Application Development: Web Services Part 1

Study Notes

Supporting interactions in web services involves human-to-human, human-to-machine, and machine-to-machine interactions.

Web services support application-to-application communication, enabling "loosely coupled" integration and minimizing effort required to build integrated applications.
Web services allow apps or programmers to find cooperative programs to accomplish a specific task, enabling rapid assembly of apps by tying together app modules.
Web services are designed to enable application modules to communicate with other application modules, providing transactional or computational services.

SOA has three main participants: Service Provider, Service Registry, and Service Requestor.
Three basic operations in SOA: Publishing Services, Discovering Services, and Binding Services.
Example: Phone technician scenario illustrating publishing, discovering, and binding services.

SOAP (Simple Object Access Protocol) is an XML-based messaging format for inter-application communication via HTTP.
WSDL (Web Service Description Language) is an XML-based language for describing web service interfaces.
UDDI (Universal Description, Discovery, and Implementation) is a mechanism for dynamic discovery of service descriptions.

UDDI is used to search for services using SOAP to access UDDI, searching with keywords.
WSDL document is downloaded from the selected service from UDDI, and the URI information is used to invoke the service using SOAP.

WSDL is an XML-based language for describing web service interfaces.
An abstract interface definition contains the interface, operations, message elements, and part elements.
A concrete interface definition contains the service, endpoint, and binding elements.

Supplementary annotations can be added to provide additional information about the service.
XSD schema information provides data type support for web service definitions.

The root envelope element contains a mandatory Body element and an optional Header element.
The Header element is used for including implementation of SOAP extensions, identification of target SOAP intermediaries, processing information, and providing supplementary meta information about the SOAP message.

UDDI is a fundamental of SOA, a mechanism for service descriptions to be discovered by potential requestors.
UDDI is a central directory that hosts service descriptions, including WSDL.
UDDI registries are organized into six primary types: Business Entities, Business Services, Specification Pointers, Service Types, Business Relationships, and Subscription.