Web service

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A web service (WS) is either:

In a web service, a web technology such as HTTP is used for transferring machine-readable file formats such as XML and JSON.

Contents

In practice, a web service commonly provides an object-oriented web-based interface to a database server, utilized for example by another web server, or by a mobile app, that provides a user interface to the end-user. Many organizations that provide data in formatted HTML pages will also provide that data on their server as XML or JSON, often through a Web service to allow syndication. Another application offered to the end-user may be a mashup, where a Web server consumes several Web services at different machines and compiles the content into one user interface.

Web services (generic)

Asynchronous JavaScript and XML

Asynchronous JavaScript and XML (AJAX) is a dominant technology for Web services. Developing from the combination of HTTP servers, JavaScript clients and Plain Old XML (as distinct from SOAP and W3C Web Services), now it is frequently used with JSON as well as, or instead of, XML.

REST

Representational State Transfer (REST) is an architecture for well-behaved Web services that can function at Internet scale.

In a 2004 document, the W3C sets following REST as a key distinguishing feature of Web services:

We can identify two major classes of Web services:

  • REST-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of stateless operations; and
  • arbitrary Web services, in which the service may expose an arbitrary set of operations.
    — W3C, Web Services Architecture [1]

There are a number of Web services that use markup languages:

Web API

A Web API is a development in Web services where emphasis has been moving to simpler representational state transfer (REST) based communications. [2] Restful APIs do not require XML-based Web service protocols (SOAP and WSDL) to support their interfaces.

W3C Web services

In relation to W3C Web services, the W3C defined a Web service as:

A web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the web service in a manner prescribed by its description using SOAP-messages, typically conveyed using HTTP with an XML serialization in conjunction with other web-related standards.

— W3C, Web Services Glossary [3]

W3C Web Services may use SOAP over HTTP protocol, allowing less costly (more efficient) interactions over the Internet than via proprietary solutions like EDI/B2B. Besides SOAP over HTTP, Web services can also be implemented on other reliable transport mechanisms like FTP. In a 2002 document, the Web Services Architecture Working Group defined a Web services architecture, requiring a standardized implementation of a "Web service."

Explanation

Web services architecture: the service provider sends a WSDL file to UDDI. The service requester contacts UDDI to find out who is the provider for the data it needs, and then it contacts the service provider using the SOAP protocol. The service provider validates the service request and sends structured data in an XML file, using the SOAP protocol. This XML file would be validated again by the service requester using an XSD file. Webservices-en.svg
Web services architecture: the service provider sends a WSDL file to UDDI. The service requester contacts UDDI to find out who is the provider for the data it needs, and then it contacts the service provider using the SOAP protocol. The service provider validates the service request and sends structured data in an XML file, using the SOAP protocol. This XML file would be validated again by the service requester using an XSD file.

The term "Web service" describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet Protocol backbone. XML is the data format used to contain the data and provide metadata around it, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI lists what services are available.

A Web service is a method of communication between two electronic devices over a network. It is a software function provided at a network address over the Web with the service always-on as in the concept of utility computing.

Many organizations use multiple software systems for management.[ citation needed ] Different software systems often need to exchange data with each other, and a Web service is a method of communication that allows two software systems to exchange this data over the Internet. The software system that requests data is called a service requester, whereas the software system that would process the request and provide the data is called a service provider .

Different software may use different programming languages, and hence there is a need for a method of data exchange that doesn't depend upon a particular programming language. Most types of software can, however, interpret XML tags. Thus, Web services can use XML files for data exchange.

Rules for communication with different systems need to be defined, such as:

All of these rules for communication are defined in a file called WSDL (Web Services Description Language), which has a .wsdl extension. (Proposals for Autonomous Web Services (AWS) seek to develop more flexible Web services that do not rely on strict rules. [a] )

A directory called UDDI (Universal Description, Discovery, and Integration) defines which software system should be contacted for which type of data. So when one software system needs one particular report/data, it would go to the UDDI and find out which other systems it can contact for receiving that data. Once the software system finds out which other systems it should contact, it would then contact that system using a special protocol called SOAP (Simple Object Access Protocol). The service provider system would first validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.

