Abstract: A Data Constraint Engine (100) for enforcing data constraints in a polyglot data tier (20) having a plurality of database-specific data stores (21, 22, 23) of various types such as an RDBMS (21), a Triplestore (22), and a MongoDB (23). The Data Constraint Engine uses the concept of a unified data model based on “records” in order to allow data constraints to be defined (using so-called “record shapes”) in a store-agnostic way. The Data Constraint Engine includes APIs (130) for processing incoming requests from remote clients (30) relating to data in the polyglot data tier, for example a request to create or update data in a data store. The APIs extract, from such a request, a record corresponding to the data specified in the request and a data source identifier identifying the data store holding the specified data. Then, on the basis of the record extracted by the interface, an appropriate record shape is extracted from a shapes catalogue (110), the record shape determining the structure of the record.

Abstract: A query mediator arranged to query a polyglot data tier of data stores, each data store adopting a data model and the polyglot data tier including at least two different types of data store with differing data models. The query mediator including at least one HTTP API; a catalogue containing metadata for each data store; and a plurality of adapters, one for each data model. The API receives an incoming query from a client, checks the query against the catalogue to identify a correct data store storing the queried data, and routes the query to an adapter for the correct data store. The adapter transforms the query into a format suitable for use with the data model adopted in the correct data store, for execution by the relevant data store. The API returns the query result to the client in response to the incoming query.