An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique class of objects, where the 'object' or class may be an idea, physical [countable] object (or class thereof), or physical [noncountable] substance (or class thereof). The abbreviation ID often refers to identity, identification (the process of identifying), or an identifier (that is, an instance of identification). An identifier may be a word, number, letter, symbol, or any combination of those.
Identifiers on the back of a statue in the Louvre
The words, numbers, letters, or symbols may follow an encoding system (wherein letters, digits, words, or symbols stand for (represent) ideas or longer names) or they may simply be arbitrary. When an identifier follows an encoding system, it is often referred to as a code or ID code. For instance the ISO/IEC 11179 metadata registry standard defines a code as system of valid symbols that substitute for longer values in contrast to identifiers without symbolic meaning. Identifiers that do not follow any encoding scheme are often said to be arbitrary IDs; they are arbitrarily assigned and have no greater meaning. (Sometimes identifiers are called 'codes' even when they are actually arbitrary, whether because the speaker believes that they have deeper meaning or simply because they are speaking casually and imprecisely.)
The unique identifier (UID) is an identifier that refers to only one instanceâonly one particular object in the universe. A part number is an identifier, but it is not a unique identifierâfor that, a serial number is needed, to identify each instance of the part design. Thus the identifier 'Model T' identifies the class(model) of automobiles that Ford's Model T comprises; whereas the unique identifier 'Model T Serial Number 159,862' identifies one specific member of that classâthat is, one particular Model T car, owned by one specific person.
The concepts of name and identifier are denotatively equal, and the terms are thus denotatively synonymous; but they are not always connotatively synonymous, because code names and ID numbers are often connotatively distinguished from names in the sense of traditional natural language naming. For example, both 'Jamie Zawinski' and 'Netscape employee number 20' are identifiers for the same specific human being; but normal English-language connotation may consider 'Jamie Zawinski' a 'name' and not an 'identifier', whereas it considers 'Netscape employee number 20' an 'identifier' but not a 'name'. This is an emic indistinction rather than an etic one.
Metadata[edit]
In metadata, an identifier is a language-independent label, sign or token that uniquely identifies an object within an identification scheme. The suffix identifier is also used as a representation term when naming a data element.
ID codes may inherently carry metadata along with them. For example, when you know that the food package in front of you has the identifier '2011-09-25T15:42Z-MFR5-P02-243-45', you not only have that data, you also have the metadata that tells you that it was packaged on September 25, 2011, at 3:42pm UTC, manufactured by Licensed Vendor Number 5, at the Peoria, IL, USA plant, in Building 2, and was the 243rd package off the line in that shift, and was inspected by Inspector Number 45.
Arbitrary identifiers might lack metadata. For example, if a food package just says 100054678214, its ID may not tell anything except identityâno date, manufacturer name, production sequence rank, or inspector number. In some cases, arbitrary identifiers such as sequential serial numbers leak information (i.e. the German tank problem). Opaque identifiersâidentifiers designed to avoid leaking even that small amount of informationâinclude 'really opaque pointers' and Version 4 UUIDs.
In computer science[edit]
In computer science, identifiers (IDs) are lexicaltokens that name entities. Identifiers are used extensively in virtually all information processing systems. Identifying entities makes it possible to refer to them, which is essential for any kind of symbolic processing.
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In computer languages[edit]
In computer languages, identifiers are tokens (also called symbols) which name language entities. Some of the kinds of entities an identifier might denote include variables, types, labels, subroutines, and packages.
Which character sequences constitute identifiers depends on the lexical grammar of the language. A common rule is alphanumeric sequences, with underscore also allowed, and with the condition that it not begin with a digit (to simplify lexing by avoiding confusing with integer literals) â so
foo, foo1, foo_bar, _foo are allowed, but 1foo is not â this is the definition used in earlier versions of C and C++, Python, and many other languages. Later versions of these languages, along with many other modern languages, support almost all Unicode characters in an identifier. However, a common restriction is not to permit whitespace characters and language operators; this simplifies tokenization by making it free-form and context-free. For example, forbidding + in identifiers due to its use as a binary operation means that a+b and a + b can be tokenized the same, while if it were allowed, a+b would be an identifier, not an addition. Whitespace in identifier is particularly problematic, as if spaces are allowed in identifiers, then a clause such as if rainy day then 1 is legal, with rainy day as an identifier, but tokenizing this requires the phrasal context of being in the condition of an if clause. Some languages do allow spaces in identifiers, however, such as ALGOL 68 and some ALGOL variants â for example, the following is a valid statement: real half pi; which could be entered as .real. half pi; (keywords are represented in boldface, concretely via stropping). In ALGOL this was possible because keywords are syntactically differentiated, so there is no risk of collision or ambiguity, spaces are eliminated during the line reconstruction phase, and the source was processed via scannerless parsing, so lexing could be context-sensitive.
In most languages, some character sequences have the lexical form of an identifier but are known as keywords â for example,
if is frequently a keyword for an if clause, but lexically is of the same form as ig or foo namely a sequence of letters. This overlap can be handled in various ways: these may be forbidden from being identifiers â which simplifies tokenization and parsing â in which case they are reserved words; they may both be allowed but distinguished in other ways, such as via stropping; or keyword sequences may be allowed as identifiers and which sense is determined from context, which requires a context-sensitive lexer. Non-keywords may also be reserved words (forbidden as identifiers), particularly for forward compatibility, in case a word may become a keyword in future. In a few languages, e.g., PL/1, the distinction is not clear.
