scope of PQL
patrick.dowler at nrc-cnrc.gc.ca
Tue Feb 24 10:21:12 PST 2009
Now that the way forward is clear, we need to define the scope of the PQL
document and decide if we should rename it.
At a minimum, P?? is a set of parameters that are are defined consistently and
then used by multiple DAL services. The goal is simply that there is only one
meaning for a specific parameter name and there is a definitive document that
specifies it. It is clear that specific service specifications must extend
this with either additional parameters (as in SSA) or by defining
standard "property names" to be used with WHERE.
At the other end, one could formalise PQL into a query language along the
lines of query-by-example or some sort of template-matching scheme. This
would be a smaller scope but a (more) complete query language.
As it stands right now:
* P?? includes the specification of the syntax for range (/) and list (,)
values, qualifiers (;) and symbolic values (@ and/or $).
* P?? includes the standard query parameters (POS, SIZE, BAND, TIME, REGION).
* P?? includes FROM for use by services with multiple things to query
(currently only TAP, but could be others since "multiple things to query" is
dependent on what the data model looks like). It also includes WHERE for
cases where services expose "names" of things via metadata (columns in TAP)
or where they standardise these "names" (utypes maybe) in the spec or a
related document (a data model). I think these could have use beyond TAP.
Should P?? include non-query parameters? Specifically, I am thinking about
MAXREC, MTIME, FORMAT. These are used in multiple specs.
Should P?? include standardised way to upload things, without saying what they
are? That is, standardise the UPLOAD=name,URI parameter? Standardise the
inline upload (and where the name comes from in there)?
Basically, is P?? limited to the what is needed to pose a query or is it
generally "all the standard DAL parameters"?
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