This paper explores the use of quasi serializable executions to maintain transaction consistency in heterogeneous distributed database systems (HDDBSs). The authors introduce the concept of quasi serializability, which is a correctness criterion for concurrency control in HDDBSs. Unlike serializability, quasi serializability does not impose requirements on the execution of local transactions at different sites, allowing for greater autonomy. The paper identifies aspects of transaction consistency that can be effectively maintained by quasi serializable executions and proposes techniques to prevent violations of these aspects. Key results include: 1. **Transaction Consistency with Quasi Serializable Executions**: Quasi serializable executions maintain transaction consistency for global transactions and transactions within the same local execution. However, they may violate consistency for transactions in different local executions. 2. **Maintaining Acyclicity of Distributed Interference**: The paper discusses methods to ensure the acyclicity of distributed interference relations, which is crucial for maintaining transaction consistency. This can be achieved by imposing restrictions on the remote value dependency of global transactions or by leveraging site-level information flow restrictions. 3. **Conclusion**: Quasi serializability is presented as a promising approach for concurrency control in HDDBSs, offering both effective maintenance of local autonomy and assurance of system consistency with controlled global transactions. The paper also includes an example of an international banking system to illustrate the concepts and provides a detailed mathematical framework for analyzing transaction consistency in HDDBSs.This paper explores the use of quasi serializable executions to maintain transaction consistency in heterogeneous distributed database systems (HDDBSs). The authors introduce the concept of quasi serializability, which is a correctness criterion for concurrency control in HDDBSs. Unlike serializability, quasi serializability does not impose requirements on the execution of local transactions at different sites, allowing for greater autonomy. The paper identifies aspects of transaction consistency that can be effectively maintained by quasi serializable executions and proposes techniques to prevent violations of these aspects. Key results include: 1. **Transaction Consistency with Quasi Serializable Executions**: Quasi serializable executions maintain transaction consistency for global transactions and transactions within the same local execution. However, they may violate consistency for transactions in different local executions. 2. **Maintaining Acyclicity of Distributed Interference**: The paper discusses methods to ensure the acyclicity of distributed interference relations, which is crucial for maintaining transaction consistency. This can be achieved by imposing restrictions on the remote value dependency of global transactions or by leveraging site-level information flow restrictions. 3. **Conclusion**: Quasi serializability is presented as a promising approach for concurrency control in HDDBSs, offering both effective maintenance of local autonomy and assurance of system consistency with controlled global transactions. The paper also includes an example of an international banking system to illustrate the concepts and provides a detailed mathematical framework for analyzing transaction consistency in HDDBSs.