OO solution?

In keeping with other discussions in cdt, I can't help but wonder if it
wouldn't be cleaner to use an OO solution. Just create a Document
class, and an abstract Viewer class extended by a Group class and a
User class. Each Document object can maintain a list of Viewers which
can view it. Each Viewer object can maintain a list of Documents which
it can view; each Group object can store a list of users that are a
part of it; applicable monadic properties for User objects is left as
an exercise.

I'll bet the application code would all but write itself. Plus, you
can encapsulate these properties and then expose Document methods of
canView(Viewer v) or Viewer methods of makeDocumentViewable(Document
d)... the cool thing is you can carefully change the underlying
implementation of such methods without breaking any code that calls
them.

Did I miss any other benefits of utilizing the OO paradigm? Are there
any cons?

sreedhardasi@xxxxxxxxx wrote:
I have a database design questions. How can we specify one of two
columns in a table should be not null? In other words, if one column is

null then another column should not be null. Here is an example. Let's
say we have document and we need to specify permissions to the
document. The document has either individual or group level
permissions.

Document table
doc_id int primary,
doc_name varchar(50) not null


User table
user_id varchar(50) primary,
user_name varchar(100) not null


Group table
group_id int primary,
group_name varchar(50) not null


UserGroup table
user_group_id int primary,
group_id int not null,
user_id varchar(50) not null


DocumentPermission table
doc_id int,
group_id int,
user_id varchar(50)


So, either group_id or user_id should not be null in the
DocumentPermission table. Is there anyway we can have constraint like
this on the table? Is creating another group for that user the only
solution (Involves more administration)? Any help would be appreciated.



Thanks,
Sreedhar

.