Rules Grammar

The rules validation system is an implementation of the RETS 1.8 specification for Validation Expressions. The design consists of three key components: a Field that the rule is defined for (E.g. ListPrice), a keyword or Action (as used in spark) to apply to the Field and (optionally) an Expression for determining if or how to apply the Action. The expression language is documented here for reference.

The following grammar is spark's implementation of the expression grammar referenced in the RETS specification. The expression language provides a means to express criteria for requiring an Action, or to set the value for a rule's Field. The Expression may reference the rule's Field or other fields to enable the rule builder to access the new or existing values for a resource.

RESO 1.8 Grammar Rules Implementation

This document explains the grammar rules for the rules expression language syntax. We take a few shortcuts to accomodate a LALR(1) implentation using RACC. Refer back to the full spec in the RESO_1.8.md reference document.

Grammar Rules

Root: Each expression is a full fledged expression result

   rule
     target
       : exp
       | /* none */ 
       ;

Expressions

Expressions are boolean or arithemetic operations, or special system functions that return a literal value.

   exp
     : orExp
     ;

Conjunctive expressions using .AND. or .OR..

   orExp
     : andExp
     | andExp OR andExp 
     ;
   andExp 
     : notExp
     | andExp AND notExp 
     ;

Logic expressions using .NOT., =, !=, >, >=, <, <=, .CONTAINS. or .IN..

   notExp 
     : eqExpr
     | NOT notExp 
     ;
   eqExpr
     : cmpExp
     | cmpExp EQ cmpExp 
     | cmpExp NE cmpExp 
     ;
   cmpExp
     : cntExp
     | cntExp GE cntExp 
     | cntExp LE cntExp  
     | cntExp LT cntExp 
     | cntExp GT cntExp 
     ;
   cntExp
     : sumExp
     | sumExp CONTAINS sumExp 
     | sumExp IN list       
     | sumExp IN funcExp    
     ;

Arithmetic expressions using +, -, *, / or %.

   sumExp
     : prodExp
     | sumExp PLUS prodExp  
     | sumExp MINUS prodExp 
     | sumExp CONCAT prodExp 
     ;
   prodExp
     : atomExp
     | prodExp MULTIPLY atomExp 
     | prodExp DIVIDE atomExp   
     | prodExp MODULUS atomExp  
     ;

Functions

Functions can take the place of an expression and must have a single return type (although some may return an list of one type). | Name | Description | Example | |---|---|---| | customField | Find a custom field for the record being processed. This function requires a group name and field name. | customField('Group Name', 'Field Name') | | getOldValue | Return the existing value of a field. | getOldValue(StandardStatus) = 'Pending' .AND. StandardStatus = 'Active' | | IFF | Return one of two possible values based on a condition. | IFF(ListPrice > 0.0 .AND. StandardStatus = 'Active', .EMPTY., .ENTRY.) | | LOOKUP | Returns the current restricted list of values for a PICKLIST field, as it has been modified by any SET_PICKLIST or RESTRICT_PICKLIST actions. | LOOKUP(City) | | LOWER | Convert a character value to lowercase | LOWER('Fargo') = 'fargo' | | PICKLIST | Return all the list values for a single field. For fields that require a related field, the function supports passing this field as a second parameter. | PICKLIST(PostalCode,City) | | STRLEN | Return the length of a character string | STRLEN('Fargo') = 5 | | SUBSTR | Return a portion of a character string. The second parameter is a 1-indexe location to start, and the option final parameter is for the length of the substring. | SUBSTR('Fargo', 2, 3) = 'arg | | TYPE | Return the type of the field as a character string (one of 'CHAR', 'INT', 'FLOAT', 'TIME','DATE','TIMESTAMP', 'BOOLEAN', and 'PICKLIST') The types are a string reflecting their namings as defined in 11.4.9.1 of the RETS 1.8 document | TYPE(City) = 'CHAR' | | UPPER | Convert a character value to uppercase | UPPER('Fargo') = 'FARGO' |

   funcExp
     : func LPAR params RPAR 
     ;
   func
     : FUNCTION
     ;

Nesting

This rule handles wrapping nested values and expressions

   atomExp
     : list
     | value
     | funcExp
     ;

Lists

Lists are used for .IN. actions. They differ from nested expressions in that they are comma delimmited and are associated with a list action. They are similar to function parameters, but those are processed separately below.

   list
     : LPAR RPAR             
     | LPAR list_items RPAR  
     ;
   list_items
     : exp
     | list_items COMMA exp 
     ;

Params

Parameters are specifically for function input. These can be expressions, but they are evaluated prior to calling the function.

   params
     : param
     | params COMMA param 
     ;
   param
     : exp
     ;

Values

Values contain literals, fields and special context values. These are static in nature and should generally be predetermined before the rule evaluation begins.

   value
     : specValue
     | charValue
     | intValue
     | floatValue
     | fieldName
     | timeValue
     | timeSpanValue
     ;

Variables

Variable special values are either user or rule specific. For example, use .OLDVALUE. to access the old record value of the current rule field.

   specValue
     : TRUE     
     | FALSE    
     | VARIABLE 
     | NULL 
     ;
   charValue:   CHARACTER ;
   intValue:    INTEGER   ;
   floatValue:  DECIMAL   ;

Dates and Times

Dates and times have a few supported formats.

  • RETSDATETIME ::= date-time | partial-date-time
  • RETSTIME ::= full-time | partial-time
  • DATE ::= Date using the format defined in RFC 2616 as rfc1123-date
   timeValue
     : RETSDATETIME 
     | DATE         
     ;

timeSpanValue: this is something mentioned in the grammar, but no syntax is defined. I'm going to assume this represents a time with no date component, as marked by RETSTIME. If I'm wrong, we'll just need to roll with it.

   timeSpanValue
     : RETSTIME     
     ;

Fields

The field names refer to the value of the field in the new record. Accessing the old record is possible using the getOldValue(FieldName) function.

   fieldName
     : FIELD 
     ;