Heterogeneous distributed databases Which description best characterizes a heterogeneous distributed database system?

Introduction / Context:
Heterogeneous distributed databases integrate multiple DBMS products—often with different SQL dialects, data types, and transaction semantics—into a single logical database. Middleware, gateways, or federation layers reconcile differences to provide location and, at times, heterogeneity transparency to applications.

Given Data / Assumptions:

• Multiple DBMS engines (e.g., Oracle, PostgreSQL, SQL Server) participate.
• Data are physically distributed across sites.
• A coordination layer provides a global schema and routing.

Concept / Approach:

The defining trait is differing DBMSs across nodes. Distribution still applies; otherwise, it would not be a distributed database. Integrating unlike systems requires translation (SQL dialects, type mappings), metadata federation, and distributed transaction coordination where supported.

Step-by-Step Solution:

Verification / Alternative check:

Federated database systems and heterogeneous DDBMS designs are documented to use wrappers/gateways (e.g., Oracle Database Links, SQL Server Linked Servers, foreign data wrappers) to bridge engines.

Why Other Options Are Wrong:

• Options a/b: homogeneous, not heterogeneous.
• Option c: not distributed (contradicts the premise).
• Option e: lacks DBMS-level distribution semantics.

Common Pitfalls:

• Assuming full ACID across heterogeneous engines is automatic; capabilities vary.

Final Answer:

Different DBMS products are used at sites, and data are distributed across nodes with gateways/middleware to integrate them.