computer science

Object Query Language

Object Query Language 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 Object Query Language rather than just read about it. In short: Object Query Language (OQL) is a query language standard for object-oriented databases modeled after SQL and developed by the Object Data Management Group (ODMG). Because of its overall complexity the complete OQL standard has not yet been fully implemented in any software.

Key takeaways

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

Reference excerpt

Object Query Language (OQL) is a query language standard for object-oriented databases modeled after SQL and developed by the Object Data Management Group (ODMG). Because of its overall complexity the complete OQL standard has not yet been fully implemented in any software. The OQL standard influenced the design of later query languages such as JDOQL and EJB QL, though none are considered to be any version of OQL.

General rules The following rules apply to OQL statements:

All complete statements must be terminated by a semi-colon. A list of entries in OQL is usually separated by commas but not terminated by a comma. Strings of text are enclosed by matching quotation marks.

Examples

Simple query The following example illustrates how one might retrieve the CPU-speed of all PCs with more than 64MB of RAM from a fictional PC database:

Query with grouping and aggregation The following example illustrates how one might retrieve the average amount of RAM on a PC, grouped by manufacturer:

Note the use of the keyword partition, as opposed to aggregation in traditional SQL.

See also Object Data Management Group (ODMG) Object Definition Language

References

Worked examples

Example 1 — a first encounter with Object Query Language

Start with the simplest possible case. Write down what Object Query Language 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 Object Query Language 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 Object Query Language 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 Object Query Language

In research: Object Query Language 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 Object Query Language 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: Object Query Language is common in secondary-school and first-year university syllabi. It links to neighbouring topics Programming language topic stubs, Query languages, Software engineering stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Object Query Language 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 Object Query Language in 20 minutes

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

Frequently asked questions

What is Object Query Language in simple terms?

Why does Object Query Language 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 Object Query Language?

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 Object Query Language.