computer science

Relvar

Relvar 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 Relvar rather than just read about it. In short: In relational databases, relvar is a term introduced by C. J.

Key takeaways

Relvar 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 Relvar to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Relvar from memory before moving on to harder problems.

Reference excerpt

In relational databases, relvar is a term introduced by C. J. Date and Hugh Darwen as an abbreviation for relation variable in their 1995 paper The Third Manifesto, to avoid the confusion sometimes arising from the use of the term "relation", by the inventor of the relational model, E. F. Codd, for a variable to which a relation is assigned as well as for the relation itself. The term is used in Date's well-known database textbook An Introduction to Database Systems and in various other books authored or coauthored by him. Some database textbooks use the term relation for both the variable and the data it contains. Similarly, texts on SQL tend to use the term table for both purposes, though the qualified term base table is used in the standard for the variable. A closely related term often used in academic texts is relation schema, this being a set of attributes paired with a set of constraints, together defining a set of relations for the purpose of some discussion (typically, database normalization). Constraints that mention just one relvar are termed relvar constraints, so relation schema can be regarded as a single term encompassing a relvar and its relvar constraints.

References C.J. Date. An Introduction to Database Systems, 8th Ed. (Addison-Wesley, 2004, ISBN 0-321-19784-4), pp. 65–66. C.J. Date and Hugh Darwen. Databases, Types, and The Relational Model: The Third Manifesto (Addison-Wesley, 2007, ISBN 0-321-39942-0), p.85

Worked examples

Example 1 — a first encounter with Relvar

Start with the simplest possible case. Write down what Relvar 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 Relvar 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 Relvar 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 Relvar

In research: Relvar 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 Relvar 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: Relvar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Data modeling, Database stubs, Databases, so understanding it makes those chapters shorter.
In everyday life: Look for Relvar 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Relvar in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Relvar 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 Relvar out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Relvar in simple terms?

In relational databases, relvar is a term introduced by C. J.

Why does Relvar 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 Relvar?

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 Relvar.