chemistry

Molecular Query Language

Molecular Query Language is a chemistry 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 Molecular Query Language rather than just read about it. In short: The Molecular Query Language (MQL) was designed to allow more complex, problem-specific search methods in chemoinformatics. In contrast to the widely used SMARTS queries, MQL provides for the specification of spatial and physicochemical properties of atoms and bonds.

Key takeaways

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

Reference excerpt

The Molecular Query Language (MQL) was designed to allow more complex, problem-specific search methods in chemoinformatics. In contrast to the widely used SMARTS queries, MQL provides for the specification of spatial and physicochemical properties of atoms and bonds. Additionally, it can easily be extended to handle non-atom-based graphs, also known as "reduced feature" graphs. The query language is based on an extended Backus–Naur form (EBNF) using JavaCC.

Notes and references E. Proschak, J. K. Wegner, A. Schüller, G. Schneider, U. Fechner, Molecular Query Language (MQL)-A Context-Free Grammar for Substructure Matching, J. Chem. Inf. Model., 2007, 47, 295–301. doi:10.1021/ci600305h

See also SMARTS International Chemical Identifier

External links Java Webstart application for MQL

Worked examples

Example 1 — a first encounter with Molecular Query Language

Start with the simplest possible case. Write down what Molecular Query Language claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Molecular 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 Molecular 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 Molecular Query Language

In research: Molecular Query Language appears in chemistry 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 Molecular 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: Molecular Query Language is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cheminformatics, so understanding it makes those chapters shorter.
In everyday life: Look for Molecular 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 Molecular Query Language in 20 minutes

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

Frequently asked questions

What is Molecular Query Language in simple terms?

Why does Molecular Query Language matter?

Because it connects several chemistry 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 Molecular 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 Molecular Query Language.