- From: Mark Hinnebusch <mark.hinnebusch@infotechfl.com>
- Date: Mon, 15 Jan 2001 16:40:20 -0500
- To: Sebastian Hammer <quinn@indexdata.dk>, "LeVan,Ralph" <levan@oclc.org>, "'ZIG'" <www-zig@w3.org>
Sounds like a better approach to me. -mark h At 10:05 PM 1/15/01 +0100, Sebastian Hammer wrote: >At 14:38 15-01-01 -0500, LeVan,Ralph wrote: > >[Ralph moves the discussion to include the encoding issue so I will follow >suit] > >>All implemented standards have three component: A semantic, a syntax and a >>content rule. The combination of the first two is usually called a >>protocol. (Actually, I guess there is a fourth component, the transfer >>mechanism, which is raw TCP/IP for us.) In the case of z39.50, we've been >>locked into a single syntax (BER) and have gotten away with calling z39.50 a >>protocol. > >Is that paragraph meant to suggest that you feel most protocols are NOT >locked into a single syntax? I think that would actually be pretty >unusual. Running an OSI stack would, in principle at least, allow you to >negotiate other encodings than BER (including, presumably, XER). TCP/IP >doesn't directly support that kind of negotiation, and as a result, I >believe that the vast majority of Internet protocols are pretty rigid in >terms of their syntax. > >I agree completely that by dropping the init or changing the syntax, we >are in fact creating a new protocol - the first and most noticeable effect >of which will be that interoperability with old implementations becomes >more complex. > >We will need to think carefully about how we talk about these things. At >present, the Z39.50 protocol gives you relatively straightforward >interoperability with anything deployed since 1992 (thanks partly to the >Init service I might add). A new "Z39.50 protocol" throws that to the >wind, gateways or no gateways. Three new "Z39.50 protocols" do it thrice >over. How do we avoid chaos when Z39.50 ceases to imply syntactic >interoperability. > >I think at the meeting, Ralph, you hinted that perhaps new syntaxes >(protocols) should be seen as parallels to new APIs - just other ways of >representing the same thing for different purposes. Perhaps it should be >seen as a parallel to CORBA, which, I believe, allows different language >mappings and even different protocols - but it suggests only one protocol >for cross-broker interoperability - the IIOP. > >Maybe (just maybe) it makes sense to keep crusty old Z39.50 over BER as >our internet interoperability protocol. After all, it works, and we're not >alone - LDAP, SNMP and SSL use it to good effect. > >Dropping the Init I see as a less challenging issue. It's not hard to make >optional for most client OR server developers, and it would be a pretty >simple switch to set in your client setup. Most old-style servers would >probably also fail fairly gracefully (by dumping the connection) if they >were confronted with an un-initialising client. > >--Sebastian >-- >Sebastian Hammer <quinn@indexdata.dk> Index Data ApS >Ph.: +45 3341 0100 <http://www.indexdata.dk> Fax: +45 3341 0101
Received on Monday, 15 January 2001 16:37:52 UTC