which collectively are referred to as "the
submission". We request the submission be known as the "WIDL"
submission.
Abstract
This document provides the specification for the Web
Interface Definition Language (WIDL), a metalanguage that implements a
service-based architecture over the document-based resources of the World Wide
Web. WIDL is an application of the eXtensible Markup Language (XML); it allows
interactions with Web servers to be defined as functional interfaces that can
be accessed by remote systems over standard Web protocols, and provides the
structure necessary for generating client code in languages such as Java, C/C++,
COBOL, and Visual Basic. WIDL enables a practical and cost-effective means for
diverse systems to be rapidly integrated across corporate intranets, extranets,
and the Internet.
1. Introduction
The World Wide Web is providing millions of end-users access
to ever-increasing volumes of information. While the Web initially served
browsers static documents, the resources of legacy systems, relational
databases and multi-tier applications have all been made available to the Web
browser to provide corporate users with interactive information resources
including financial services, inventory management, on-line purchasing and
package tracking.
While the Web has achieved the extraordinary feat of
providing ubiquitous accessibility to end-users, it has in many cases
reinforced manual inefficiencies in business processes as repetitive tasks are
required to transcribe or copy and paste data from browser windows into desktop
and corporate applications. This is as true of Web data provided by remote
business units and external (i.e. partner or supplier) organizations as it is
of Web data accessible from both public and subscription based Web sites. The
problem of direct access to Web data from within business applications has been
largely ignored.
The purpose of the Web Interface Definition Language (WIDL)
is to enable automation of all interactions with HTML/XML documents and forms,
providing a general method of representing request/response interactions over
standard Web protocols, and allowing the Web to be utilized as a universal
integration platform.
A central feature of WIDL is that programmatic interfaces
can be defined and managed for data (HTML, XML or text files) and services
(CGI-bin, database, or other back end systems) that are not under the direct
control of programs that require such access. WIDL definitions can be
co-located with client programs, centrally managed in a client/server
architecture, or referenced directly from HTML/XML documents.
WIDL defintions provide a mapping between Web resources and
applications written in conventional programming languages such as C/C++,
COBOL, Visual Basic, Java, JavaScript, etc., enabling automatic and structured
Web access by compatible client programs, including mainstream business
applications, desktop applications, applets, Web agents, and server-side Web
programs (CGI, etc.).
Automatic means that complex interactions with Web servers
do not require human intervention; programs can request Web data and services
by making local calls to functions which encapsulate standard Web access
protocols and utilize WIDL definitions to provide naming services, change
management, error handling, condition processing and intelligent data binding.
Structured means that Web data and services are described as
interfaces with well defined input and output variables.
Standard Web access protocols means HTTP and HTTPS.
Compatible means any program that both utilizes WIDL
definitions to define the location of Web services and the structure of data
that is returned by standard HTTP and HTTPS requests, and allows WIDL
definitions to be managed locally, centrally, or by individual service
providers.
WIDL describes business objects on the Web, providing the
basis for a common API across Web servers, legacy systems, databases, and middleware
infrastructures, and effectively transforming the Web from an access medium
into an integration platform.
This document provides a complete description of the Web
Interface Definition Language (WIDL).
2. Benefits of WIDL
A major part of the value of an Interface Defintion Language
(IDL) is that it can define services offered by applications in an abstract but
highly usable fashion. WIDL brings to the Web many of the features of IDL
concepts that have been implemented in distributed computing and transaction
processing platforms including DCE, and CORBA.
2.1 Business-to-Business Integration
WIDL makes it easy for organizations to automate business
transactions with customers and suppliers. WIDL describes and automates interactions
with services hosted by Web servers on intranets, extranets and the Internet;
it transforms the Web into a standard integration platform and provides a
universal API for all Web-enabled systems.
Using HTML, XML, HTTP and HTTPS as corporate standards glue,
WIDL requires only that target systems be Web-enabled. There are hundreds of
products in the market today which Web-enable existing systems, from mainframes
to client/server applications. The use of standard Web technologies empowers
various IT departments to make independent technology selections. This has the
effect of lowering both the technical and 'political' barriers that have
typically derailed cross-organizational integration projects.
