Entity Relationship Modelling

I started filling out Excel worksheets with column names for a DB I'm creating for my DMT class. Each worksheet represented a table in my DB. I realised that my brain would soon explode unless I had some way of plotting how the tables related to eachother. I searched the web and found two gems...

The first is a library of exisiting database schemas for common systems <http://www.databaseanswers.org/data_models>. These are handy blueprints to have and I recommend that my fellow DMTers browse through it (unfortunately, it didn't have anything that quite fit what I'm building). What I got out of it was being reminded of the notation that's used in Entity Relationship models (I was also reminded of the term "Entity Relationships"!).

originally proposed by Peter in 1976 [Chen76] as a way to unify the network and relational database views. Simply stated the ER model is a conceptual data model that views the real world as entities and relationships.

(http://www.utexas.edu/its/windows/database/datamodeling/dm/erintro.html viewed 14th May, 2007)

The part I love most about ER modelling is the notation used. Once you learn it, it makes you feel smart - and it's so easy. Any time-poor sod can learn it within a few minutes. "Crows feet" and "one-to-many" relationships etc. the following diagram sums it up really well. Can't wait to add it to my System Plan, I almost feel like a real IT geek.

Click here for full-size image.

XHTML Not Fully Supported by IE?

While researching for my DMT "Micro and Macro Analysis", I came across a web page that surprised me. It seemed to say that XHTML is not fully supported by IE (should I be surprised?). The page can be found at <http://www.w3.org/2000/07/8378/xhtml/media-types/results>.

I included this 'IE' fact in my "Analysis" but it seemed like a bit of a lazy blanket statement so I revisited the above web page tonight - to try and make sense of what the test results actually mean. I am having trouble understanding what it does means and would love if someone could throw a layman's explanation my way.

Basically, what is the difference between the four scenarios being tested?:
1. text/html
2. application/xhtml+xml
3. text/xml
4. application/xml

And how do these different 'types'(?) exist in an XHTML document? What would the declarations for each look like? I looked at sample code for 1. and 2. and can't actually see any difference!?

Example for 1. <http://www.w3.org/2000/07/8378/xhtml/media-types/test.html>
Example for 2. <http://www.w3.org/2000/07/8378/xhtml/media-types/test.xhtml>