Heterogeneous distributed databases Which description best characterizes a heterogeneous distributed database system?
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AThe same DBMS is used at each site, and data are centralized rather than distributed.
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BThe same DBMS is used at each site, and data are distributed across nodes.
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CDifferent DBMS products are used at sites, and data are not distributed across nodes.
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DDifferent DBMS products are used at sites, and data are distributed across nodes with gateways/middleware to integrate them.
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ENo DBMS is used; only file shares connect sites.
Answer
Correct Answer: Different DBMS products are used at sites, and data are distributed across nodes with gateways/middleware to integrate them.
Explanation
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:
1) Identify “heterogeneous” → different DBMS products.2) Confirm data are distributed, not centralized.3) Integration relies on gateways or federation middleware.4) Select the option that matches all three aspects.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.