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DCP-5: Valids and restrictions for query elements

Progress

Submitted on: 24 Apr 2012
Review period: 24 Apr 2012 to 24 May 2012
Revision: TBD
Vote: http://www.doodle.com/rw4kg7w6yxc5yfdf - to end 2012-06-01, 12pm EDT. ish.
Final review: TBD
Ratified / Rejected: TBD

Facilitator: Ian Truslove (Ian Truslove (Truslove))

Description

Provide a mechanism to describe valid and invalid inputs for query elements in ESIP Discovery services.

Problem Addressed

OpenSearch does not have a mechanism for indicating valid options for search parameters. The OpenSearch Parameter extension (http://www.opensearch.org/Specifications/OpenSearch/Extensions/Parameter/1.0) has options for specifying the number of times a particular parameter may or should be included in the search request, but this does not meet our needs.

Proposed Solution

Add a validpatterns role to the OpenSearch <query> element, and specify valid values for attributes with a regular expression.

Example:

<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
  <Url type="application/atom+xml" template="http://somedataprovider.com/?q={searchTerms}&datum={datum?}&gridSize={gridSize}&format=atom"/>
  <Query role="example" searchTerms="map" datum="WGS84" gridSize="1km" />
  <Query role="http://esipfed.org/ns/discovery/1.1/#validpatterns" searchTerms="WGS84|EGM96" gridSize="1m|10m|100m|500m|1km|10km" />
</OpenSearchDescription>

Rationale for the Solution

Terse - a single parameter's options fit into a single attribute value.
Well-understood - this is the same mechanism HTML5 uses for input field validation (http://www.whatwg.org/specs/web-apps/current-work/multipage/common-input-element-attributes.html#the-pattern-attribute). Implementors will undoubtedly be familiar with this web technology.
Powerful - regular expressions are a powerful pattern matching mechanism.

Discussions

There are a proliferation of regex "flavors" - see http://www.regular-expressions.info/refflavors.html. We should standardize on one of these flavors.
- The HTML5 specification uses the ECMAScript flavor of regex. This seems a reasonable, standardized regex standard to implement as part of DCP-5.

Having now looked at the OS Parameters extension, I wonder if it makes sense to piggyback on that. The good thing there is that for each search parameter there is a <parameters:Parameter> tag that contains multiple attributes. One could add a 'pattern' attribute to contain the regular expression just as in the HTML <input> element. Or put the pattern attribute in a namespace if we can't get the author of the Parameters extension to agree.

My (small) objection to the current proposal is that putting the actual search parameter names as many new attributes in a <Query> tag seems kind of sketchy (risky?). By having a separate tag for each one, there is always room for further extension using more attributes.

Consensus

TBD

Voting results

TBD