computer science

Single Table Inheritance

Single Table Inheritance is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Single Table Inheritance rather than just read about it. In short: Single table inheritance is a way to emulate object-oriented inheritance in a relational database. When mapping from a database table to an object in an object-oriented language, a field in the database identifies what class in the hierarchy the object belongs to.

Key takeaways

Single Table Inheritance belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Single Table Inheritance to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Single Table Inheritance from memory before moving on to harder problems.

Reference excerpt

Single table inheritance is a way to emulate object-oriented inheritance in a relational database. When mapping from a database table to an object in an object-oriented language, a field in the database identifies what class in the hierarchy the object belongs to. All fields of all the classes are stored in the same table, hence the name "Single Table Inheritance". In Ruby on Rails the field in the table called 'type' identifies the name of the class. In Hibernate (Java) and Entity Framework this pattern is called Table-Per-Class-Hierarchy and Table-Per-Hierarchy (TPH) respectively., and the column containing the class name is called the Discriminator column.

Example

The table have the Url which is used by all blogs but only blogs of type RssBlog have a value assigned in the RssUrl column, other rows have NULL.

See also Object–relational mapping ActiveRecord (Rails)

References

External links Single Table Inheritance Single Table Inheritance in Yii Single Table Inheritance in Django

Worked examples

Example 1 — a first encounter with Single Table Inheritance

Start with the simplest possible case. Write down what Single Table Inheritance claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Single Table Inheritance before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Single Table Inheritance ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Single Table Inheritance

In research: Single Table Inheritance appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Single Table Inheritance in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Single Table Inheritance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Database theory, Software engineering stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Single Table Inheritance outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Single Table Inheritance in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Single Table Inheritance means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Single Table Inheritance out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Single Table Inheritance in simple terms?

Why does Single Table Inheritance matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Single Table Inheritance?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Single Table Inheritance.