Data Retrieval for Heterogeneous Data Models

  • Prakash M. Nadkarni
Part of the Health Informatics book series (HI)


Retrieving data from a heterogeneously modeled database is understandably complex because the same conceptual operation requires different types of queries depending on how the class of data that you wish to retrieve is physically organized. Thus: 1. For conventional (columnar)-structured data, the conceptual operation and the query mechanism are identical. A a query that fetches only attributes of interest (i.e., without aggregates), even across multiple tables, can usually be effected with a single SQL statement that has a simple structure – that is, it has no subqueries. 2. For EAV-structured data, query of data based on combinations of values of attributes takes many more steps than for columnar (traditionally modeled) data: the AND, OR and NOT operations must be substituted respectively by the set operations of intersection, union and difference. 3. For hybrid classes, a combination of approaches would be necessary, based on whether the attributes you are fetching are columnar or EAV-modeled. 4. Querying a mixture of conventional, EAV, and hybrid classes is the most difficult. It requires decomposing the query task into individual operations on each class, and then combining the results.


Hash Table Output Table Personal Health Information Temporary Table Query Tool 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag London Limited 2011

Authors and Affiliations

  • Prakash M. Nadkarni
    • 1
  1. 1.School of MedicineYale UniversityNew HavenUSA

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