Semantic Heterogeneity basically occurs when schema or data set for same domain is developed by independent parties which leads to differences in meaning, interpretation and intended use of the same or related data. Semantic Heterogeneity among components database system basically creates the biggest hurdle in designing global schemas of the heterogeneous database. The design autonomy of components DBSs refers to their freedom of choosing the following design parameters which in turn affect the eventual complexity of the FDBSs.
- Universe of discourse from which data is drawn –
For example, two customer accounts, databases in the federation may be from united states and china with entirely different sets of attributes about customer accounts required by the accounting practices required by the accounting practices. Currency rate fluctuations would also present a problem. Hence relations in two databases which have the identical names-Customer or Account may have some common and some entirely different information.
- Representation and Naming –
The representation and naming of the data elements and the structure of the data model may be prespecified for each local database.
- The understanding, meaning and subjective interpretation of data –
This is a chief contributor to semantic heterogeneity.
- Transaction and policy constraint –
These deal with serializability criteria, compensating transaction and other transaction policies.
- Derivation of summaries –
Derivation of summaries basically has Aggregation, summarization and other data-processing features and operations which are supported by the system.