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                   *          DB/C Newsletter          *
                   *            April 1995             *
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                             Editor's Notes

     The topic for this month's newsletter is OLE and OpenDoc.  There are many
misconceptions about what OLE and OpenDoc are useful for.  In my opinion, OLE
and OpenDoc are not particularly useful in creating the types of applications
that are typically created with DB/C.  (There is a good probability that I am
wrong about this - if you can find a use, let me know.)  More interesting to
me are the underlying software layers called COM and SOM.  I am not an expert
on any of these emerging technologies, but hopefully this article will provide
you with some insight into what these creatures are about.

                                                           don.wills@swc.com

                        OLE, OpenDoc, COM and SOM

     Here is a quick summary of the acronyms in the title:

OLE stands for Object Linking and Embedding.  OLE is Microsoft software that
is available only on the various Windows operating systems.  OLE is available
for Windows 3.1 and Windows NT 3.5.

OpenDoc is an Apple/IBM software standard.  Apple has shipped a beta test
version of OpenDoc for Mac OS 7.5.  IBM has announced plans to release OpenDoc
for OS/2 and AIX.

COM stands for Component Object Model.  COM is a Microsoft software layer that
defines a programming language independent interface for object-oriented
programs.  It is the layer that underlies OLE.

SOM stands for System Object Model.  SOM is an IBM-defined, non-proprietary
programming language interface that is similar to COM.  It is the layer that
underlies OpenDoc.  SOM and DSOM (Distributed System Object Model) are
available for AIX and OS/2.  SOM is also available with the beta test version
of OpenDoc for Mac OS 7.5.

     The basic concept behind both OLE and OpenDoc is the document.  OLE and
OpenDoc are described as document-centric, not application-centric.  Both are
meant to allow component software to fit together in a coherent fashion such
that an end user can operate on a single document using different applications
(component software) on different parts of the document.  A typical example is
a newsletter that contains text and graphics.  Instead of purchasing a single
application that does both text and graphics, one can purchase a text component
and a drawing component separately, but have them work on the same document in
the same window, sharing menus and functions (like Open, Save As, etc.).  This
allows the end user much more flexibility in choosing the software that is
most appropriate for his needs.

     Programming for such an environment is quite complicated.  The number of
interactions between components is quite large.  What if vendor A wants to
write their component in C++ and vendor B wants to write their component in
Smalltalk?  The need for a language independent API is apparent.  But does the
the API have to be object-oriented?  Why can't it be just like other APIs for
operating systems?  The answer is that object-oriented programming makes
complicated programming interfaces easier to use.  The extensibility of an API
in an object-oriented environment is far superior to a traditional API.  The
complexity of OLE and OpenDoc are what caused the need for COM and SOM.

     Let's look at some of the specific concepts of OLE and OpenDoc.  OLE and
OpenDoc Software comes in two forms:  'container' software and 'part' software.
In the newsletter example, word processing software is the 'container'
software and the drawing program is the 'part' software.  If a spreadsheet was
also embedded in the newsletter, spreadsheet software would also be 'part'
software.  It is possible for application software to be the 'container'
software for one document and 'part' software for another document.

     The 'container' software is the controlling software.  It is the software
that controls the menu and dispatches messages to the 'part' software.  Many
user actions cause messages to be dispatched to one or all parts.  For example,
when the user selects the File Save menu option, a message is sent to all of
the 'part' components in the document so that each can do the save operation.
When the user clicks on an area of the document controlled by a 'part', then
the menu is changed to reflect the valid menu options available for the
respective part.  For example, when a graphic area is selected, such draw menu
entries as Color and Line Width are installed in the menu.  All possible
interactions between 'containers' and 'parts' are defined by OLE and OpenDoc.

     Both Microsoft and Apple/IBM have tried show that their respective
technology is superior.  In reality there are more similarities than there
are differences.  One notable difference is the fact that a 'part' area of
an OLE document must be rectangular, whereas in OpenDoc it can be any
irregular shape (think about flowing text around a round picture).

     Microsoft, Apple and IBM have all made large commitments to their
respective technologies.  It is unclear whether one technology will prevail
over the other, or whether both will succeed.  It is even possible that both
will be somewhat unsuccessful - because not all problems fit into the document
model.  Remember the old saying - if all you've got is a hammer, everything
starts to look like a nail.  Not everything is a document.  Time will tell.


                            DB/C Class Schedule

     The next DB/C class is scheduled for April 10-13, 1995.  The class is
held in the Oak Brook, Illinois office of Subject, Wills and Company.  For
more information, contact Judi Tamkevic via email at dbc@swc.com or via
telephone at (708) 572-0240.