How to build database to support user-specified attributes?

A few constraints:
1. Any attributes defined is "private" to the defining club. Other clubs aren't aware of it although they may define custom attributes of their own with the same name and type. [Perhaps there is a way to share definitions of identical attributes?]
2. A club doesn't have to define any custom attributes.

Has anyone done anything similar?. Any ideas on how it might be done?

Kunle

• BEGIN DDL =================== CREATE TABLE FootballClub ( Club_ID int IDENTITY, Name char(80) NOT NULL, Area char(4) NOT NULL, League char(4) NOT NULL, City char(30) NOT NULL, PRIMARY KEY (Club_ID)
  )
  go

exec sp_primarykey FootballClub,

       Club_ID
go

CREATE TABLE Player (

       Player_ID            int IDENTITY,
       First_Name           char(30) NOT NULL,
       Initials             char(30) NULL,
       Last_Name            char(30) NOT NULL,
       Date_Of_Birth        datetime NOT NULL,
       Position             char(4) NULL,
       Club_ID              int NULL,
       PRIMARY KEY (Player_ID),
       FOREIGN KEY (Club_ID)
                             REFERENCES FootballClub

exec sp_primarykey Player,

       Player_ID
go

CREATE TABLE UserAccount (

       User_ID              int IDENTITY,
       Club_ID              int NOT NULL,
       FullName             char(80) NOT NULL,
       Logon                char(20) NOT NULL,
       PWD_Hash             char(60) NOT NULL,
       PRIMARY KEY (User_ID, Club_ID),
       FOREIGN KEY (Club_ID)
                             REFERENCES FootballClub

exec sp_primarykey UserAccount,

       User_ID,
       Club_ID

exec sp_foreignkey Player, FootballClub,

       Club_ID
go

exec sp_foreignkey UserAccount, FootballClub,

       Club_ID
go

=================== END DDL ===================