Building a Graph From Tabular Relationship Data

Almost every graph starts life as relational tables. The conversion is mechanical once three decisions are made, and one of the three — id remapping — is a silent correctness bug rather than a matter of taste. Deciding what is a node Start with three tables: customers (customer_id, region, signup_date, tenure_days), products (product_id, category, price), and orders (order_id, customer_id, product_id, amount, ordered_at). The rule that resolves nearly every case: A table with a primary key that other tables point at is a node type. A table whose whole job is to link two keys is an edge type. So customers and products are nodes, and orders are edges — even though orders has its own primary key. The order id is not an entity you want to reason about; it is an identifier for a relationship. The harder case is a repeated categorical column such as region . It can stay a customer feature, or it can become a node type with a customer–region edge. The test is behavioural, not aesthetic: do you want information to flow between rows that share this value? As a feature, region is a tag on each customer and nothing more. As a node, it creates a two-hop path between every pair of customers in the same region, so their representations start blending. If a region contains 400,000 customers, that node is a hub through which everything mixes, which is usually a way of turning four hundred thousand distinct customers into one regional average. Keep high-cardinality-of-membership categoricals as features; promote a category to a node when its membership is small and meaningful. If you end up with more than one node type, the model has to change too — see heterogeneous graph neural networks . The id remapping nobody warns you about Graph libraries do not store your ids. They store a node feature matrix and an edge index of integer positions into it, because a message-passing layer is a gather over rows of a dense array. So node ids must be contiguous integers from 0 to n−1 , per node