Cardinal Query Language

Language Description

CQL (Cardinal Query Language) is a simple query language that queries entities based on components contained in the entity.

Components

The language uses the names of Components to specify the entities you are interested in querying.

Examples:

• healthComponent
• attackComponent
• armComponent
• legComponent

Functions

Two functions are provided in the language that accept a variadic amount of components as parameters

EXACT(…) and CONTAINS(…)

CONTAINS(...)

CONTAINS is a query for entities that only need to "contain" the specified components. If an entity has more components than just the specified component(s), it is still a valid entity for that query.

Examples:

• CONTAINS(armComponent) is a query for all entities that have a arm component. The entity can have more components than just the arm.
• CONTAINS(armComponent, legComponent) is query for all entities that have both an arm component and a leg component. The entity can have more components than the arm and the leg.

EXACT(...)

EXACT is a query for entities that contain "exactly" the specified the components. Nothing more nothing less.

Examples:

• EXACT(healthComponent) is a query for all entities with exactly one health component; nothing more.
• EXACT(healthComponent, attackComponent) is a query for all entities with exactly one health component and one attack component; nothing more.

Operators

CQL provides three logical operators: &, | and !

! negates a query.

• Example: !CONTAINS(healthComponent) queries all entities that do not contain a health component.

& performs the "and" operation on two queries.

• Example: CONTAINS(healthComponent) & !CONTAINS(attackComponent) is a query for all entities that contain a health component "and" does not contain an attack component

| performs the "or" operation on two queries.

• Example: CONTAINS(healthComponent) | !CONTAINS(attackComponent) is a query for all entities that either contains a health component "or" does not contain an attack component

Operators in CQL do not have any intrinsic precedence. All expressions are consumed from left to right.

• Example: A & B | C & D | F is equivalent to ( ( A & B ) | C ) & D ) | F)

You can use parenthesis to specify and change precedence in CQL.

• Example: EXACT(legComponent) | (!CONTAIN(healthComponent) & !CONTAIN(attackComponent))

  • The above is a query for either an entity with only a leg component or an entity that does not have a health component and also does not have an attack component.

• Example: (EXACT(legComponent) | !CONTAIN(healthComponent)) & !CONTAIN(attackComponent)

  • The above is the same query but with precedence changed. Now it is querying an entity with either exactly one leg component or does not have a have a health component. Additionally that entity must not ever contain a attack component.

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