Database Reference
In-Depth Information
1. A service provider can publish the availability of its service(s) and respond to requests to use,
or alternatively, it can bind to its service(s). A
service provider
is a Network node that provides
a service interface for a software asset that manages a specific set of tasks. A service provider
node can represent the service interface for a reusable subsystem.
2. A service broker allows service providers to publish (register and categorize) themselves and
their services; a service broker also offers find mechanisms for business entities attempting
to locate appropriate services for use in a solution. A
service requestor
is a Network node
that discovers and invokes other software services to provide a business solution. Service
requestor nodes will often represent a business application component that performs remote
procedure calls to a distributed object, the service provider. In some cases, the provider
node may reside locally within an intranet, or in other cases, it could reside remotely over
the Internet. The conceptual nature of SOA leaves the networking, transport protocol, and
security details to the specific implementation.
3. A service requestor uses service brokers to find the services needed to construct a solution,
or part of a solution, and then invokes (bind to) those services offered by service providers.
The third SOA participant is that of the
service broker
; it is a Network node that acts as a
repository, yellow pages, or clearing house for software interfaces that are published by service
providers. A business entity or independent operator can represent a service broker.
These three SOA participants interact using three basic operations
publish
,
ind
, and
bind
. Service
providers publish service to a service broker. Service requestors
ind
required services using a ser-
vice broker and bind to them.
An SOA is an abstract concept. To support the use of Web Services in e-business, IBM,
Microsoft, and others are working to create a concrete Web Service
stack
that defines how to con-
struct Web-Service-based solutions. It is populated with existing and emerging standards to foster
widespread interoperability and availability:
◾
The Web Service transport layer provides the basis for communicating between Web Services;
many different transport standards can be used, all leveraging existing Internet protocol stan-
dards; the specific transport used for an interaction can be negotiated at the higher layers in
the stack.
◾
The service description layer, using an emerging XML-based standard protocol called Web
Services Description Language (WSDL), supplies descriptions of Web Service interfaces,
that is, the message and parameters that flow between interacting Web Services.
◾
The Web Service messaging layer provides a lightweight protocol for the exchange of mes-
sages between Web Services in a decentralized, distributed environment; the layer uses the
XML-based Simple Object Access Protocol (SOAP) for interactions between all service
requesters and service providers.
◾
The publication and discovery layer enables the service broker role for Web Services, and the
layer leverages the Universal Description, Discovery, and Integration (UDDI) specifications
that define XML-based service and business description format and a SOAP-based API for
a service broker.
In addition to the layers, the Web Service stack offers some
verticals
that apply across all the layers.
These verticals represent the fact that some aspects of a solution permeate all layers of the stack and
thus may impact existing formats, protocols, and APIs or require new ones:
