Without prejudice to other definitions I would say that a web service is software system that allows for inter-operable machine-to-machine / application-to-application interaction over a network. This generic definitions would also help consider REST architectures to be a web service as they provide similar functionality albeit being an architectural style unlike the SOAP which is a fully defined protocol.
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, for example, Wikipedia's Export. 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 are a type of internet software that use standardized messaging protocols and are made available from an application service provider’s web server for use by a client or other web-based programs. Web services can range from major services such as storage management or customer relationship management (CRM) down to much more limited services such as the furnishing of a stock quote or the checking of bids for an auction item. The term is sometimes also referred to as application services. 

"All the standard Web Services works using following components:" ... the problem with this answer is that it suggests that web services do or must operate within the SOAP/WSDL mechanism. This is inaccurate. Representational State Transfer (REST) is another very popular paradigm for implementing web services. Some major websites have deprecated their SOAP services in favor of REST web services. – scottb Jul 7 '15 at 15:50


Synchronous or Asynchronous functionality- Synchronicity refers to the binding of the client to the execution of the service. In synchronous operations, the client will actually wait for the web service to complete an operation. An example of this is probably a scenario wherein a database read and write operation are being performed. If data is read from one database and subsequently written to another, then the operations have to be done in a sequential manner. Asynchronous operations allow a client to invoke a service and then execute other functions in parallel. This is one of the common and probably the most preferred techniques for ensuring that other services are not stopped when a particular operation is being carried out.
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Web services are used for a variety of applications, but the most common is for reusing code and connecting existing programs. The web service method can help developers segment applications into components that can be used and reused for various needs. For example, more than one program might need a conversion tool or a reporting function. This is possible due to web services’ universal communication protocols.
^ Mockapetris, P.V. (November 1987). "Domain names - concepts and facilities" (HTML). IETF Documents. IETF. doi:10.17487/RFC1034. Retrieved 24 July 2017. Relative names are either taken relative to a well known origin, or to a list of domains used as a search list. Relative names appear mostly at the user interface, where their interpretation varies from implementation to implementation, and in master files, where they are relative to a single origin domain name. The most common interpretation uses the root "." as either the single origin or as one of the members of the search list, so a multi-label relative name is often one where the trailing dot has been omitted to save typing.

Exposing Business Functionality on the network - A web service is a unit of managed code that provides some sort of functionality to client applications or end users. This functionality can be invoked over the HTTP protocol which means that it can also be invoked over the internet. Nowadays all applications are on the internet which makes the purpose of Web services more useful. That means the web service can be anywhere on the internet and provide the necessary functionality as required.


^ 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]
Now we discussed in the previous topic about WSDL and how it contains information on what the Web service actually does. But how can a client application locate a WSDL file to understand the various operations offered by a web service? So UDDI is the answer to this and provides a repository on which WSDL files can be hosted. So the client application will have complete access to the UDDI, which acts as a database containing all the WSDL files.
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, for example, Wikipedia's Export. 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.
Interoperability amongst applications - Web services allow various applications to talk to each other and share data and services among themselves. All types of applications can talk to each other. So instead of writing specific code which can only be understood by specific applications, you can now write generic code that can be understood by all applications

A web service is something that a website chooses to offer to those who wish to read, update and/or delete data from your website. You might call it a "backdoor" to your data. Instead of presenting the data as part of a webpage it is provided in a pre-determined way where some of the more popular are XML and JSON. There are several ways to communicate with a webservice, some use SOAP, others have REST'ful web services, etc.
A Web service involves a service provider and a service requester (client). Because Web services feature language transparency, it doesn’t matter whether the underlying system that provides the service is written in Java while the client is written in Perl, Python or Ruby. For example, through Web services a Windows server can interact with a Linux server or serve an application to computer desktops, laptops or smart phones and other mobile devices over the World Wide Web.
^ Mockapetris, P.V. (November 1987). "Domain names - concepts and facilities" (HTML). IETF Documents. IETF. doi:10.17487/RFC1034. Retrieved 24 July 2017. Relative names are either taken relative to a well known origin, or to a list of domains used as a search list. Relative names appear mostly at the user interface, where their interpretation varies from implementation to implementation, and in master files, where they are relative to a single origin domain name. The most common interpretation uses the root "." as either the single origin or as one of the members of the search list, so a multi-label relative name is often one where the trailing dot has been omitted to save typing.
You can find out if a domain name is available by searching at the top of this page. If the domain name you want is not available, try selecting a suggested alternative that appears or searching again. If you’re still stuck, our free guide, Bringing your business online: How to choose a domain name and more, provides some more in-depth information about domain names and helps guide you through the process.
A Web service involves a service provider and a service requester (client). Because Web services feature language transparency, it doesn’t matter whether the underlying system that provides the service is written in Java while the client is written in Perl, Python or Ruby. For example, through Web services a Windows server can interact with a Linux server or serve an application to computer desktops, laptops or smart phones and other mobile devices over the World Wide Web.
* NTT America endeavors to make the domain name availability search process reliable; however, NTT America does not guarantee availability of domain names or the accuracy or security of the WHOIS system. There are several factors that could cause a WHOIS.NET query to incorrectly display that a currently registered domain is available. Regardless, if a domain name is already registered, WHOIS.NET will not be able to register the domain or gain possession of the registration from the current registrar without the permission of the current owner. The registration process is not complete until the domain name requested by you has been registered in your name with the appropriate registry. Because there are delays in the actual registration of a domain name with the appropriate registry, NTT America is not responsible if domain names requested by you are actually registered to third parties. Registration of the domain name through NTT America is not complete until you receive the final confirmation e-mail from NTT America. All registrations through NTT America are subject to NTT America's Global Terms and Conditions.
A web service is something that a website chooses to offer to those who wish to read, update and/or delete data from your website. You might call it a "backdoor" to your data. Instead of presenting the data as part of a webpage it is provided in a pre-determined way where some of the more popular are XML and JSON. There are several ways to communicate with a webservice, some use SOAP, others have REST'ful web services, etc.
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.
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, for example, Wikipedia's Export. 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.
A great domain name is a concise, easy to type, and memorable URL that reflects your brand or your website’s subject matter. Avoid using hyphens, strings of numbers, or unnecessary words to make it easy for your visitors to remember and find your website. Remember: A great domain name is one that your visitors can type correctly on their first try.
* NTT America endeavors to make the domain name availability search process reliable; however, NTT America does not guarantee availability of domain names or the accuracy or security of the WHOIS system. There are several factors that could cause a WHOIS.NET query to incorrectly display that a currently registered domain is available. Regardless, if a domain name is already registered, WHOIS.NET will not be able to register the domain or gain possession of the registration from the current registrar without the permission of the current owner. The registration process is not complete until the domain name requested by you has been registered in your name with the appropriate registry. Because there are delays in the actual registration of a domain name with the appropriate registry, NTT America is not responsible if domain names requested by you are actually registered to third parties. Registration of the domain name through NTT America is not complete until you receive the final confirmation e-mail from NTT America. All registrations through NTT America are subject to NTT America's Global Terms and Conditions.
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