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Dear all:

I just found out that some sites use the <base> element in shop pages for defining the base URI for relative references (e.g. "#offer").

Be careful when using <base> in combination with RDFa, because you may spoil the identifiers of your data objects:

For instance, 

   <base href="http://www.myshop.com/info" />

means that 

<a href="/payment/">Payment Options</a>

will link to 

    http://www.myshop.com/info/payment

This is often the intended effect.

Unfortunately, it will also mean that an RDFa element with a relative identifier, e.g.

<div typeof="gr:Offering" about="#offer">
...

will get the global URI

   http://www.myshop.com/info#offer

Now, since you usually have many different offers they will all get the same URI, which renders your data useless.

So if you want to use <base> with RDFa, then you must choose one of the following approaches:

1. Take the true ("canonical") URI of the individual page as the base URI, e.g.

    <base href="http://www.myshop.com/products/camera1234" />

OR

2. Use full URIs for all "about" properties, e.g.

    <div typeof="gr:Offering" about="http://www.myshop.com/products/camera1234#offer">

If you send the "deep" URI of the actual page to the template engine as a parameter anyway, you could also write

    <div typeof="gr:Offering" about="{{pageURI}}#offer">

or similar. The exact syntax will depend on your templating engine, of course.

Best wishes

Martin Hepp

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[goodrelations] <base> and relative URIs