A web service is an application accessed by clients using XML-based protocols, such as Simple Object Access Protocol (SOAP), sent over internet protocols, such as HTTP. Clients access a web service application through its interfaces and bindings, defined using XML artifacts such as a web services Definition Language (WSDL) file.
The eXtensible Markup Language (XML) is a standard developed by the World Wide Web Consortium (W3C) and is one of the foundations on which web services are built. XML enables web services and clients to communicate with each other in a common language. XML is a simple, flexible, text-based markup language. XML data is marked using tags enclosed in angled brackets. The tags contain the meaning of the data they mark. Such markup allows different systems to easily exchange data with each other.
A Document Type Definition (DTD) or XML Schema Definition (XSD) describes the structure of an XML document. It has information on the tags the corresponding XML document can have, the order of those tags, and so forth.
XSLT, which stands for eXtensible Stylesheet Language Transformation, is used for transforming XML documents from one format to another.
Simple Object Access Protocol (SOAP) provides a common messaging format for web services. SOAP enables objects not known to one another to exchange messages. SOAP uses an XML-based data encoding format and HTTP to transport messages. SOAP is independent of both the programming language and the operational platform, and it does not require any specific technology at its endpoints
Universal Description, Discovery, and Integration (UDDI) provides a standard way to register, de-register, and look up web services. Similar to a telephone system's yellow pages, a UDDI registry's enables providers to register their services and requestors to find services. Once a requestor finds a service, the registry has no more role to play between the requestor and the provider.
Web Services Description Language (WSDL) defines a standard way to specify the details of a web service. It is a general-purpose XML schema that can specifies details of web service interfaces, bindings, and other deployment details. By having such a standard way to specify details of a service, clients who have no prior knowledge of a web service can use it.
ebXML (Electronic Business using eXtensible Markup Language) is a set of specifications that enables enterprises to conduct business over the Internet. OASIS (Organization for the Advancement of Structured Information Standards) controls the ebXML specifications.
Java APIs for XML processing (JAXP) is a vendor-neutral set of lightweight APIs for parsing or processing XML documents. JAXP enables a web service to “plug in” any conforming XML parser. If no external parser is “plugged in,” then JAXP uses its own XML parser implementation.
Java API for XML-based remote procedure calls (JAX-RPC) uses an XML-based protocol for client-server remote procedure calls . JAX-RPC enables SOAP-based interoperable and portable web services. Developers use the JAX-RPC programming model to develop SOAP-based web service endpoints, along with corresponding WSDL descriptions, and clients. A JAX-RPC based web service can interact with clients that are not based on Java. Similarly, a JAX-RPC based client can interact with a non-Java-based web service implementation.
Java API for XML registries (JAXR), a Java API for accessing business registries, has a flexible architecture that supports UDDI, and other registry specifications (such as ebXML). A JAXR client, which can be a stand-alone Java application or a Java EE component, uses an implementation of the JAXR API provided by a JAXR provider to access business registries. A JAXR provider consists of two parts: a registry--specific JAXR provider, which provides a registry-specific implementation of the API, and a JAXR pluggable provider, which implements those features of the API that are independent of the type of registry. The pluggable provider hides the details of registry-specific providers from clients.
SOAP with Attachments API for Java (SAAJ) enables developers to produce and consume messages conforming to the SOAP 1.1 specification and SOAP with Attachments note. SAAJ provides an abstraction for handling SOAP messages with attachments. Advanced developers can use SAAJ to have their applications operate directly with SOAP messages. Attachments may be complete XML documents, XML fragments, or MIME-type attachments. In addition, SAAJ allows developers to enable support for other MIME types. JAX technologies, such as JAX-RPC, internally use SAAJ to hide SOAP complexities from developers. SAAJ enables:
Synchronous request-response messaging: the client sends a message and then waits for the response.
One-way asynchronous messaging: the client sends a message and continues with its processing without waiting for a response.