Automated design methods

Web services in a service-oriented architecture. SOA Detailed Diagram.png
Web services in a service-oriented architecture.

Automated tools can aid in the creation of a Web service. For services using WSDL, it is possible to either automatically generate WSDL for existing classes (a bottom-up model) or to generate a class skeleton given existing WSDL (a top-down model).

Criticism

Critics of non-RESTful Web services often complain that they are too complex [8] and based upon large software vendors or integrators, rather than typical open source implementations.

There are also concerns about performance due to Web services' use of XML as a message format and SOAP/HTTP in enveloping and transporting. [9]

Regression testing of Web services

Functional and non-functional testing of Web services is done with the help of WSDL parsing. Regression testing is performed by identifying the changes made to upgrade software. Web service regression testing needs can be categorized in three different ways, namely, changes in WSDL, changes in the code, and selective re-testing of operations. We can capture the above three needs in three intermediate forms of Subset WSDL, [7] namely, Difference WSDL (DWSDL), Unit WSDL (UWSDL), and Reduced WSDL (RWSDL), respectively. These three Subset WSDLs are then combined to form Combined WSDL (CWSDL) that is further used for regression testing of the Web service. This will help in Automated Web Service Change Management (AWSCM), [10] by performing the selection of the relevant test cases to construct a reduced test suite from the old test suite. [11]

Web services testing can also be automated using several test automation tools like SoapUI, Oracle Application Testing Suite (OATS), [12] [13] Unified Functional Testing, Selenium, etc.

Web service change management

Work-related to the capture and visualization of changes made to a Web service. Visualization and computation of changes can be done in the form of intermediate artifacts (Subset WSDL). [7] The insight on the computation of change impact is helpful in testing, top-down development and reduce regression testing. AWSCM [10] is a tool that can identify subset operations in a WSDL file to construct a subset WSDL.

Discovering and Searching for Web Services

While UDDI was intended to serve as a service directory and become the means to discovering web services, many vendors discontinued their UDDI solutions or repositories between 2005-2008, including Microsoft, SAP, IBM, among others. [14] [15] A key study published in WWW2008 Conference (Beijing, China) [16] presented the state of SOAP-based web services and concluded that only 63% of the available SOAP-based web services at the time of the study were actually active or can be invoked. The study also found that search engines were becoming an ideal source for searching for web services compared to that of service registries like the UDDI due its design complexity. [17]

See also

Notes

  1. ↑ Compare: Oya 2008, "Under the current Web Services, […] stakeholder systems must follow the predefined rules for a particular business service including those about business protocols to send/receive messages and about system operation. […] More flexible mechanism is desired where freely built and autonomously running systems can exchange business messages without pre-agreed strict rules. We call it Autonomous Web Services (AWS) and proposed the framework called Dynamic Model Harmonization (DMH) with its algorithm, which dynamically adjusts different business process models between systems […]." [4]

Related Research Articles

In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space, which is written as if it were a normal (local) procedure call, without the programmer explicitly writing the details for the remote interaction. That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. This is a form of client–server interaction, typically implemented via a request–response message passing system. In the object-oriented programming paradigm, RPCs are represented by remote method invocation (RMI). The RPC model implies a level of location transparency, namely that calling procedures are largely the same whether they are local or remote, but usually, they are not identical, so local calls can be distinguished from remote calls. Remote calls are usually orders of magnitude slower and less reliable than local calls, so distinguishing them is important.

SOAP is a messaging protocol specification for exchanging structured information in the implementation of web services in computer networks. It uses XML Information Set for its message format, and relies on application layer protocols, most often Hypertext Transfer Protocol (HTTP), although some legacy systems communicate over Simple Mail Transfer Protocol (SMTP), for message negotiation and transmission.

