ATP Condition Expression Syntax v1
SDK Architecture Blueprint · Section 7 · OQ-AS-1 Resolution
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7. ATP Condition Expression Syntax v1 — Full Grammar (OQ-AS-1)
7.1 Background
The ATP Condition Expression Syntax is used in the PricingRule fragment (Fragment 14) to express conditions that reference Collection and Configuration schema fields. Session 3.5 defined the v1 syntax informally with worked examples. OQ-AS-1 deferred the full grammar and parser specification to Session 7.
The syntax is intentionally narrow. It is not a general-purpose expression language. It is constrained to the field reference and comparison cases required by the Activity Configuration Schema Starter Catalogue. This constraint is a deliberate design decision: AI agents must be able to evaluate conditions reliably without ambiguity, and the grammar must be implementable by a simple recursive-descent parser.
7.2 Grammar (EBNF)
+-----------------------------------------------------------------------+ | (* ATP Condition Expression Syntax v1 — EBNF *) | | | | expression ::= or_expr ; | | | | or_expr ::= and_expr ( 'OR' and_expr )* ; | | | | and_expr ::= not_expr ( 'AND' not_expr )* ; | | | | not_expr ::= 'NOT' not_expr | comparison ; | | | | comparison ::= field_ref operator literal | | | | | field_ref 'IN' '[' literal_list ']' ; | | | | field_ref ::= segment ( '.' segment )* ; | | | | segment ::= identifier | 'participant' | 'collection' ; | | | | identifier ::= [a-zA-Z_][a-zA-Z0-9_]* ; | | | | operator ::= '==' | '!=' | '>' | '<' | '>=' | | | '<=' ; | | | | literal ::= string_literal | number_literal | boolean_literal | | | enum_literal ; | | | | string_literal ::= '"' [^"]* '"' ; | | | | number_literal ::= '-'? [0-9]+ ( '.' [0-9]+ )? ; | | | | boolean_literal ::= 'true' | 'false' ; | | | | enum_literal ::= identifier ; (* uppercase by convention *) | | | | literal_list ::= literal ( ',' literal )* ; | | | | (* Whitespace is insignificant and ignored between tokens. *) | | | | (* Keywords: AND OR NOT IN true false — case-sensitive, uppercase. | | *) | +-----------------------------------------------------------------------+
Decision CES-1 (CLOSED): The ATP Condition Expression Syntax v1 grammar is as specified above. The grammar is normative for all PricingRule condition fields in the Activity Configuration Schema. The parser MUST reject any expression that does not conform to this grammar.
7.3 Field Reference Semantics
Field references use dot notation to navigate the schema hierarchy. The following prefixes are defined:
Prefix Resolves to
collection.participant.{field} Each participant in the booking Collection. When evaluated against a multi-participant collection, the condition is true if ANY participant satisfies it (existential quantification).
collection.{field} Top-level Collection fields (e.g. collection.group_size).
configuration.{field} Configuration-layer fields for the activity.
capability.{field} Capability-layer fields (read-only in pricing context).
Absent fields evaluate to null. A comparison with a null field always evaluates to false. Parsers MUST NOT throw on absent fields — they MUST evaluate the condition as false.
7.4 Worked Examples
Ski instructor fee trigger (from Starter Catalogue SKI_ALPINE):
+-----------------------------------------------------------------------+ | collection.participant.skill_domain == SKIING | | | | AND collection.participant.self_assessed_level IN [NEVER, BEGINNER] | | | | AND collection.participant.instructor_requested == true | +-----------------------------------------------------------------------+
Tall child adult-gear surcharge:
+-----------------------------------------------------------------------+ | collection.participant.height_cm >= 150 | | | | AND collection.participant.age_band == CHILD | +-----------------------------------------------------------------------+
Group size minimum for private tour:
collection.group_size < configuration.min_private_group_size
These examples cover all comparison and IN-list cases in the Starter Catalogue. The grammar is sufficient for all v1.0 PricingRule cases. OQ-AS-1 is resolved.
7.5 Parser Specification
The @atp/core package exports a reference parser:
+-----------------------------------------------------------------------+ | // @atp/core — Condition Expression parser | | | | export function parseConditionExpression(source: string): | | ConditionExpression; | | | | export function evaluateConditionExpression( | | | | expr: ConditionExpression, | | | | context: ConditionEvaluationContext | | | | ): boolean; | | | | export interface ConditionEvaluationContext { | | | | collection: CollectionRecord; | | | | configuration: ConfigurationRecord; | | | | capability: CapabilityRecord; | | | | } | | | | // Thrown by parseConditionExpression on grammar violation | | | | export class ConditionExpressionParseError extends ATPError { | | | | source: string; // Original expression string | | | | position: number; // Character position of error | | | | expected: string; // What the parser expected | | | | } | +-----------------------------------------------------------------------+
Decision CES-2 (CLOSED): The Condition Expression parser is part of @atp/core (zero external dependencies). It is a recursive-descent parser. The parser is the normative reference implementation. Any ATP-compatible implementation that evaluates PricingRule conditions MUST produce results identical to this parser for all conforming expressions.
Decision CES-3 (CLOSED): The Condition Expression Syntax is versioned independently of the protocol. The v1 grammar is frozen at publication. New operators or field reference patterns require a v2 grammar. The @atp/core parser exports a version string ("atp-ces/1.0") that implementations MUST include in interop test results.
7.6 OQ-AS-1 — Resolution
+-----------------------------------------------------------------------+ | DECISION OQ-AS-1 — RESOLVED (CLOSED) | | | | ATP Condition Expression Syntax v1 — full grammar and parser | | specification. | | | | RESOLVED. The full EBNF grammar is specified in Section 7.2. Field | | reference semantics are specified in Section 7.3. The reference | | parser is exported from @atp/core as parseConditionExpression and | | evaluateConditionExpression. Three decisions closed: CES-1 through | | CES-3. The v1 grammar is sufficient for all Starter Catalogue | | PricingRule cases. | +-----------------------------------------------------------------------+