Application Development: Web Services Part 1

Web Services

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

What are Web Services?

• 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.

Service-Oriented Architecture (SOA)

• 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.

Web Service Standards

• 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.

Relationships between Web Service Standards

• 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.

Web Service Description Language (WSDL)

• 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.

WSDL Supplementary Constructs

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

SOAP

• SOAP is a standard message format for hosting RPC and document-centric data.
• SOAP facilitates synchronous and asynchronous data exchange models.

SOAP Message Structure

• 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

• 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.