<span class="mw-page-title-main">Interface description language</span> Computer language used to describe a software components interface

An interface description language or interface definition language (IDL) is a generic term for a language that lets a program or object written in one language communicate with another program written in an unknown language. IDLs are usually used to describe data types and interfaces in a language-independent way, for example, between those written in C++ and those written in Java.

The Organization for the Advancement of Structured Information Standards is a nonprofit consortium that works on the development, convergence, and adoption of projects - both open standards and open source - for Computer security, blockchain, Internet of things (IoT), emergency management, cloud computing, legal data exchange, energy, content technologies, and other areas.

XForms is an XML format used for collecting inputs from web forms. XForms was designed to be the next generation of HTML / XHTML forms, but is generic enough that it can also be used in a standalone manner or with presentation languages other than XHTML to describe a user interface and a set of common data manipulation tasks.

In software engineering, service-oriented architecture (SOA) is an architectural style that focuses on discrete services instead of a monolithic design. SOA is a good choice for system integration. By consequence, it is also applied in the field of software design where services are provided to the other components by application components, through a communication protocol over a network. A service is a discrete unit of functionality that can be accessed remotely and acted upon and updated independently, such as retrieving a credit card statement online. SOA is also intended to be independent of vendors, products and technologies.

REST is a software architectural style that was created to guide the design and development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of a distributed, Internet-scale hypermedia system, such as the Web, should behave. The REST architectural style emphasises uniform interfaces, independent deployment of components, the scalability of interactions between them, and creating a layered architecture to promote caching to reduce user-perceived latency, enforce security, and encapsulate legacy systems.

The Web Services Invocation Framework (WSIF) supports a simple and flexible Java API for invoking any Web Services Description Language (WSDL)-described service.

Web Services Discovery provides access to software systems over the Internet using standard protocols. In the most basic scenario there is a Web Service Provider that publishes a service and a Web Service Consumer that uses this service. Web Service Discovery is the process of finding suitable web services for a given task.

A web service protocol stack is a protocol stack that is used to define, locate, implement, and make Web services interact with each other. A web service protocol stack typically stacks four protocols:

XML Interface for Network Services (XINS) is an open-source technology for definition and implementation of internet applications, which enforces a specification-oriented approach.

The Windows Communication Foundation (WCF), previously known as Indigo, is a free and open-source runtime and a set of APIs in the .NET Framework for building connected, service-oriented applications.

In software architecture, a messaging pattern is an architectural pattern which describes how two different parts of an application, or different systems connect and communicate with each other. There are many aspects to the concept of messaging which can be divided in the following categories: hardware device messaging and software data exchange. Despite the difference in the context, both categories exhibit common traits for data exchange.

<span class="mw-page-title-main">Web API</span> HTTP-based application programming interface on the web

A web API is an application programming interface (API) for either a web server or a web browser. As a web development concept, it can be related to a web application's client side. A server-side web API consists of one or more publicly exposed endpoints to a defined request–response message system, typically expressed in JSON or XML by means of an HTTP-based web server. A server API (SAPI) is not considered a server-side web API, unless it is publicly accessible by a remote web application.

In computing, logging is the act of keeping a log of events that occur in a computer system, such as problems, errors or just information on current operations. These events may occur in the operating system or in other software. A message or log entry is recorded for each such event. These log messages can then be used to monitor and understand the operation of the system, to debug problems, or during an audit. Logging is particularly important in multi-user software, to have a central overview of the operation of the system.

<span class="mw-page-title-main">Web Services Description Language</span> XML-based interface description language

The Web Services Description Language is an XML-based interface description language that is used for describing the functionality offered by a web service. The acronym is also used for any specific WSDL description of a web service, which provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. Therefore, its purpose is roughly similar to that of a type signature in a programming language.

