Ten basic web services concepts
Here are ten vital concepts for understanding what's what in web services. All definitions are drawn from Loosely Coupled's online glossary. For a full listing of definitions available in the glossary, see the A-Z index.
(HyperText Transfer Protocol) The Web's communication standard. Stabilized at HTTP/1.1, it defines the universal mechanism for exchanging application-level messages between Web devices. All web services run over HTTP.
The shared global computing network. A network based on standards including Internet Protocol (IP), Simple Mail Transfer Protocol (SMTP) and the Domain Name System (DNS), which enables global communications between all connected computing devices. It provides the platform for web services and the WorldWide Web.
The friction-free linking enabled by web services (or any SOA). Loosely coupled services, even if they use incompatible system technologies, can be joined together on demand to create composite services, or disassembled just as easily into their functional components. Participants must establish a shared semantic framework to ensure messages retain a consistent meaning across participating services.
(Service Oriented Architecture) A system for linking resources on demand. In an SOA, resources are made available to other participants in the network as independent services that are accessed in a standardized way. This provides for more flexible loose coupling of resources than in traditional systems architectures.
(Simple Object Access Protocol) The standard for web services messages. Based on XML, SOAP defines an envelope format and various rules for describing its contents. Seen (with WSDL and UDDI) as one of the three foundation standards of web services, it is the preferred protocol for exchanging web services, but by no means the only one; proponents of REST say that it adds unnecessary complexity.
(Universal Description, Discovery and Integration protocol) A directory model for web services. UDDI is a specification for maintaining standardized directories of information about web services, recording their capabilities, location and requirements in a universally recognized format. Seen (with SOAP and WSDL) as one of the three foundation standards of web services, UDDI is currently the least used of the three.
(Uniform Resource Identifier) The address of an Internet resource. A URI is the unique name used to access the resource. It is not necessarily a specific file location (it may be a call to an application or a database, for example), which is why it is preferred over the similar acronym URL (Uniform Resource Locator).
Automated resources accessed via the Internet. Web services are software-powered resources or functional components whose capabilities can be accessed at an internet URI. Standards-based web services use XML to interact with each other, which allows them to link up on demand using loose coupling.
(Web Services Description Language) The standard format for describing a web service. Expressed in XML, a WSDL definition describes how to access a web service and what operations it will perform. Usually pronounced "whizz-dul" (to rhyme with 'whistle'), WSDL is seen (with SOAP and UDDI) as one of the three foundation standards of web services.
(eXtensible Markup Language) The data tagging language of web services. XML is not so much a language as a standardized set of rules for adding structure to any form of data using a system of markup tags. Anyone can create their own markup vocabulary (called an XML Schema), and XML ensures that the structure will be intelligible to anyone else who consults the XML Schema document. More importantly, referring to an XML Schema enables XML-aware software to automatically manipulate the data without needing advance knowledge of the structure.
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