Unique identifier

Key takeaways

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

Reference excerpt

A unique identifier (UID) is an identifier that is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. The concept was formalized early in the development of computer science and information systems. In general, it was associated with an atomic data type. In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys. In mathematics, set theory uses the concept of element indices as unique identifiers.

Classification There are some main types of unique identifiers, each corresponding to a different generation strategy:

serial numbers, assigned incrementally or sequentially, by a central authority or accepted reference. random numbers, selected from a number space much larger than the maximum (or expected) number of objects to be identified. Although not really unique, some identifiers of this type may be appropriate for identifying objects in many practical applications and are, with informal use of language, still referred to as "unique" Hash functions: based on the content of the identified object, ensuring that equivalent objects use the same UID. Random number generator: based on random process. names or codes allocated by choice which are forced to be unique by keeping a central registry such as the EPC Information Services. names or codes allocated using a regime involving multiple (concurrent) issuers of unique identifiers that are each assigned mutually exclusive partitions of a global address space such that the unique identifiers assigned by each issuer in each exclusive address space partition are guaranteed to be globally unique. Examples include (1) the media access control address MAC address uniquely assigned to each individual hardware network interface device produced by the manufacturer of the devices, (2) consumer product bar codes assigned to products using identifiers assigned by manufacturers that participate in GS1 identification standards, and (3) the unique and persistent Legal Entity Identifier assigned to a legal entity by one of the LEI registrars in the Global Legal Entity Identifier System (GLEIS) managed by the Global LEI Foundation (GLEIF). The above methods can be combined, hierarchically or singly, to create other generation schemes which guarantee uniqueness. In many cases, a single object may have more than one unique identifier, each of which identifies it for a different purpose.

Examples Electronic Identifier Serial Publication (EISP) Electronic Product Code (EPC) International eBook Identifier Number (IEIN) International Standard Book Number (ISBN) National identification number Amazon Standard Identification number Part number Radio call signs Stock keeping unit (SKU) Track and trace

National identification number

National identification number is used by the governments of many countries as a means of tracking their citizens, permanent residents, and temporary residents for the purposes of work, taxation, government benefits, health care, and other governance-related functions.

Chemistry CAS registry number IUPAC nomenclature

Computing Cryptographic hashes Identity correlation MAC address Object identifier (OID) Organizationally unique identifier (OUI) Universally unique identifier (UUID) or globally unique identifier (GUID) World Wide Port Name

Economics, tax and regulation Harmonized System Payment card number Unique Transaction Identifier (UTI) Universal Product Code

Internet architecture and standards Best Current Practice (BCP) For Your Information (FYI) Internet Draft (I-D) Internet Experiment Note (IEN) Internet Standard (STD) Request for Comments (RFC) RARE Technical Reports (RTR)

Legal Bates numbering European Case Law Identifier (ECLI) Gun serial number Legal Entity Identifier (LEI) Lex (URN)

Mathematical publications Mathematical Reviews number Zentralblatt MATH identifier

Research / Science Archival Resource Keys (ARK), with 8.2 billion ARKs issued. Digital object identifiers (DOI), with 200 million DOIs issued. Identifiers.org ORCID (Open Researcher and Contributor ID) Smithsonian trinomial Systematic name

Transportation American rail transportation Reporting marks IMO number to identify sea-going ships International Air Transport Association airport codes IMO container codes according to ISO 6346 for shipping containers License plate number Maritime Mobile Service Identity (MMSI) UIC wagon numbers

Worked examples

Example 1 — a first encounter with Unique identifier

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

In research: Unique identifier appears in 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 Unique identifier 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: Unique identifier is common in secondary-school and first-year university syllabi. It links to neighbouring topics Names, Unique identifiers, so understanding it makes those chapters shorter.
In everyday life: Look for Unique identifier 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.

How to study Unique identifier in 20 minutes

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

Frequently asked questions

What is Unique identifier in simple terms?

A unique identifier (UID) is an identifier that is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. The concept was formalized early in the development of computer science and information systems.

Why does Unique identifier matter?

Because it connects several 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 Unique identifier?

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 Unique identifier.