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What Is Single Table Inheritance?

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  • Written By: Alex Newth
  • Edited By: A. Joseph
  • Last Modified Date: 13 November 2016
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    2003-2016
    Conjecture Corporation
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Single table inheritance is a coding method in which object-oriented inheritance, which usually is not included on a database program, is emulated for a relational database. By using this, the user will be able to see the relationship between many different labels within a single table, making it easier for users to digest or add to the data. If there are many null fields or if there are a large number of relations, using single table inheritance might return unexpected results that will confuse even advanced database designers. With this database inheritance schema, the single table shows the data in a hierarchical fashion.

Relational databases are databases that relate one group of data to another and typically have hierarchical maps. For example, if someone is searching for a book through a relational database, then he or she typically will find fields for author, genre, first letter of book and then a list of books. In normal instances, each field has its own table, and the tables rarely interact aside from mediating the user from one field to another.

In single table inheritance, all of the fields are displayed on one table. This is much easier to look at and easier to sift through. All of the data displayed in the table goes from the top to the bottom. This means that the author would be on the top of the single table, and the first letter of the book would be on the bottom.

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Creating a single table inheritance model can be difficult at first, unless the database designer is familiar with the coding. Making a map from the database to separate objects in an object-oriented programming schema typically does this. There must be several classes, otherwise this will not group everything together into a single table.

Two types of problems might keep single table inheritance from working properly. One is if the objects represent a null value. If this occurs, then the null value will be sprinkled in with the valuable data in the inheritance table. This means that the table will display relevant information, but every few lines, or however often the null values occurs, the word “null” will show up nearby or underneath another value.

If the object being mapped has many hierarchies, especially hierarchies that are not similar, this also can cause a problem for single table inheritance. With many hierarchies, there is a chance that the designer might miss one, causing a relational error. If the hierarchies are not similar, then the relational database might have trouble understanding the mapping made between the data sets.

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