SOA model - The Triangle of Roles

To understand more about SOA, we look at the three major roles within the architecture. This diagram shows this three roles: Service provider, requester and Discovery Facility.

Service provider implements the service and makes it available on the network.

A requester is a consumer can find the required service via the Discovery Facilities. Once discovered the requester can utilizes the service by opening a network connection and sending an request message.

A registry provides a central place where developers can publish new services or find existing ones. It therefore serves as a centralized clearinghouse for companies and their services.

Web Services (WS) is used to implement SOA and the following further describe WS:

• It is a software application identified by a URI
• Whose Interface and binding are capable of being defined, described and discovered by XML artifacts.
• It supports direct interactions with other software applications using XML based messaging via Internet based protocols

We need some basic standards:

1. Message Protocol:
Web Services consist of a set of protocols and standards. The participants of the Web Services communicate using the Message protocol over the network. This message uses Extensible Mark-up Language (XML). Simple Object Access Protocol (SOAP) is the standard used for the message protocol.

2. Web Descriptions:
The interface of the Service Provider is described using a standard called Web Services Description Language (WSDL). WSDL is a standard for describing the wire format of the messages that are carried by SOAP envelopes. A WSDL file is an XML document that acts as a contract for a Web service. It can be used by Service Requester of that Web service as a guide for creating and validating the XML payloads delivered to and received from that service.

3. Publish and Discovery:
Publish and Discovery is provided by a Service Broker and this repository can be implemented using the Universal Description, Discovery and Integration (UDDI) standard. UUDI provides a registry for businesses to publish their services and service requesters can used this registry to query or discover required services. UDDI provides information for machine to setup and instantiate a session easily with the service provider.