Queries#

The accounting team wants unresolved invoices for customers whose payments are on hold. The invoice describes the dispute, while the customer carries the payment restriction. Neither record alone answers the question. A query brings those facts together without copying the customer's payment state into every invoice.

Relationships#

The question describes conditions the answer must satisfy. An entity must be an invoice, its dispute must be unresolved, and its customer must have payments on hold. The tags and predicates introduced in Fields can describe these conditions across related entities. The result identifies the invoices relevant to the work before the application starts processing them.

New questions can connect information that the original application never considered together. The investigation team might later ask whether those disputes concern items supplied by the same organization. That question adds another relationship to the existing information. Asking it should not depend on defining a new aggregate type or restructuring the invoices around the investigation.

The answer also needs a form suited to its consumer. An investigator may want each invoice with its customer and disputed items, while a report needs a count for each customer. The question includes which information matters and how the result should be organized. Different views can draw on the same facts without requiring separate versions of those facts for each use.

Shared definitions#

A question can become part of the application's business vocabulary. If two teams separately define an "unresolved invoice," they can disagree about whether a reopened dispute belongs in the result. A shared query gives them a definition they can examine together. Teams using different languages and stacks can use that definition instead of independently recreating its conditions.

The definition can develop as the business learns. A revised policy might add another condition to the invoices eligible for investigation. Keeping the query as data gives that revision a history alongside the invoices it selects, as described in Reification. An explanation of a changed answer can then consider changes to the question as well as changes to the facts.

An investigation view needs to change when disputes are resolved or reopened. A live query lets the application follow the answer to the same question as the data changes. The accounting service and investigation view can then follow the same definition as the facts change.