Related Items in a Catalog

[Transpyre]

I am building a product catalog systme using PHP and MySQL and the client would like to have related items also displayed when an item is viewed. The items have a category and sub-category listing, and I considered just pulling a random item from a shared sub-category, but that doesn't seem that it would be very useful.

Any thoughts on good ways to handle this?

[rabbitdog]

I've handled it two ways in the past:

a. allow the client to explicitly set related item groups.

b. allow client to specify keywords for items, then build relationships based on matching keywords.