The following is the Web Services stack from WebServices.Org.
Service Negotiation
The business logic process starts at the Services Negotiation layer (the top) with, say, two trading partners negotiating and
agreeing on the protocols used to aggregate Web Services. This layer is also referred to as the Process Definition layer, covering
document, workflow, transactions, and process flow.
Workflow, Discovery, Registries
The stack then moves to the next layer to establish workflow processes using Web Services Flow Language (WSFL) and
MS XLANG, which is an XML language to describe workflow processes and spawn them. Microsoft previously achieved
recognition for WSDL by working with IBM. History may repeat itself since IBM now has a similar technology to XLANG.
In April 2001, IBM published WSFL. Gartner expected IBM and Microsoft to jointly agree to submit a proposal to W3C
to combine XLANG and WSFL by the end of 2001. Yet, the W3C Web site has not indicated whether it has received the
proposal for consideration. If it did, the proposal has not yet been posted on the Web site (February 2002).
WSFL specifies how a Web Service is interfaced with another. With it, you can determine whether the Web Services should
be treated as an activity in one workflow or as a series of activities. While WSFL complements WSDL (Web Services
Definition Language) and is transition-based, XLANG is an extension of WSDL and block-structured based. WSFL supports
two model types: flow and global models. The flow model describes business processes that a collection of Web
Services needs to achieve. The global model describes how Web Services interact with one another. XLANG, on the other
hand, allows orchestration of Web Services into business processes and composite Web Services. WSFL is strong on model
presentation while XLANG does well with the long-running interaction of Web Services.
You may declare a Web Service as private, meaning that it cannot expose details of what it does to public applications. You
can create Web Services with the WebMethod Attribute in Visual Basic.NET, or with EJB wrappers for existing J2EE applications
in either the Internet (public) or intranet (private) environment. You may declare them as public or private methods
when you code.
Among the software supporting WSFL is IBM MQ Series Workflow (now known as WebSphere Process Manager) that
automates business process flows, optimizes Enterprise Application Integration (EAI) with people workflow, provides scalability,
and complies with the Workflow Coalition and multi-platform capabilities. MS XLANG is the language implemented
in BizTalk.
Web Services that can be exposed may, for example, get information on credit validation activities from a public directory
or registry, such as Universal Description, Discovery and Integration (UDDI). The ebXML, E-Services Village, BizTalk.org,
and xml.org registries and Bowstreet's (a stock service brokerage) Java-based UDDI (jUDDI) are other directories that
could be used with UDDI in conjunction with Web Services for business-to-business (B2B) transactions in a complex EAI
infrastructure under certain conditions. Web Services is still primarily an interfacing architecture, and needs an integration
platform to which it is connected. Such an integration platform would cover the issue of integrating an installed base of
applications that cannot work as Web Services yet.
The first release of UDDI's Business Registry became fully operational in May 2001, enabling businesses to register and discover
Web Services via the Internet. Its original intent was to enable electronic catalogues in which businesses and services
could be listed. The UDDI specification defines a way to publish and discover information about services. In November
2001, the UDDI Business Registry v2 beta became publicly available.
Hewlett Packard Company, IBM, Microsoft, and SAP launched beta implementation of their UDDI sites that have conformed
to the latest specification, including enhanced support for deploying public and private Web Service registries, and
the interface (SOAP/HTTP API) that the client could use to interact with the registry server. In addition to the public UDDI
Business Registry sites, enterprises can also deploy private registries on their intranet to manage internal Web Services using
the UDDI specification. Access to internal Web Service information may also be extended to a private network of business
partners.
Service Description Language
As you move further down the stack, you need WSDL to connect to a Web Service. This language is an XML format for
describing network services. With it, service requesters can search for and find the information on services via UDDI,
which, in turn, returns the WSDL reference that can be used to bind to the service.
Web Service Conversational Language (WSCL) helps developers use the XML Schema to better describe the structure of
data in a common format (say, with new data types) the customers, Web browsers, or indeed any XML enabled software
programs can recognize. This protocol can be used to specify a Web Service interface and to describe service interactions.
Messaging
Now, we get to the Messaging layer in the stack where SOAP acts as the envelope for XML-based messages, covering message
Web Services as the work progresses (say, from customer order to shipping product out of the warehouse).
packaging, routing, guaranteed delivery and security. Messages are sent back and forth regarding the status of various
Transport Protocols
When a series of messages completes its rounds, the stack goes to its last layer: the transport layer using Hypertext Transfer
Protocol (HTTP), Secure HTTP (HTTPS), Reliable HTTP (HTTPR) File Transfer Protocol (FTP) or Standard Mail Transfer
Protocol (SMTP). Then, each Web Service takes a ride over the Internet to provide a service requester with services or give
a status report to a service provider or broker.
Business Issues
Finally, the Business Issues row in the table lists other key areas of importance to the use and growth of Web Services.
Without consideration to these points, Web Services could quickly become objects of ridicule.
|
Layer
|
Example
|
|
Service
Negotiation
|
Trading
Partner Agreement
|
|
Workflow,
Discovery, Registries
|
UDDI, ebXML
registries, IBM WSFL, MS XLANG
|
|
Service
Description Language
|
WSDL/WSCL
|
|
Messaging
|
SOAP/XML
Protocol
|
|
Transport
Protocols
|
HTTP, HTTPS,
FTP, SMTP
|
|
Business
Issues
|
Management,
Quality of Service, Security, Open Standards
|
