...CONSTRAINTLANGUAGE=CQL_TEXTCONSTRAINT=”prop1=10”...
The value of the CONSTRAINT parameter in the KVP encoding may also include an XML encoded Filter expression although some clients may impose length limitations.
10.8.4.11 OGC filter syntax 10.8.4.11.1 Introduction
The XML implementation of the BNF in Subclause 6.3.2 may be found in OGC document 04-095, Filter Encoding Implementation Specification. The intent of the XML
encoding of the OGC common query language is that it be easily parsable using readily available XML parsers and be easily translatable into a target predicate language such as
a SQL where clause or an XQuery predicate.
10.8.4.11.2 Provide functional extensibility
One feature of the OGC common query language and the XML implementation is that the predicate language is functionally extensible. This means that functions may be added
to the filter predicate language without having to change the underlying schema. The relevant schema fragment from OGC 04-095 is:
xsd:element name=Function type=ogc:FunctionType
substitutionGroup=ogc:expression xsd:complexType name=FunctionType
xsd:complexContent xsd:extension base=ogc:ExpressionType
xsd:sequence xsd:element ref=ogc:expression
minOccurs=0 maxOccurs=unbounded xsd:sequence
xsd:attribute name=name type=xsd:string use=required xsd:extension
xsd:complexContent xsd:complexType
According to the schema fragment, any function may added to the filter predicate language simply by specifying its name and including zero or more ogc expressions as
content of the Function element which represent the arguments of the function. The following example shows how a function may be called using the filter syntax:
Function name=”MAX” PropertyNameDEPTHPropertyName
Function
In this example, the MAX function is invoked to find the maximum value of the property DEPTH.
Any function may be called using the filter syntax as long as the function is advertised in the filter capabilities section Clause 16 of OGC 04-095 of an OGC capabilities
document.
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10.8.4.11.3 Precedence
The XML notation does not provide parentheses to indicate operator precedence as specified in the BNF. The Filter Specification uses the nested structure of the XML
notation to indicate this relationship.
In this example, a more complex scalar predicate is encoded using the logical operators AND and OR. The example is equivalent to the expression FIELD1=10 OR
FIELD1=20 AND STATUS=VALID:
Filter xmlns=http:http:www.opengis.netogc xmlns:foo=“http:www.someverser.comfoo”
And Or
PropertyIsEqualTo PropertyNamefoo:FIELD1PropertyName
Literal10Literal PropertyIsEqualTo
PropertyIsEqualTo PropertyNamefoo:FIELD1PropertyName
Literal20Literal PropertyIsEqualTo
Or PropertyIsEqualTo
PropertyNamefoo:STATUSPropertyName LiteralVALIDLiteral
PropertyIsEqualTo And
Filter
10.8.4.11.4 Tight and loose queries
