I don't know is the definition WSDL not enough?

Section 3.2.2 of the jBPM BPEL user guide explains that processes are defined in terms of abstract WSDL definitions (e.g. messages and port types) and XML schema types/elements only. That's the information that goes to the database.
Nevertheless, the information provided at the abstract level is not enough for a client to interact with the service. You still need protocol-specific details (for example, SOAP actions, namespaces, etc.), referred to as bindings, and actual endpoint access information, provided by ports.

This is comparable to the clean interface exposed by a session bean against which you program the web tier, as opposed to the deployment descriptors that specify how and where you access an instance of it.

is the web archive not enough to allow outside accessable

Yes, it is. The user guide, sect. 3.2.5 explains that the implementation WSDL definition provides enough detail for a client program to be implemented in any platform. Yet we package and deploy an application client JAR on the server so that our test client invokes the service through a strongly-typed dynamic proxy.