The scope, or accessibility within a program of an identifier can be either local or global. A global identifier is declared outside of functions and is available throughout the program. A local identifier is declared within a specific function and only available within that function.[1]
For implementations of programming languages that are using a compiler, identifiers are often only compile time entities. That is, at runtime the compiled program contains references to memory addresses and offsets rather than the textual identifier tokens (these memory addresses, or offsets, having been assigned by the compiler to each identifier).
In languages that support reflection, such as interactive evaluation of source code (using an interpreter or an incremental compiler), identifiers are also runtime entities, sometimes even as first-class objects that can be freely manipulated and evaluated. In Lisp, these are called symbols.
Compilers and interpreters do not usually assign any semantic meaning to an identifier based on the actual character sequence used. However, there are exceptions.
For example:
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In some languages such as Go, identifiers uniqueness is based on their spelling and their visibility.[2]
In HTML an identifier is one of the possible attributes of an HTML element. It is unique within the document.
Ambiguity[edit]Identifiers (IDs) versus Unique identifiers (UIDs)[edit]
Many resources may carry multiple identifiers. Typical examples are:
The inverse is also possible, where multiple resources are represented with the same identifier (discussed below).
Implicit context and namespace conflicts[edit]
Many codes and nomenclatural systems originate within a small namespace. Over the years, some of them bleed into larger namespaces (as people interact in ways they formerly hadn't, e.g., cross-border trade, scientific collaboration, military alliance, and general cultural interconnection or assimilation). When such dissemination happens, the limitations of the original naming convention, which had formerly been latent and moot, become painfully apparent, often necessitating retronymy, synonymity, translation/transcoding, and so on. Such limitations generally accompany the shift away from the original context to the broader one. Typically the system shows implicit context (context was formerly assumed, and narrow), lack of capacity (e.g., low number of possible IDs, reflecting the outmoded narrow context), lack of extensibility (no features defined and reserved against future needs), and lack of specificity and disambiguating capability (related to the context shift, where longstanding uniqueness encounters novel nonuniqueness). Within computer science, this problem is called naming collision. The story of the origination and expansion of the CODEN system provides a good case example in a recent-decades, technical-nomenclature context. The capitalization variations seen with specific designators reveals an instance of this problem occurring in natural languages, where the proper noun/common noun distinction (and its complications) must be dealt with. A universe in which every object had a UID would not need any namespaces, which is to say that it would constitute one gigantic namespace; but human minds could never keep track of, or semantically interrelate, so many UIDs.
Identifiers in various disciplines[edit]
See also[edit]
References[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Identifier&oldid=898054280'
A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. Other things have serial numbers as well, though, including banknotes and other similar documents.
The idea behind serial numbers is to identify a specific item, much like how a fingerprint identifies a specific person. Instead of some names or numbers that specify a whole range of products, a serial number is intended to provide a unique number to one device at a time.
Hardware serial numbers are embedded in the device, while software or virtual serial numbers are sometimes applied to the user who will be using the software. In other words, a serial number used for software programs are tied to the purchaser, not that specific copy of the program.
The term serial number is often shortened to just S/N or SN, especially when the word precedes an actual serial number on something. Serial numbers are also sometimes, but not often, referred to as serial codes.
Serial Numbers Are Unique
It's important to distinguish serial numbers from other identifying codes or numbers. In short, serial numbers are unique.
For example, a model number for a router might be EA2700 but that's true for every single Linksys EA2700 router; the model numbers are identical while each of their serial numbers is unique to each particular component.
As an example, if Linksys sold 100 EA2700 routers in one day from their website, every one of those devices would have 'EA2700' somewhere on them and they would look identical to the naked eye. However, each device, when first built, had serial numbers printed on most of the components that are not the same as the others bought that day (or any day).
UPC Codes are common as well but are actually not unique like serial numbers. UPC Codes are different than serial numbers because UPC Codes are not unique to each individual piece of hardware or software, as serial numbers are.
The ISSN used for magazines and ISBN for books is different as well because they're used for whole issues or periodicals and aren't unique for every instance of the copy.
Hardware Serial Numbers
You've probably seen serial numbers many times before. Nearly every piece of the computer has a serial number including your monitor, keyboard, mouse and sometimes even your entire computer system as a whole. Internal computer components like hard drives, optical drives, and motherboards also feature serial numbers.
Idm Serial Number
Serial numbers are used by hardware manufacturers to track individual items, usually for quality control.
For example, if a piece of hardware is recalled for some reason, customers are usually made aware of which particular devices need service by being provided a range of serial numbers.
Serial numbers are also used in non-tech environments like when keeping an inventory of tools borrowed in a lab or shop floor. It's easy to identify which devices need to be returned or which ones have been misplaced because each of them can be identified by their unique serial number.
Software Serial Numbers
Serial numbers for software programs are usually used to help ensure that the program's installation is only performed one time and only on the purchaser's computer. New south movie 2018. Once the serial number is used and registered with the manufacturer, any future attempt to use that same serial number can raise a red flag since no two serial numbers (from the same software) are alike.
If you're planning on reinstalling a software program you've purchased, you'll sometimes need the serial number to do so. See our guide on how to find a serial key if you need to reinstall some software.
Serial Number Check
Sometimes, you might find that a software program can attempt to make a serial number for you that you can use to activate a program illegally (since the code wasn't legally purchased). These programs are called keygens (key generators) and should be avoided.
![]() Internet Download Manager Serial Number
A serial number for a piece of software is not usually the same as a product key but they are sometimes used interchangeably.
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