Object Oriented Design Confusion

[JPL]

Hello,

I hope you can help me. I am running PHP5 on Windows. I am new to PHP and object-oriented design.

I am creating an web-application that will allow users to upload images to a database. I would like each user to have his/her own user name and password. Additionally, I would like to be able to set up groups of users, which might have different permissions to view different files/folders.

Furthermore, I would like to be able to keep track of the actual person who took the photograph, which I will call a Contributor. A contributor might give his photos to an existing user (say on a CD) in order to upload, or a user might be a contributor themselves, in which case they would log in and upload their own photos.

So that is the scenario. I am having trouble designing the classes for this system.

My thinking so far is this:

1) Have a class of Member. This class will hold information like what permissions the member has.

2) Have a class of User which extends Member. Additional properties will include username and password.

3) Have a class of UserGroup which also extends Member. Additional properties will include a list of Users that belong to this group.

My first question is this: is the above good OO design? If not, why not?

Moving on...

I also need a Contributor class. This class will hold info about a contributor - like his name, contact details and his web-site address.

But sometimes users can also be contributors. However the User class can't extend more than once (it already extends Member). How do I deal with this situation?

Or maybe I'm going about this completely wrong??

Please help...

[glcarlstrom]

For what it's worth:

First, from a logical perspective, I don't know how much sense it makes to extend Member into UserGroup. A UserGroup doesn't seem to need much of Member's functionality (permissions, etc.); it's just a high-level grouping of User objects. Essentially it's a wrapper class around an array of Users. I would make UserGroup a stand-alone class, not extending anything.

As for the Contributor/User/Member problem, I would get rid of the Member class entirely; it seems superfluous. How about making Contributor your top-level class? The Contributor class can define basic functionality and properties that are present in Contributors and Users (name, etc.). Then make User an extension of Contributor.

Think of OO design/inheritance like those elementary school logic problems. If all Users are (or at least can be) Contributors, but not all Contributors are Users, then User should be an extension of Contributor. Make sense?

This way we trim some of the fat (Member) and simplify the OO logic a bit.

Hope this helps.