms of HTTP usage without SOAP. XML-RPC is a Remote procedure call protocol which uses XML to encode its calls and HTTP as a transport mechanism Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet.

See also

Notes

  1. ^ Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts. The Devices Profile for Web Services (DPWS defines a minimal set of implementation constraints to enable secure Web Service messaging discovery description and eventing on The OGC Web Processing Service ( WPS) is designed to standardize the way that GIS calculations are made available to the Internet The term web server can mean one of two things A Computer program that is responsible for accepting HTTP requests from web clients which are Microsoft Connected Services Framework (CSF is a service-aggregation SOA platform from Microsoft. Web services provide access to software systems over the Internet using standard protocols OAuth is an open protocol initiated by Blaine Cook and Chris Messina, to allow secure API Authorization in a simple and standard method for Service-oriented modeling is a Software development methodology that employs disciplines and a universal language to provide tactical and strategic solutions to enterprise
  2. ^ ongoing · WS-Pagecount

External links

Dictionary

web service

-noun

  1. (computing) a software system designed to support interoperable machine-to-machine interaction over a network
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