Attachments in SOAP Messages

EXECUTIVE SUMMARY With more Web Services relying upon attachments to meet the business needs for sending extra business data related to the SOAP messages, choosing the right technology for using attachments in SOAP messages among ever evolving standards is possible by understanding those standards from the viewpoint of processing model, and by evaluating each of them against the requirements. INTRODUCTION Packaging as attachments in SOAP messages has become a norm in the Web Services area for any data that cannot be placed inside SOAP Envelope. In the presence of several competing standards on utilizing attachments in SOAP messages, there has been tremendous confusion about which standard to choose for scenarios with different sets of requirements. This paper describes the background for leveraging attachments in SOAP messaging, and presents a brief history and an outline of each standard. It also details the impact of attachments on security, interoperability, and performance, and lays down the guidelines on how to pick a right technology in the conclusion. Service Oriented Architecture (SOA) has been the most recent trend in building distributed enterprise applications in an open, loosely-coupled way, and it is primarily through Web Services that the visions and promises of SOA are realized in its fullness. Standards and technologies around Web Services have been evolving past the earlier infant stages and have garnered wide acceptance from the industry. At the center of Web Services is SOAP at the messaging layer that connects Services Providers and Services Consumers potentially via multiple Intermediaries that can process the SOAP messages. SOAP is an XML-based messaging protocol. It started out as a cross-platform, language-neutral Remote Procedure Call (RPC) mechanism, replacing CORBA or other distributed computing technologies. Later on, it evolved into a generic messaging mechanism that accommodates various Message Exchange Patterns (MEP) including two-way request-Attachments in SOAP Messages Page 3 response pattern for Remote Method Invocation (RMI) and one-way posting pattern for transferring complicated documents such as purchase order requests. How to package SOAP messages on the transport wire and how to interpret them at the endpoint are dictated by WSDL. Based on the syntactical and semantical definitions given in WSDL, a SOAP Body and possibly zero or multiple SOAP Headers get packaged into the SOAP Envelope. WSDL also spells out transport binding, message encoding styles, and Services endpoints. With the lessons learned from SOAP1.1, SOAP1.2 takes the standard to the next level by clarifying SOAP Header …