Re: Syntax and semantics. WAS: RE: Init is dead?

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