Oracle7, EDI, and APIs

I'm working on the opening phase of a semi-public brokerage system of a sort. It wants to work like this:

  [buyers] <--x.25 service--> [Oracle7 server]

Central server runs Oracle7. It has a set of records for, say, "baseball cards". Several large firms, clients, are interested in buying certain cards as they become available.

For the buyers, I need to specify an API for how they can connect their _Existing Systems_ to my server. They already have in-house systems (IBM, DEC, etc.) for tracking their existing baseball card collections. Each buyer will have his own strategy for buying cards, and I want to be able to allow somewhat sophisticated queries with minimal dumping of unwanted data -- no big streams of raw info!

I've toyed so far with two ideas:

1. Make everybody get and use SQL*Net. We then run TCP/IP over x.25. Implement the API as one or more Oracle7 stored procedures.
2. Make everybody write custom programs for low level RPC, using x.25 or Berkeley sockets or the like.

My questions are these:

1. What other good approaches are there? Is there an EDI standard for this?
2. What are the trade offs between options 1 and 2, other than the price of SQL*Net?

Many thanks in advance.

 -Tom

-- 
Thomas Cox      DoD #1776   '91 CB 750 Nighthawk   tcox_at_qiclab.scn.rain.com
    The Platinum Rule:  "Do Unto Others As They Want To Be Done Unto"