You're saying that columns can have an is-a relationship with abstract types. That's equivalent, in my mind, to saying that the attributes of an instance have an is-a relationship with the native datatypes of the language I'm working in.

IS-A and HAS-A are more often discussed in reference to the object, not the attributes. That would, in my mind, correspond to the row in the table or the table definition itself. So, tables don't have IS-A relationships. Rows in tables don't have IS-A relationships. A given row in a table has a HAS-A relationship with every row that it is the N side of a 1:N relationship. (The confusion might be arising in that OO theory gives the container the HAS-A control while DB theory gives the contained the HAS-A control.)

That said, you can approximate an IS-A relationship between tables, but it's cumbersome and prone to mistakes. (It's kinda like doing OO in AppleBASIC or Fortran.)

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.