WSDL-like code-generation for EbXML CPA+Schemas (not EbXML message itself)

Question

Background:

A certain government-backed wholesaler of broadband services in Australia took feedback from discussion groups about how best to deliver B2B services to retail ISPs. They settled on EbXML.

Problem:

We're a very small shop (comparatively) that doesn't want to spend a lot of time going forward on integration. We're already familiar with integration of paired (inbound and outbound) SOAP services. In the past we've made use of WSDL-based code generation tooling (mostly with RPC/Literal services) where the WSDL has been descriptive and simple enough for the code generation tools to digest.

If at all possible we'd like to avoid having to hand-integrate the services with our business 'stack'. We know that the 'Interface Schemas' have been updated several times; we'd like to (as much as possible) do code and schema generation such that we can model our relationship with the supplier and the outbound/inbound messages as simple "queues" (tables) in an SQL database -- this will be our point of integration.

Starting with the outbound ("sender") SOAP web-service... it publishes a Document/Literal WSDL description of the service that seems to work correctly with various tools (e.g: wsdl2java, SoapUI) to generate the EBXML 'wrapper' messages. This says nothing about the 'payload' messages themselves which (at least for the MSH we've looked at) need to be multipart/related attachments with type of text/xml.

The 'payload' messages are defined in the provided CPA (something like bindings) and Schema (standard-looking XSD) files. The MSH itself doesn't seem to provide any external validation for the payload messages.

Question:

Is the same kind of code generation (as seen with WSDL-described SOAP web services) tooling available for EbXML CPAs/Schemas? (i.e: tools that can consume the CPA and 'payload' interface schemas and spit out java/c++/whatever, and/or something WSDL-like specific to the 'payload' interface messages and/or example messages).

If so, where do I look?

If not, are there any EbXML-specific problems that would prevent it? (I'd rather not get several weeks into a project to develop tools that are impossible to implement 'correctly' given the information at hand).

Answer 1

The MSH is payload agnostic. The payloads are not defined in the CPA, only the service and action names that are used to send the ebXML payloads are. The service and action are transmitted in the ebXML header, which is the first part of the multipart message. The payloads themselves can be xml, binary or a combination. Each payload is another part.

An MSH is responsible for tasks like:

• sending (usually asynchronous) acknowledgements for received messages
• resending messages if an acknowledgement has not been received within a certain amount of time
• ignoring duplicate messages
• assuring the order in which messages are delivered is correct

the actual behaviour is all configurable using the CPA, but a compliant MSH would support all this.

This implies that an MSH has to keep an administration of the messages it has sent and received, which is usually done in a database.

I would be surprised if you could find tooling to generate an MSH from a specific CPA. What you can find is software/components that implement a generic MSH and that can be configured with CPAs.

Assuming you don't want to build your own, look for an existing ebMS adapter. Configure it with your CPA(s). Then generate the payloads however you like and pass them to the ebMS adapter.

Google for "ebMS adapter" or "ebMS support".

Answer 2

Alas, it seems there's no specific tooling around the 'payload' messages for EbXML, spefically because EbXML doesn't regulate those messages.

However, the CPA (through canSend and canRecv) elements acts somewhat like a SOAP WSDL, and the XSDs serve the same purpose as with SOAP, so it's not too far off.

There does exist software for turning types defined in XSDs into messages (merging in user-supplied data) at runtime, but per my question there's no obvious tooling for code generation around CPAs and related XSDs.

Furthermore, actually writing software to do this yourself is made more problematic by the dificulty of searching for the meta-grammar for XML Schema (i.e: that grammar which remains of XML Schema once XML tokenization is factored out). Basically, this was difficult because in the XML world, the word "grammar" has an different meaning which polutes search results.

I was able to write a parser for the XML syntax snippets present at the top of each of the MSDN articals on XML Schema (elements listed down the left), which in turn allowed me to generate an LL1 grammar for XML schema which works on the pre-parsed AST of a given XSD.

From there I built a top-down parser from this meta-grammar which:

1. Follows <xsd:import>s and <xsd:include>s to resolve namespaces into further XSDs.
2. Recursively resolves message types in order to produce a 'flattened' type for each CPA message.
3. Generates a packer/unpacker data-structures for the message types which allow generation of code in various languages, as well as serialisation to and parsing from validated 'payload' XML.

There are still various XML Schema restrictions, keys, and other constraints that my code generators don't know about, but support for these can be added in time.

I'll update this answer with links to grammars (and possibly code -- depends on legals) as time permits. I'll leave the question as non-accepted for a while so that if someone miraculously finds a tool which makes much less work of the code generation, I'll accept an answer based on that.