Updates to Filter Extension for CQL2

[philvarner]

Related Issue(s): #222

Proposed Changes:

• Filter Extension updates to align with changes to OAFeat CQL2 spec
• Updated all "CQL" usages to "CQL2"
• Most conformance class URIs are now prefixed with http://www.opengis.net/spec/cql2/ instead
  of http://www.opengis.net/spec/ogcapi-features-3/
• Conformance classes http://www.opengis.net/spec/ogcapi-features-3/1.0/conf/basic-cql,
  http://www.opengis.net/spec/ogcapi-features-3/1.0/conf/cql-text, and
  http://www.opengis.net/spec/ogcapi-features-3/1.0/conf/cql-json have had cql replaced
  with cql2 (in addition to the prefix change) to
  become http://www.opengis.net/spec/cql2/1.0/conf/basic-cql2,
  http://www.opengis.net/spec/cql2/1.0/conf/cql2-text, and
  http://www.opengis.net/spec/cql2/1.0/conf/cql2-json
• Significant changes to CQL2 JSON format, now using op and args structure
• Spatial operator INTERSECTS is now S_INTERSECTS
• Temporal operator ANYINTERACTS is now T_INTERSECTS
• Updated Example 3 (now Example 5) to make it clear that property to property comparisons require the
  Property-Property Comparisons conformance class
• Added CQL2 Case Insensitive Comparison
  (http://www.opengis.net/spec/cql2/1.0/conf/case-insensitive-comparison) conformance class
  that adds functions LOWER and UPPER for case-insensitive comparison

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes. THIS PR HAS BREAKING CHANGES
• This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.

[jisantuc]

Should review here wait on the symbolic operators change upstream?

[philvarner]

Should review here wait on the symbolic operators change upstream?

My understanding is that the current published spec allows either symbolic or alphabetic, and that's changing to only allow symbolic, so these are currently valid wrt that.

[m-mohr]

Quickly looked at it and looks good to me, but I leave the full review and final approval up to an implementor.

[bitner]

Looking good @philvarner!

I think it would be good to include examples for BETWEEN, IN and the use of UPPER/LOWER.

Having these examples is really helpful when building things out and also gives a great starting place for building out tests (ie these are used directly in the pgstac tests in the PR for adding CQL2 support)

[philvarner]

@bitner Added some examples for BETWEEN, IN, LIKE, UPPER, and LOWER. If you accept the invite for this repo, you may be able to approve the PR. Otherwise, @m-mohr or @cholmes, would you approve it based on @bitner's comments?

[bitner]

So upper and lower are implemented as "function" not with "op"?

As these are standard, shouldn't they use "op"? My impression is that "function" was for platform defined functions.

[philvarner]

Correct. They're not operators since they don't return a boolean value -- they return a string value. However, I looked it up in the spec and I did define them wrong -- they're not operators or functions, they're a separate thing, which is confusing, because the text syntax is exactly the same as if they were functions. I'll update the examples.

The spec is here:
https://github.com/opengeospatial/ogcapi-features/blob/b752479d850c52f372c4164202f041ecbe906e46/cql2/standard/schema/cql2.json

[philvarner]

I'm going to ask the CQL2 folks about this, because it seems like it would be simpler if it was just a pre-defined function.

[philvarner]

Filed this issue opengeospatial/ogcapi-features#656

[philvarner]

ah, so this is changing in CQL2 opengeospatial/ogcapi-features#641

UPPER/LOWER will be replaced with a function CASEI

[philvarner]

After looking at CASEI, I have some significant concerns about it. I'm just going to yank it for beta.5, and re-add after it's stabilitzed in CQL2. I wrote up the concerns here if you're interested
opengeospatial/ogcapi-features#641 (comment)