2011-06-28

a brief history of compound documents

5.7: web.adde/compound doc/problems:
. the compound doc is a really simple idea;
it works just like the way that your mac's gui
displays a window of various apps,
except that window arrangments can be
saved as documents, and windows can be borderless
as if they are part of the same document .
. but from reading opendoc's history
you'd think it was a plague .
"(. compound documents are said to be
an oversold concept:
there just aren't that many examples
beyond mixing graphics with text .)
--
. tell that to the html`object tag:
we routinely see combinations of
movies, photo's, text, script images,
and anything you have an app for .
. an amazingly bad specification or implementation
was opendoc's biggest problem:
it was very common to find
apps that could not even
open a document created by another app .
. OpenDoc attempted to solve this problem by
allowing developers to store multiple formats
to represent the same document object.
For instance, it was both possible and encouraged
to store a common format like JPEG
along with an editable binary format,
but in practice few developers
followed this recommendation.
--
. something about the plague again:
other compound doc specifications
had the same problem!
. the specification should have included
a manifest that listed what app's you need
in order to open a given document .

more compound doc' technology is history:
Dynamic Data Exchange (DDE, 1987),
allowed "conversations" between applications.
OLE(1991, (Object Linking and Embedding).)
was Microsoft's first object-based framework,
and MS`Office's first compound doc' technology;
it was built on top of DDE .
. While OLE 1 was focused on compound documents,
COM and OLE 2 (1992-93) were designed to address
software components (oop++) in general.
. OLE custom controls (OCXs, 1994)
. Internet is a new use for
OLE Custom Controls (ActiveX, 1996),
-- gradually renamed all OLE technologies to ActiveX,
except the compound document technology
that was used in Microsoft Office.
DCOM (Distributed COM, 1996)
competed with CORBA as the model for
code and service-reuse over the Internet.
difficulties getting either of these
over Internet firewalls .
MTS run-time increased scalability, robustness,
and simplified system management.
. ms`COM is often an umbrella term for
OLE, OLE Automation, ActiveX, COM+ and DCOM .

[ com is oop++ ]
COM's architect"Anthony Williams:
Object Architecture
is concerned with Dealing With the Unknown
and ensuring Type Safety in a
Dynamically Extensible Class Library;
also significant to com
was clarifying what oop`Inheritance is,
and knowing How To Use It .
Charlie Kindel 1997:
(popular) oop =
Polymorphism + (Some) Late Binding
+ (Some) Encapsulation
+ Inheritance

Component Oriented Programming (cop) =
Polymorphism + (Really) Late Binding
+ (Real, Enforced) Encapsulation
+ Interface Inheritance
+ Binary Reuse” .
C++ supports only oop not cop
so, COM must additionally specify:
* Execution environment options
(so-called Apartments)
* Inter-process Marshalling
* Remote Object Activation mechanism and protocols
* Threading models
. the C++ linkage model impedes
binary distribution and reuse .
. by using shared object linking,
the lack of binary standardisation
means there is an interoperability problem .
C++ lacks binary encapsulation:
ie, while it supports separation of
interface and implementation,
it's only at the syntax level
– not at the binary level.
implementation changes are “seen” by clients.
com provides what c++ is missing:
A “substrate” for building re-usable components.
. Interfaces are defined in COM IDL
(IDL + COM extensions for inheritance and polymorphism)
OS Neutral and (nearly) Language neutral:
. can be used from any language that can
generate/grok vtbl’s and vptrs.
. a packed bit field is returned
with every COM access .
categories define
an implementation of a given interface
that meets some set of constraints .