Interface Points in Web Objects

The CCI and CGI interfaces point to a general need for interprocedure comminication between web applications and other applications. Here are some critical interface points between components of the web.

GET: Serialization/Externalization/Pickle

The GET operation in the web retrieves the persistent state for an object across the network, so that the object can be activated/initialized on the client side.

Typically, the persistant state of an object is stored in a file, i.e. a document on the desktop. But it can also be in a database, or the output of a computation.

Activate from Remote Persistant State
System Facility Example
libwww HTAccess, SGML parsing request = ...;
HTRequest_setOutputStream(request, output);
HTAnchor * anchor = HTAnchor_findAddress(url);
HTRequest_setAnchor(request, anchor);
return lauch_request(request, NO);
... parse stream, call SGML_start(), SGML_data(), SGML_end()...
COM Monikers, persistance um = URLMoniker("http:...")
ctx = CreateBindingContext()
str = um.bindToStream(ctx)
CoCreateInstance(read_uuid(str), &obj, IID_Document))
M3 network objects Stable, pickles. lm = NEW(WebLogManager.T).init(); (* WebLogManager.T <: LogManager.T *)
obj = NEW(Document).init("http://...", r, lm := lm);
.. which calls: lm.recover("http://...", log, checkpt)
.. obj.readCheckPoint(checkpt)
... Pickle.Read(checkpoint)
... obj.replayLog(log)
Java URLConnection, Serialization
CORBA persistance, Externalization pid = PIDFactory.create_from_key("http://...")
/* CosPersistancePO::PO.restore */ /* hmmm... no way to access the persistant data directly!!! */

Note that web objects are animated by a variety of software systems on a variety of platforms. HTML works well across systems.

Tricky issue: type fingerprints (a checksum of the type definition). Modula-3, Java, ILU, and probably other use them, but they are specific to the type system. Hence, a persistance format like M3 Pickles or Java Serialization is unsuitable in the common case.

Format Negotiation is negotiation about the persistance format. Note that the APIs of the systems other than the web assume a single persistance format, and lack the equivalent of "accept" headers in their binding parameters.

Format negotiation should not be used for more ambitious purposes like different documents for different screen sizes, user agent capabilities, etc. Or should it? How does PEP relate? Perhaps interface negotiation can be combined with format negotiation; perhaps a contract is a contract is a contract, whether it's about the persistance format, client capabilities, commercial agreements, etc.

Type fingerprints map nicely into URL schemes: m3fingerprint:xxxx, java:xxxx, ilu:xxxx, and they are analagous to DTD system identifiers ala <!doctype html system "http://...">

XML should work well in this capacity as well. Hence an XML parser/generator API should support "marshalling" ala M3 StableGen logs, Java Serialization, CORBA externalization, COM serialization.

See also: an essay on pickling ideas.

Hmmm... both M3 and CORBA have a way of connecting an object to a store such that the store tracks updates to the object (stable.init() and PO.connect, resp.). See also: compound document architectures for update-in-place file formats like Bento and Structured Storage.

@@@@ M3 sources

CORBA persistance, 5.4: OIDs are for sharing, PIDs are not. pom_id: name of POM is passed around at runtime? (analog of clsid?) pre_store/post_store: concurrency?


Invocation, Interface/Implementation Repository

System register class implementation create instance generic call
Web servers /cgi-bin, config files opaque POST, www-form-urlencoded
Java class loader new apply in reflection API
CORBA registration of implementations BOA::create. Called by implementation. Must provide all interfaces at once. CORBA DII
COM CoRegisterClass CoCreateInstance, called by client, who asks for any one interface. IDispatch::invoke

(for example see visual Tcl)

ILU ilu_Publish() called by impl (I think) ???
  _ILU_C_GenericCall (ilu_Class class, ilu_Method method,
                      _ILU_C_ExceptionDescription evec,
                      ILU_C_Object *discriminant,
                      ILU_C_ENVIRONMENT *status,
                      char *argdesc, ...);

Novel ideas in invocation:

python class object
perl objects (i.e. blessed references)
closures. "mortal" stuff.
smalltalk objects
multiple inheritance. Blocks (i.e. closures?)
(generic functions)
prototype-based object system
OSA, Open Scripting Architecture from Apple.


Generalized Information Systems

Stanford Digital Library Project
and data warehousing project Done with ILU

Relational Database

@@ need to review CORBA query service, etc.

Microsoft's relational database API. Anybody got any pointers to the actual technical spec online? What's ODA? Is this an OO API at all? Any relationship to COM?
Berkeley-DB routines.
Perl DBI


@@ review of CORBA security spec ongoing.

Clifford Neuman Something of an expert in security and distributed systems. See his papers, including Proxy Based Authorization and Accounting for Distributed Systems
Capabilities. e.g. Python Crypto Toolkit
CORBA licensing, COM licensing
logging, notification. resource limits: Penguin

Name Service

See Also: Addressing: URIs, URLs, etc.


Modula-3 Thread Interface

User Interface

Mac Toolbox
MS Windows API

Updates to CCI and CGI

CCI @@need link
IPC mechanism to control NCSA Mosaic. Also: netscape client API, Spyglass SDI
CGI. Should be replaced by something in this arena. Also, Netscape server API, Process/Microsoft's ISAPI (need links@@).
see: fcgi in ISL
Netscape Plug-ins
@@need to review
ActiveX controls
same as OLE controls? Which COM interfaces? What non-com interfaces are used by existing OLE controls? e.g. to open files, draw on the screen...

Netscape plug-ins have been grandfathered. (i.e. there's a control that runs plugins)

OpenDoc Parts
specified using CORBA. (where are the interfaces?). Again, plugins have been grandfathered.


Compund Doucment Architecture: OLE, OpenDoc, Fresco, ...
HTTP-NG using ILU? ala Object Interchange Service from Stanford Digital Library Testbed
Next Generation CGI technologies
client integration: helper apps, CCI, DDE, OpenDoc, ActiveX
The Web Object Model and Type System

$Id: Overview.html,v 1.11 1999/05/17 14:45:29 connolly Exp $