Impara Ontologies, Schemas, and Constraints | Foundations of Knowledge Graphs

Ontologies and schemas are essential for structuring and interpreting information in knowledge graphs. An ontology defines the types of entities, relationships, and the general rules for how knowledge is organized within a particular domain. It provides a shared vocabulary and a formal structure for representing knowledge, ensuring consistency and interoperability. A schema is closely related: it specifies the allowed entity types, relation types, and constraints that must be satisfied by the data in the knowledge graph. The schema acts as a blueprint, guiding both the creation and validation of triples, so that all data fits the intended structure and meaning.

Definition

Domain and range constraints specify which types of entities can appear as the subject (domain) and object (range) of a particular relation in a knowledge graph. For example, if a relation authored has domain Person and range Book, then only entities of type Person can be authors, and only entities of type Book can be authored.


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# Define entity types
entity_types = ["Person", "Book", "City"]

# Define relations with domain and range constraints
relations = {
    "authored": {"domain": "Person", "range": "Book"},
    "born_in": {"domain": "Person", "range": "City"},
    "located_in": {"domain": "Book", "range": "City"}
}

# Example: Check if a triple satisfies the constraints
def is_valid_triple(subject_type, relation, object_type):
    constraint = relations.get(relation)
    if not constraint:
        return False
    return constraint["domain"] == subject_type and constraint["range"] == object_type

# Test
print(is_valid_triple("Person", "authored", "Book"))  # True
print(is_valid_triple("Book", "authored", "Person"))  # False
print(is_valid_triple("Person", "born_in", "City"))   # True

1. What is the purpose of a schema in a knowledge graph?

2. How do domain and range constraints affect triples?

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Sezione 1. Capitolo 3

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