Take a different route. It's called reverse engineering:
- Study the functionality of this site.
- Collect all the use cases.
- Work out the system requirements by analyzing the use cases.
- From the system requirements create a list of data collections.
- From the system requirements create a list of all function points.
- Work out the relations of the data collections by anaylzing how the function points interact with the data collections.
A little hint: A function that has a part (or all) of one data collection as an input and returns a part (or all) of another data collection as it's result implies a relation of data collection 1 to data collection 2. A function with a data collection and returning one or more entities might be a filter etc. pp.
Regards,
-MRB