Web Services for Clients

Abstract

Introduction

Successful Practices

• A variety of user agents implement standards which can interact with a variety of servers complying with the same standards.
• • Browsers implement standard markup languages, encouraging open implementation of web content and service applications
  • ECMAScript is almost universally accepted for describing logic and processing in web browsers
  • Transports (such as HTTP/S, etc.) are layered away from the message structures (HTML etc.) and envelopes (MIME, etc.).
• Instant messaging and other peer services are becoming popular
• Servers and user agents exchange data in XML messages using HTTP request response mechanisms
• URIs, advertisements, search engines, and directories help users locate services they are interested in

Less-Successful Practices

• Java, ActiveX, and other traditional programming languages have failed to revolutionize the user agent and are not currently strategic to most web services
• Cookies associate server-side state with user agent sessions
• Data and presentation have generally not been separable in user agents
• • Data must be resynchronized as each page is visited, even though the same form could apply to multiple data sets and the same data set to multiple forms.
  • The web server must artificially partition, serve, and commingle the UI and data as distinct HTML pages.
  • Sensitive user data such as credit card numbers is kept on the server so it can be automatically filled in
  • The client is limited to interacting with a single server that provided the UI
  • Support for alternative display devices is difficult at best
• CORBA and DCOM produce proprietary services because they tie client and server implementations and environments too tightly
• Single best practices for exchanging data messages have not emerged
• Standard business objects, models, and directories of services have not emerged

W3C Activities

• XForms separates presentation from content, starting to make the following possible:
• • Permits data and UI to be independently activated and updated.
  • Data may be independently requested and served
  • Sensitive or large data stores may be maintained by the user agent
  • Independent requests may be serviced by different servers and merged in the client
  • The new data-centric services encouraged by XForms may permit servers to more easily interact with other servers
  • Alternative UIs can more easily be adapted to interact with the same data services
• XMLP defines packaging of XML message fragments and remote procedure calls
• • This gets service writers thinking in terms of exchanging XML messages and marshaling programming objects
  • This may yield a useful compound processing model for messages that need more than the existing post and response of XML messages on HTTP defines
  • Remote procedure calls lack specific portable and interoperable bindings to languages ala CORBA and DCOM, which can preclude portability of scripted content between different browsers
  • Without message-based standards, remote procedure calls may tend to hardwire implementations (and implementation environments where no portable bindings have been created)
  • The user agents cannot be expected to use these services portably without at least a standard ECMAScript binding
• XPath, XMLQuery, XSLT, XMLSchema, etc. provide declarative data querying, transformation and validation.

Netscape / AOL Suggests Standardization Efforts

• Portable XMLP bindings in ECMAScript
• • Standardized remote service discovery APIs
  • Service invocation APIs
  • Marshaling and unmarshaling between objects and messages for SOAP encoding and for arbitrarily customized encodings that may be implemented in Javascript
  • Attaching arbitrary data to the service request
  • Validating inbound requests
  • Associating inbound requests with service scripts
• Service descriptions
• • RPC interface based message descriptions
  • Message-based service descriptions
  • Evolution of service contracts
  • Methods for publishing and discovering services
• Peer to peer services
• • Transports for carrying service messages via instant and email messages
  • Scope and security of downloaded service scripts invoked on inbound messages
  • Processing models for client services
• Persistence to safely maintain state on the client, where state may be expressed in the form of XML documents, fragments, or messages