IBM WebSphere Service Registry and Repository (WSRR) is a service registry for use in a Service-oriented architecture.

gSOAP is a C and C++ software development toolkit for SOAP/XML web services and generic XML data bindings. Given a set of C/C++ type declarations, the compiler-based gSOAP tools generate serialization routines in source code for efficient XML serialization of the specified C and C++ data structures. Serialization takes zero-copy overhead.

References

  1. ↑ "Web Services Architecture § Relationship to the World Wide Web and REST Architectures". W3C . Retrieved 11 November 2017.
  2. ↑ Benslimane, D.; Dustdar, S.; Sheth, A. (2008). "Services Mashups: The New Generation of Web Applications". IEEE Internet Computing . 10 (5): 13–15. doi:10.1109/MIC.2008.110. S2CID   8124905.
  3. ↑ "Web Services Glossary § Web service". W3C . 11 February 2004. Retrieved 24 January 2017.
  4. ↑ Oya, Makoto (2008-09-02). "Autonomous Web Services Based on Dynamic Model Harmonization". In Oya, Makoto; Uda, Ryuya; Yasunobu, Chizuko (eds.). Towards Sustainable Society on Ubiquitous Networks: The 8th IFIP Conference on E-Business, E-Services, and E-Society (I3E 2008), September 24 – 26, 2008, Tokyo, Japan. IFIP Advances in Information and Communication Technology. Vol. 286. Springer Science & Business Media (published 2008). p. 139. ISBN   9780387856902 . Retrieved 2015-08-19.
  5. ↑ "Creating bottom-up Web services". Eclipse . Retrieved 11 November 2017.
  6. ↑ "Creating top-down Web services". Eclipse . Retrieved 11 November 2017.
  7. 1 2 3 Chaturvedi, Animesh (2014). Subset WSDL to Access Subset Service for Analysis. 2014 IEEE 6th International Conference on Cloud Computing Technology and Science. p. 688. doi:10.1109/CloudCom.2014.149. ISBN   978-1-4799-4093-6.
  8. ↑ Bray, Tim (2004-10-28). "WS-Pagecount". TBray.org. Retrieved 2011-04-22.
  9. ↑ Gray, N. A. B. (2005). "Performance of Java Middleware – Java RMI, JAX-RPC, and CORBA". University of Wollongong : 31–39. The results presented in this paper show that the nature of response data has a greater impact on relative performance than has been allowed for in most previous studies.
  10. 1 2 Chaturvedi, Animesh (2014). Automated Web Service Change Management AWSCM - A Tool. 2014 IEEE 6th International Conference on Cloud Computing Technology and Science. p. 715. doi:10.1109/CloudCom.2014.144. ISBN   978-1-4799-4093-6.
  11. ↑ Chaturvedi, Animesh; Gupta, Atul (2013). A tool-supported approach to perform efficient regression testing of Web services. 2013 IEEE 7th International Symposium on the Maintenance and Evolution of Service-Oriented and Cloud-Based Systems. p. 50. doi:10.1109/MESOCA.2013.6632734. ISBN   978-1-4673-4889-8.
  12. ↑ Oracle Application Testing Suite
  13. ↑ Web Services Testing using Oracle Application Testing Suite
  14. ↑ Krill, Paul (2005-12-16). "Microsoft, IBM, SAP discontinue UDDI registry effort". InfoWorld. Retrieved 2022-05-28.
  15. ↑ QuinnRadich (27 April 2021). "Removal of UDDI Services from Server Operating System – Win32 apps". docs.microsoft.com. Retrieved 2022-05-28.
  16. ↑ "WWW2008 – WWW 2008: 17th International World Wide Web Conference (Welcome)". Archived from the original on 2022-10-04. Retrieved 2022-05-28.
  17. ↑ Al-Masri, Eyhab; Mahmoud, Qusay H. (2008-04-21). "Investigating web services on the world wide web". Proceedings of the 17th international conference on World Wide Web. WWW '08. New York, NY, USA: Association for Computing Machinery. pp. 795–804. doi:10.1145/1367497.1367605. ISBN   978-1-60558-085-2. S2CID   12570844.
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