computer science

Low-level design

Low-level design 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 Low-level design rather than just read about it. In short: Low-level design (LLD) is a component-level design process that follows a step-by-step refinement process. This process can be used for designing data structures, required software architecture, source code and ultimately, performance algorithms.

Key takeaways

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

Reference excerpt

Low-level design (LLD) is a component-level design process that follows a step-by-step refinement process. This process can be used for designing data structures, required software architecture, source code and ultimately, performance algorithms. Overall, the data organization may be defined during requirement analysis and then refined during data design work. Post-build, each component is specified in detail. The LLD phase is the stage where the actual software components are designed. During the detailed phase the logical and functional design is done and the design of application structure is developed during the high-level design phase.

Design phase A design is the order of a system that connects individual components. Often, it can interact with other systems. Design is important to achieve high reliability, low cost, and good maintain-ability. We can distinguish two types of program design phases:

Architectural or high-level design Detailed or low-level design Structured flow charts and HIPO diagrams typify the class of software design tools and these provide a high-level overview of a program. The advantages of such a design tool are that it yields a design specification understandable to non-programmers and provides a good pictorial display of the module dependencies. A disadvantage is that it may be difficult for software developers to go from a graphic-oriented representation of software design to implementation. Therefore, it is necessary to provide little insight into the algorithmic structure describing procedural steps to facilitate the early stages of software development, generally using Program Design Languages (PDLs).

Purpose The goal of LLD or a low-level design document (LLDD) is to give the internal logical design of the actual program code. Low-level design is created based on the high-level design. LLD describes the class diagrams with the methods and relations between classes and program specs. It describes the modules so that the programmer can directly code the program from the document. A good low-level design document makes the program easy to develop when proper analysis is utilized to create a low-level design document. The code can then be developed directly from the low-level design document with minimal debugging and testing. Other advantages include lower cost and easier maintenance.

References

Worked examples

Example 1 — a first encounter with Low-level design

Start with the simplest possible case. Write down what Low-level design 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 Low-level design 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 Low-level design 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 Low-level design

In research: Low-level design 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 Low-level design 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: Low-level design is common in secondary-school and first-year university syllabi. It links to neighbouring topics Design, Software design, so understanding it makes those chapters shorter.
In everyday life: Look for Low-level design 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 Low-level design in 20 minutes

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

Frequently asked questions

What is Low-level design in simple terms?

Why does Low-level design 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 Low-level design?

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 Low-level design.