1. what - an absolute joke

   1. consider rpc; consider differing host architectures

   2. consider presentation protocols - xdr, ascii text

   3. consider xml

2. but first, consider sgml

   1. sgml - standard (or simple) generalized (or generic) mark-up language

   2. standard - iso 8879

   3. generalized - applicable to a wide range of information; the dtd

   4. mark-up - describe structure, not content or presentation

   5. language - generators, checkers, parsesr

   6. html is the best-known instance of sgml (sorta)

3. now consider xml

   1. sgml is complicated - description, macros, parsing can be hard

   2. enter xml - simpler, less general, "the parts of sgml that microsoft understood."

   3. dtds are still around; it's still text-based; tags are less unruly; less emphasis on representation issues

   4. there are many aligned protocols - style, linking, and so on

   5. xhtml, mathml defined using xml

4. on to xml-rpc

   1. xml-rpc is the result of confusing transport and presentation protocols

   2. nominally, xdr is "no good", although why isn't made clear

   3. xml is much better - oh, and by the way, use http as the transport

   4. people who can't comprehend xdr certainly won't be able to use it with http

      1. hint - use the post method

   5. xml-rpc components

      1. identifies supported types - int, bool, string, blob, structs; no user-defined data structures

      2. request-response structure - posts mostly

         POST /RPC2 HTTP/1.0
         User-Agent: Frontier/5.1.2 (WinNT)
         Host: betty.userland.com
         Content-Type: text/xml
         Content-length: 181
         

      3. xml call-response structures

         1. <methodCall>
              <methodName>examples.getStateName</methodName>
              <params>
                <param>
                  <value><i4>41</i4></value>
                </param>
              </params>
            </methodCall>
            

         2. <methodResponse>
              <params>
                <param>
                  <value><string>South Dakota</string></value>
                </param>
              </params>
            </methodResponse>
            

   6. it is unclear of procedure-call naming conventions are defined anywhere

   7. asynchronous extensions to the rpc model - call and continue; multi-calls

5. simple object access protocol - like xml-rpc, but more

   1. defines an envelope document to containing requests and responses

   2. defines extensions to the xml-rpc model

6. those who don't know the past are doomed to repeat it, usually as farce

This page last modified on 3 May 2001.