A number of analysts have already warned that proprietary
e-commerce platforms could lock suppliers into relationships by forcing them to
integrate their systems with one infrastructure for business-to-business
integration, making it costly for them to switch to or integrate with other
partners who have selected alternate e-commerce platforms. Buyer-supplier
integration issues involve many-to-many relationships, and demand a standard
platform for functional integration and data exchange.
A service defined by WIDL is equivalent to a function call
in standard programming languages. At the highest level, WIDL files describe
the locations (URLs) of services, input parameters to be submitted (via Get or
Post methods) to each service, conditions for successful processing, and output
parameters to be returned by each service.
WIDL provides the following features:
A browser is not required to drive Web applications
WIDL definitions are dynamically interpreted and can be
centrally managed
Client applications are insulated from changes in service
locations and data extraction methods
Developers are insulated from network programming concerns
Application resources can be integrated through firewalls
and proxies
WIDL can be used to describe interfaces and services for:
Static documents (HTML, XML, and plain text files)
Dynamically generated documents (HTML, XML, and plain text
files)
HTML forms
URL directory structures
WIDL can be used:
to automate interactions with Web servers
for both on-demand and scheduled extraction of targeted Web
data
to aggregate data from a number of Web sources
to chain services across multiple Web sites
to rapidly integrate Web resources with traditional
application development languages and environments
WIDL has the ability to specify conditions for successful
processing, and error messages to be returned to calling programs. Conditions
further enable services to be defined that span multiple documents.
2.2 Change Management
One of WIDL's most significant benefits is its ability to
insulate client programs from changes in the format and location of Web
documents. Unlike the way CORBA and DCE IDL are normally used, WIDL is
interpreted at runtime; as a result, service URLs, object references in
variables, definitions of document regions, success/failure conditions, and
directives for service chaining can all be administered without requiring
modification of client code. This usage model supports
application-to-application linkages that are far more robust and maintainable
than if they were coded by hand.
There are three models for WIDL management:
client side - where WIDL files are co-located with a client
program
naming service - where WIDL definitions are centrally
managed and referenced via directory services, i.e. LDAP
server side - where WIDL files are referenced by, co-located
with, or embedded within Web documents.
WIDL does not require that existing Web resources be
modified in any way. Flexible management models allow organizations to describe
and integrate Web sites that are uncontrolled, as well as to provide their
business partners with interfaces to services that are controlled. The ability
to seamlessly migrate from independent to shared management eases the
transition from informal to formal business-to-business integration.
2.3 Language Bindings
The primary purpose of WIDL is integration of Web resources
with corporate business applications. In much the same way that DCE or CORBA
IDL is used to generate code fragments, or 'stubs', to be included in
application development projects, WIDL provides the structure necessary for
generating client code in languages such as C/C++, Java, COBOL, and Visual
Basic. Developers can thus be insulated from the need to understand both
HTML/XML parsing and Web protocols. This capability enables the existing skills
of innumerable programmers to be rapidly leveraged in the utilization of Web
based resources.
3. Object Model References
Many of the features of WIDL require a capability to
reliably identify and extract specific data elements from Web documents.
Various mechanisms for accessing elements of HTML and/or XML documents have
been defined, such as the Javascript Page Object Model, the Document Object
Model, and XLL XPointers. WIDL does not define or determine a mechanism for
accessing document data, but rather allows an object model referencing
mechanism to be specified on a per-interface basis.
The following capabilities are desirable for accessing
elements of Web documents:
HTML Parsing
XML Parsing
Text Pattern Matching
Object referencing mechanisms would ideally support both
parsing and pattern matching. Pattern matching extracts data based on regular
expressions, and is well suited to raw text files and poorly constructed HTML
documents. Parsing, on the other hand, recovers document structure and exposes
relationships between document objects, enabling elements of a document to be
accessed with an object model.
4. WIDL Reference
The Web Interface Definition Language (WIDL) is an
application of the eXtensible Markup Language (XML); its definition consists of
the various XML elements defined in this section.
Major Elements
WIDL - defines an interface
SERVICE - child of WIDL - defines a service
BINDING - child of WIDL - defines input and output
parameters for services
Minor Elements
VARIABLE - child of BINDING - defines a variable within a
binding
CONDITION - child of BINDING - defines a condition within a
binding
REGION - child of BINDING - defines a area within a document
