updated draft of 2. Introduction to Web Services

All,
This is an updated draft of text for Section 2 in the new outline.
Text in curly braces is instruction and not to be included.
Andrea

2. Introduction to Web Services

This section contains a "framework" or outline for understanding
international issues in Web services.

The framework is based on the Web Services Architecture document [WSA],
which defines a service as follows: "A Web service is a software system designed 
to support interoperable machine-to-machine interaction over a network. It has 
an interface described in a machine-processable format (specifically WSDL). 
Other systems interact with the Web service in a manner prescribed by its 
description using SOAP-messages, typically conveyed using HTTP with an XML 
serialization in conjunction with other Web-related standards." {this is the 
latest from the WSA doc, but I wonder if we should include liteeral text from a 
moving target...}

There are some important standards associated with Web services. Simple
Object Access Protocol (SOAP) describes the protocol used for
communication with a Web service.

SOAP defines a two-section document structure that
conforms to XML specifications. The first part of the document is the
envelope, essentially routing instructions for the body message that
follows. The second part is the body message, which contains
information the Web service requires for processing and/or a remote
procedure call. SOAP documents can have attachments with header
information in MIME format. The SOAP document, like any XML file, may
contain a charset tag, which describes the data contained in that
particular document only. An attachment can have data in a different
charset; that charset can be specified in the MIME header Content-type.
For specifying the language of their content, SOAP documents can contain 
xml:lang tags according to the XML standard [XML]. A SOAP attachment's language 
can be indicated in the MIME header Content-language.

Web Services Description Language (WSDL) [WSDL-V12] is an XML-conformant
language used to describe the information necessary for calling and
using a Web service.

Web services can be discovered in many ways. One method is by searching a 
Universal Description, Discovery, and Integration [UDDI] registry. UDDI entries 
describe the available service and point to the Web Service Description (WSD) 
via a URI. The Web Service Description is typically written in WSDL, and it
documents the mechanics of the message exchange between a requester and
a provider.

These standards work together as shown in the following scenario:

{diagram here, modified version of the old 2.1 Overview diagram}

    1.  The requester agent locates a suitable provider agent, usually
requiring human intervention. This can be accomplished through UDDI, but
also can be accomplished through other means. For example, the URL of
the provider agent may simply have been found in an advertisement somewhere.
    2.  The provider agent makes available a WSD document, which is
likely written in WSDL.
    3.  Using the information in the WSD, the requester agent can
formulate a service request. This will be a SOAP message which is then
sent to the provider agent to be acted upon.
    4.  The provider agent after receiving the request will invoke the
service and get a response. The response can be the results of the
service or an indication that a fault occurred. Note that the
interaction between the provider agent and the service are independent
of the Web Services framework and the design is left completely to the
implementors. The primary requirement is that the provider agent in turn
be able to formulate a response to return to the requester agent. This
response must satisfy both the requirements and specifications of the
Web Services Architecture and the description of the WSD.
    5.  If the service request was successfully executed, the provider
agent will formulate a response message and send it to the requester agent.
    6.  If the service request was erroneous, or the service could not
be completed for some reason, a fault message will be sent to the
requester agent.

The internationalization issues in Web services and as illustrated in
the framework fall into several categories that are common to all Web
services, regardless of the message exchange pattern used. In the section that 
follows it is assumed that the service, provider and requester agents, and data 
structures (semantics) follow best practices in internationalization and data 
structuring. Implicit in these descriptions is the expectation that data 
structures use XML Schema types to create locale-neutral data structures.

Some services may be implemented that do not follow these strictures for
reasons having to do with legacy system implementation or other
restriction. These cases are dealt with in usage scenarios later in this
document.

{add text about MEPs and SOAP Features somewhere in this section?}

Received on Monday, 24 November 2003 21:49:32 UTC