Model

The Hilang model of person in the cousin's sample is a good example of the use of indexes. Each person has a reference to their mother and father, together with extension properties to mother's children and father's children. To support navigation from a person to their children indexes are created in the generated code for fast indexed access.

entity Cousins.Person
    = Node (),
      Edge  (From = this,   To = Mother, Name = Name, TypeName = "Mother"),
      Edge2 (From = this,   To = Father, Name = Name, TypeName = "Father"),
      Edge3 (From = Father, To = this,   Name = Name, TypeName = "Child"),
      Edge4 (From = Mother, To = this,   Name = Name, TypeName = "Child")
(
    Name        : String
)
{
    Gender      : Cousins.Gender,

    Mother      : Cousins.Person,
    Father      : Cousins.Person
}
[
    TypeName    = "Person",

    FatherChild : Cousins.Person (Father = this),  /* navigation creates an index */
    MotherChild : Cousins.Person (Mother = this),  /* navigation creates an index */
    @Once
    Relatives   = relation (this)
];

Sample family tree

When the graph is added to the CousinsSpace, Person key/value pairs are created for the data and Index key/value pairs for indexed access.

Type	│	Key	│	Value
Person	│	Name : Eve	│	Gender : Female
...	│	...	│	...
Person	│	Name :Jane	│	Gender : Female, Mother : Eve
MotherChild	│	Mother : Eve, Name Jane	│	Name : Jane
...	│	...	│	...
Person	│	Name :Adam	│	Gender : Male, Father : Jack
FatherChild	│	Father : Jack, Name : Adam	│	Name : Adam
...	│	...	│	...
Person	│	Name :Lucy	│	Gender : Female, Mother : Mary, Father : John
MotherChild	│	Mother : Mary, Name : Lucy	│	Name : Lucy
FatherChild	│	Father : John, Name : Lucy	│	Name : Lucy
...	│	...	│	...
Person	│	Name : Mark	│	Gender : Male, Mother : Mary, Father : John
MotherChild	│	Mother : Mary, Name : Mark	│	Name : Mark
FatherChild	│	Father : John, Name : Mark	│	Name : Mark
...	│	...	│	...

NB {Person, Name, Mother,Father, Gender, Female, Male, MotherChild, FatherChild} are not stored (as they would for JSON encoding), just the tag number from meta-model.

When we search a SetSpace ( like CousinSpace.Persons), a rule-based-optimizer is used:

Use the KeyPath if it is Sargable (At least the first field of the Key has a value).
Use the first Index that is Sargable (At least the first field of the Index Key has a value).
Scan all items of the type.

Search for Person { Name = "Lucy"} will access the Person directly in Hiperspace
Search for Person { Name = "Lucy", Mother: "Mary", Father: "John"} will access the Person directly in Hiperspace
Search for Person { Mother = "Mary"} will use the 1st index MotherChild to return 'Lucy' and 'Mark'
Search for Person { Father = "John"} will use the 2nd index FatherChild to return 'Lucy' and 'Mark'
Search for Person { Mother = "Mary", Father = "John"} will use the 1st index MotherChild to return 'Lucy' and 'Mark'