Create a TXT extention of CQL

One of the things that blocks wider acceptance of the excellent CQL code is the limited scope of the common query language. In GeoTools we have a more relaxed view of a filter; and it would be nice to make a TXT format that matches what we can do!

Here is what our new TXT format needs to do (over and beyond the current abilities of CQL):

1. support for spatial and comparison filters between any two expressions (CQL is limited to: propertyName OP expr)
   • CQL: propertyName contains geometry
   • TXT: geometry contains geometry
2. support for the Id filters as defined by Filter 1.0 specification
   • CQL: n/q
   • TXT: #road.1, #road.2

This request is for a new grammar (called TXT) that extends the CQL BNF to account for these ideas. The new format should be presented as a seperate facade class (even though behind the scenes it will share a lot of code with the normal CQL implementation classes).

The new TXT grammar facade class is method compatible with CQL facade class:

class TXT {
    String toTXT( Expression );
    String toTXT( Filter );
    Expression toExpression( String );
    Expression toExpression( String, FilterFactory );
    Filter toFilter( String );
    Filter toFilter( String, FilterFactory );
    List<Filter> toFilterList(String);
    List<Filter> toFilterList(String,FilterFactory);
}

Existing specificaitons like CAT2 allow the specificaiton of a queryLanguage; if an application wishes to make this format available to the public it is advised that "txt" be a more expressive alternative queryLanaguage to "cql".

Here are some technical notes from Mauricio:

Here are some examples (requested from Maria):

• area( the_geom ) > 30,000
• #road.1,#road.2, #road.47