[ontolog-forum] UML and Semantics

["David C. Hay" <dch@xxxxxxxxxxxxxxxxxxxxxxx>]

At  12/2/2012 11:57 PM, John Sowa wrote:
> KI
> > entity relationship model semantics can exist in self-describing
> structured data.
>
> Yes.  E-R diagrams were introduced in 1976.  Even earlier,
> there were
> Bachman diagrams, type hierarchies, and Petri nets.  Versions of
> all
> those diagrams were combined in UML, 

No.  UML was developed specifically to support object-oriented
program design, and had only minimal relationship to the earlier E/R
notations.

> and mainstream
> programmers used
> them to specify programs and databases. They developed tools to draw
> the diagrams and map them to and from the software.
>
> Just two kinds of UML diagrams provide 99% of the useful subset of
> OWL:
> type hierarchies and E-R diagrams.  Controlled English could be
> added
> as a very readable supplement or extension.  If the SW had adopted
> that
> as the official strategy, mainstream IT would have a smooth
> migration
> path to ontology-based tools.
I realize that "UML" has captured the imaginations
of a lot of data modelers.  The problem is that the UML class
diagram, as originally designed, doesn't address semantics at all. 
It is not a "useful subset of OWL type hierarchies and E-R
diagrams".  It is something quite different. 

In the OO world it came from, a "class" simply refers to a
piece of program code that describes something to be manipulated by the
computer.  Only accidentally might a class refer to a collection of
things in the world.  As a consequence, there are several important
implications:

1. There are no constraints as to what constitutes a
"class".  It might be a class of things in the world
("person", "project", etc.), or a class of things to
be manipulated by the computer ("screen",
"interface", etc.)  In semantic modeling, we are concerned
only with classes of things of significance to an organization. John
previously wrote a compelling essay on the conflict between calling these
"entity classes" or "entity types", but I don't want
to go into that here.  The point is, they are not OO
classes.

2. There are all kinds of bits of notation that apply only to the
programming world.  ("visibility", etc.)

3. (And this is most important), an "association" is not
about structure.  In the E/R world, a
Relationship is about two (entity) classes.  It represents the
structure of something in the world, as expressed in a sentence of the
form: <subject entity class> <predicate> <object entity
class>.  Thus, a relationship name represents a predicate in a
semantic assertion.   In UML, an association is a
navigation path for software to transverse.  This
means that  a "role name" is not a predicate at all. 
It is simply a label for the 2d class.  (You see, even though both
an attribute and an association are "properties" of the first
class, the 2d class at the other end of the association is not permitted
to be part of that property.  (It's about something called a
"namespace".  Don't ask.))

I spent some time hanging out with the Object Management Group people and
was inundated with the propaganda that "Oh, thanks to
"stereotypes", you can get UML to cover anything". 
It took a long time for me to get my head around point 3, above, but
finally decided to address the problem. 

So, in my latest patterns book, Enterprise Model Patterns: Describing
the World, I decided to use UML instead of my favorite
notation.  By addressing the premises I just mentioned, it turns out
I could use a modified form of the UML class notation to create semantic
models.  

(Among other things, I had to add the Barker/Ellis standard for naming
relationships to incorporate semantics.  Thus, UML
"roleNames" became E-R predicates.)  

It worked!  I would submit that that book is a candidate for a
"high-level" ontology. 

Because I had now convinced my E/R buddies that I had "gone over to
the dark side" by using UML--as well as annoying my UML buddies for
having completely bastardized their notation--I wrote a companion, UML
and Data Modeling: A Reconciliation.  This book specifically
addresses the issues of trying to describe semantics with a notation that
was not originally designed for it. 

I welcome any comments and responses. 

Dave Hay

_________________________________________________________________
Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/  
Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/  
Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx
Shared Files: http://ontolog.cim3.net/file/
Community Wiki: http://ontolog.cim3.net/wiki/ 
To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J    (01)