When thinking about "Open Data" (possibly due to nothing more than my own ignorance) I am utterly confused as to what difference an open licence legally makes for structured data.
"Open Data" for me is a bit like saying "Free Air".
From discussions with other (fairly knowledgeable) people on the matter (for example, this nice summary), it seems I'm not alone in my confusion. Before I ask the concrete question (which will be: "why should I care how a structured dataset is licenced?") I feel I need to cover my own potentially flawed understanding of the matter (so sorry in advance for the long question).
So let's say we have a dataset—let's say the IMDb dump. I am very interested to use the IMDb dump. The IMDb dump is publicly available for download from the Web. Great! ... but it doesn't have an open licence. Hmm.
But wait ... what legalities actually stop me from exploiting the factual content of the IMDb dump regardless of licencing or what the providers of the dump have to say?
As far as I can tell, legally speaking, assuming the dataset is comprised of factual content and that it's the factual content I am interested in using (e.g., the movie Dune was 137 minutes long) the only thing I have to avoid is duplicating the dataset in its current expression elsewhere or duplicating the expression inherent in natural language or images (e.g., the prose of an IMDb review or an IMDb image).
As I understand it ...
Licences themselves are a mechanism to outline the terms under which the licensor agrees not to sue the licensee. Independent of the terms of the licence, the licensor needs some legal basis on which to sue for a licence to have any purpose. The relevant laws are (presumably) Intellectual Property laws. Wikipedia gives a broad list of such laws (under CC-BY-SA) ...
You can't patent the first name of the Queen of England or the run-length of the movie Dune. So let's skip patenting. And trademarking.
A more relevant law would seem to be copyright. But at least in the US, and I imagine in many other jurisdictions, you can't copyright the first name of the Queen of England or the run-length of the movie Dune either. Because copyright does not apply to facts. Here's a quote from the US copyright FAQ:
"Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed."
In a nutshell, copyright thus applies to expression, not to content. So okay, copyright can prevent you from copying the expression of the data verbatim (e.g., redistribute the exact PDF or the exact Excel sheet or idiosyncracies of the HTML page or an image or the exact text of some prose) but does not protect the factual content itself. If the data are mapped into a generic format like CSV, JSON, RDF, etc., copyright seems to have no jurisdiction over data.
So if not copyright, what else?
None of the other IP laws listed above seem relevant, except for the one you can see I clicked on from the image above: database rights. It seems that database rights vary widely from jurisdiction to jurisdiction. US database rights consider factual content as out of scope. Only the EU has database rights that should be of concern, here quoting from the Wikipedia article:
"While copyright protects the creativity of an author, database rights specifically protect the "qualitatively and/or quantitatively [a] substantial investment in either the obtaining, verification or presentation of the contents"
The EU database rights seem a little more "strong" than copyright in that they explicitly apply to databases storing factual content, but other than protecting the database as a complete curated package (i.e., the contextual/physical schema and its extension as tables), it does not protect the individual items of content in the database. You cannot just put a bunch of content into a database and then say that those contents are protected under database rights: precedent for people annoyingly trying to do this suggests that that's not how the law works.
Aside from IP, another possible legal facet is the Terms of Service/Acceptable Usage document you must implicitly/explicitly agree to when visiting the site to get the data, but other than banning the user from returning to a site or stopping them from accessing a service, I see no legal grounds on which a user can be sued for using a publicly downloadable dataset (again, other than infringing on the copyright of its expression).
So, assuming I'm not going to re-distribute the dataset with the same "expression" or re-use any creative elements likes images or prose writing ... assuming I'm only interested in using the factual content, my question then is:
Why should I care how a structured dataset is licenced?
The only meaningful answer I've come across so far is "so you know someone isn't going to try and sue you", which though a strong practical argument, I don't find conceptually compelling.
(I would be particularly interested in precedents where a party was successfully sued for using the factual content of a structured dataset that was not openly licenced.)