no need to create new GitHub ISSUE for access to literal value from URI template

Hi - at yesterday’s weekly teleconf [1] we talked about needing to access the literal value from a cell from a URI template. 

The example cited relates to the use of multiple missing values: e.g. tokens `unknown` and `withheld` are both “null” values, but mean different things. Given occurrence of either of these tokens in a dataset, the cell value would be assumed to be null (empty). I had argued that one might want to use a URI template (in a virtual column) to include information in, say, an RDF conversion about _why_ the data value was missing. Given that URI templates operate on the _canonical value_ of the cell (not the literal value), the cell value in these situations would already be set to an empty string “” and thus unable to use the `unknown` or `withheld` assertion.

I agreed to open a new ISSUE in GitHub for this.

However, having thought about this further, my scenario is flawed: without if/then/else logic my URI template would be triggered for _every row_ - including those rows with non-null values too. Yuk.

@JeniT noted that the “unions of datatypes” approach (see ISSUE #223 [2]) might be a better fit for this problem - which is possible. Alternatively, it seems that if this is important for data publishers, it would be appropriate for them to include an additional "nil-reason” column in their data to document this kind of information rather than trying to overload a single column! 

I can’t think of another reason as to why I would want to access the literal cell value from a URI template - so I don’t think it’s pertinent to open the new ISSUE … and I haven’t! Please advise if you feel otherwise.

Jeremy

[1]: http://www.w3.org/2015/02/25-csvw-minutes.html <http://www.w3.org/2015/02/25-csvw-minutes.html>
[2]: https://github.com/w3c/csvw/issues/223 <https://github.com/w3c/csvw/issues/223>