Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Web Service shopping experience:
1. Compare - without doubt the biggest advantage that the Web Service offers shoppers today is the ability to compare thousands of Web Service at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Web Service? Wrong! If the Web Service is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Web Service then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Web Service? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Web Service and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Web Service wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Web Service then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Web Service site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Web Service, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Web Service, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
The
W3C defines a
Web service (many sources also capitalize the second word, as in Web
Services) as "a software system designed to support interoperability Machine to Machine interaction over a computer network." Web services are frequently just Web
application programming interfaces that can be accessed over a network, such as the
Internet, and executed on a remote system hosting the requested services.
The W3C Web service definition encompasses many different systems, but in common usage the term refers to
Client (computing) and Server (computing) that communicate using
XML messages that follow the SOAP standard. Common in both the field and the terminology is the assumption that there is also a machine readable description of the operations supported by the
server (computing) written in the
Web Services Description Language (WSDL). The latter is not a requirement of a SOAP
endpoint, but it is a prerequisite for automated
client-side code generation in the mainstream Java (programming language) and Microsoft .NET SOAP frameworks. Some industry organizations, such as the
WS-I, mandate both SOAP and WSDL in their definition of a Web service.
Specifications
Core specifications
The specifications that define
Web services are intentionally modular, and as a result there is no one document that contains them all. Additionally, there is neither a single, nor a stable set of specifications. There are a few "core" specifications that are supplemented by others as the circumstances and choice of technology dictate, including:
SOAP: An XML-based, extensible message envelope format with "bindings" to underlying protocols. The primary protocols are
HTTP and
HTTPS, although bindings for others, including
Simple Mail Transfer Protocol and Extensible Messaging and Presence Protocol, have been written.Web Services Description Language (WSDL): An
XML format that allows service interfaces to be described along with the details of their bindings to specific protocols. Typically used to generate server and client code, and for configuration.Universal Description, Discovery, and Integration (
UDDI): A protocol for publishing and discovering metadata about Web services that enables applications to find them, either at design time or runtime.
Most of these core specifications have come from World Wide Web Consortium, including XML,
SOAP, and Web Services Description Language; UDDI comes from
OASIS (organization).
See List of Web service specifications for a more complete listing.
Profiles
To improve interoperability of Web Services, the WS-I publishes profiles. A profile is a set of core specifications (SOAP, WSDL, ...) 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-*. 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-Reliability: An
OASIS (organization) standard protocol for reliable messaging between two Web services.
WS-ReliableMessaging A protocol for reliable messaging between two Web services, issued by
Microsoft, BEA Systems and IBM it is currently being standardized by the OASIS organization http[WS-Addressing: A way of describing the address of the recipient (and sender) of a message, inside the SOAP message itself.
WS-Transaction: A way of handling transactions.
Some of these additional specifications have come from the
World Wide Web Consortium. 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. 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 (organization) has standardized many Web service extensions, including
Web Services Resource Framework and
WSDM.
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
Remote procedure call Web services present a distributed function (or method) call interface that is familiar to many developers. 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 Loose coupling, because it was often implemented by mapping services directly to language-specific function or method calls... Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the
WS-I Basic Profile.
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. 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.
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).
Web_Services_Description_Language offers support for binding to all the Hypertext_Transfer_Protocol#Request_methods (not only GET and POST as in version 1.1)so it enables a better implementation of Representational_State_Transfer .However support for this specification is still poor in
Software_development_kit, which often offer tools only for WSDL 1.1.
Criticisms
Critics of non-RESTful Web services often complain that they are too complexhttp://www.tbray.org/ongoing/When/200x/2004/09/21/WS-Research and biased towards large software vendors or integrators, rather than open source implementations.
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 or C# code. 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 XML_Schema_Definition#XML_Schema_Definition 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.
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. At the same time there are emerging XML parsing/indexing technologies, such as
VTD-XML, that promise to address those XML-related performance issues.
Similar efforts
There are several other approaches to the set of problems that Web services attempts to address, both preceding and contemporary to it.
Java remote method invocation was one of many
middleware systems that have seen wide deployment. More ambitious efforts like
CORBA and
Distributed Component Object Model attempted to effect distributed
object oriented programming, which Web services implementations sometimes try to mimic.
More basic efforts include
XML-RPC, a precursor to SOAP that was only capable of RPC, and various forms of
HTTP usage without SOAP.
See also
Notes
External links
- W3C Web Services Activity home page
- Web Services Architecture (W3C Working Group Note)
- Secure, Reliable, Transacted Web Services (IBM/Microsoft white paper)
- Automate Web service testing, Part 3: Test a secured Web service with IBM Rational Software Architect and XMLUnit (IBM developerWorks tutorial - advanced level)
- XMethods - Collection of public Web Services
- The Performance Woe of Binary XML
- What is a WebService?
