AS2 (Applicability Standard 2) is the RFC standard (RFC 4130) that enables vendor applications to communicate EDI or other business-to-business data (such as XML) over the Internet using HTTP, a standard used by the World Wide Web.
The AS2 standard is one of the most widely adopted messaging standards in the world. With retailers, consumer products goods, hard-lines, insurance, financial services, petroleum and government industries (to name a few) adopting AS2, the critical financial information that flows over AS2 messaging represents billions of dollars each year.
Applicability Standard 3
AS3 (Applicability Standard 3) is the draft specification standard that enables vendor applications to communicate EDI (or other data such as XML) over the Internet using File Transfer Protocol (FTP).
AS3 is not the next version of AS2 as it offers its own unique features and provides security for the transport payload through digital signatures and data encryption. It also ensures reliable delivery through the use of receipts. AS3 only specifies how to transport data and not how to validate or process it. As with both AS1 and AS2, AS3 was developed as part of the IETF EDI-INT Work Group.
Applicability Standard 4
AS4 (Applicability Statement 4) jump-starts ebMS v3 implementations by constraining the options for vendors to implement, as well as provides some specific guidance for using Web services as a secure, document-agnostic B2B messaging platform. The Web services landscape lacks a B2B message specification that has the simplicity and elegance of AS2, and the simplification of Web services for B2B will breed an environment whereby the likelihood for interoperability becomes achievable. With simplicity and interoperability as attainable characteristics, widespread adoption of a standardized approach to Web services for B2B messaging can become a reality. The AS4 Profile provides the marketplace an entry-level on-ramp to begin utilizing its internal SOA platforms for external B2B messaging while taking on some of the more complicated aspects of Web services.