We have an e-commerce shopping site with over 8000 products and over 100 categories.
Some sub categories belong to multiple categories - for example, A Christmas trees can be under "Gardening > Plants > Trees" and under "Gifts > Holidays > Christmas > Trees"
The product itself (example: Scandinavian Xmas Tree) can naturally belong to both these categories as well.
Naturally these two (or more) categories have different breadcrumbs, different navigation bars, etc. From an SEO point of view, to avoid duplicate content issues, I see the following options:
Use the same URL and change the content of the page (breadcrumbs and menus) based on the referral path. Kind of cloaking.
Use the same URL and display only one "main" version of breadcrumbs and menus. Possibly add the other "not main" categories as links to the category / product page.
Use a different URL based on where we came from and do nothing (will create essentially the same content on different urls except breadcrumbs and menus - there's a possibiliy to change the category text and page title as well)
Use a different URL based on where we came from with different menus and breadcrumbs and use rel=canonical that points to the "main" category / product pages
This is a very interesting issue and I would love to hear what you guys think as we are finalizing plans for a new website and would like to get the most out of it.
moopy - What you're describing is called "faceted" navigation, and we've had a number of recent discussions about it which take an approach that I think get it right.
Unfortunately, the best discussions start out approaching the topic from a different mindset, using different vocabulary to describe the situation, so you might have a hard time finding them.
This recent discussion, IMO, is the best of the bunch, summing up much of what came before and linking back to the most relevant preceding discussions. It's called "Should I flatten my store's URL structure for better SEO?"... and probably should be called... "Best Approaches to Implement Faceted Navigation"....
IMO, this approach using just one url for the product page (and linking from different category and subcategory pages) is the least likely to create problems.
Note that the thread refers back to earlier threads which discuss breadcrumbs, etc.
To avoid multiple live discussions on the same topic in the forum here, I recommend expanding on any thoughts anyone might have about your hypothetical approaches in this thread... but continuing discussion of particulars of the early February 6th - 13th approach in that thread, still active and noted above.