The W3C defines a
Web service (many sources also capitalize the second word, as in Web
Services) as "a software system designed to support interoperability
Machine to Machine interaction over a computer network." Web services are frequently just Web application programming interfaces that can be accessed over a network, such as the
Internet, and executed on a remote system hosting the requested services.
The W3C Web service definition encompasses many different systems, but in common usage the term refers to
Client (computing) and Server (computing) that communicate using XML messages that follow the
SOAP standard. Common in both the field and the terminology is the assumption that there is also a machine readable description of the operations supported by the
server (computing) written in the
Web Services Description Language (WSDL). The latter is not a requirement of a SOAP
endpoint, but it is a prerequisite for automated client-side code generation in the mainstream
Java (programming language) and
Microsoft .NET SOAP frameworks. Some industry organizations, such as the
WS-I, mandate both SOAP and WSDL in their definition of a Web service.
Specifications
Core specifications
The specifications that define
Web services are intentionally modular, and as a result there is no one document that contains them all. Additionally, there is neither a single, nor a stable set of specifications. There are a few "core" specifications that are supplemented by others as the circumstances and choice of technology dictate, including:
SOAP: An XML-based, extensible message envelope format with "bindings" to underlying protocols. The primary protocols are HTTP and HTTPS, although bindings for others, including
Simple Mail Transfer Protocol and
Extensible Messaging and Presence Protocol, have been written.Web Services Description Language (WSDL): An XML format that allows service interfaces to be described along with the details of their bindings to specific protocols. Typically used to generate server and client code, and for configuration.Universal Description, Discovery, and Integration (
UDDI): A protocol for publishing and discovering metadata about Web services that enables applications to find them, either at design time or runtime.
Most of these core specifications have come from
World Wide Web Consortium, including XML,
SOAP, and Web Services Description Language; UDDI comes from
OASIS (organization).
See
List of Web service specifications for a more complete listing.
Profiles
To improve interoperability of Web Services, the
WS-I publishes profiles. A profile is a set of core specifications (SOAP, WSDL, ...) 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-*. 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-Reliability: An OASIS (organization) standard protocol for reliable messaging between two Web services.WS-ReliableMessaging A protocol for reliable messaging between two Web services, issued by
Microsoft, BEA Systems and IBM it is currently being standardized by the OASIS organization http[WS-Addressing: A way of describing the address of the recipient (and sender) of a message, inside the SOAP message itself.
WS-Transaction: A way of handling transactions.
Some of these additional specifications have come from the World Wide Web Consortium. 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. 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 (organization) has standardized many Web service extensions, including Web Services Resource Framework and
WSDM.
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
Remote procedure call Web services present a distributed function (or method) call interface that is familiar to many developers. 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 Loose coupling, because it was often implemented by mapping services directly to language-specific function or method calls... Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the
WS-I Basic Profile.
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. 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.
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).
Web_Services_Description_Language offers support for binding to all the Hypertext_Transfer_Protocol#Request_methods (not only GET and POST as in version 1.1)so it enables a better implementation of Representational_State_Transfer .However support for this specification is still poor in Software_development_kit, which often offer tools only for WSDL 1.1.
Criticisms
Critics of non-RESTful Web services often complain that they are too complexhttp://www.tbray.org/ongoing/When/200x/2004/09/21/WS-Research and biased towards large software vendors or integrators, rather than open source implementations.
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 or C# code. 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 XML_Schema_Definition#XML_Schema_Definition 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.
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. At the same time there are emerging XML parsing/indexing technologies, such as VTD-XML, that promise to address those XML-related performance issues.
Similar efforts
There are several other approaches to the set of problems that Web services attempts to address, both preceding and contemporary to it.
Java remote method invocation was one of many
middleware systems that have seen wide deployment. More ambitious efforts like CORBA and Distributed Component Object Model attempted to effect distributed object oriented programming, which Web services implementations sometimes try to mimic.
More basic efforts include
XML-RPC, a precursor to SOAP that was only capable of RPC, and various forms of HTTP usage without SOAP.
See also
Notes
External links
- W3C Web Services Activity home page
- Web Services Architecture (W3C Working Group Note)
- Secure, Reliable, Transacted Web Services (IBM/Microsoft white paper)
- Automate Web service testing, Part 3: Test a secured Web service with IBM Rational Software Architect and XMLUnit (IBM developerWorks tutorial - advanced level)
- XMethods - Collection of public Web Services
- The Performance Woe of Binary XML
- What is a WebService?
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