Glossary

Term	Definition	Alternative Title(s)	See also
Application	A software utility that has been created to perform specific tasks for an end user. An application typically provides an interface for a user to interact with. Examples include word processors, image viewers and manipulation software, video renders, video games etc.
ASCII	Acronym for American Standard Code for Information Interchange, a legacy character encoding that was adopted by most of the western computing industry. ASCII encodes control characters and printable characters consistently promoting the exchange of information between computers, and other electronic mediums.
Binary	Data stored in binary encoding—that is, as sequences of bytes rather than human-readable text. These bytes represent values, instructions, or structured data that are interpreted by software according to the format’s specification.
Binary Signature	The definition of an identification pattern used by file format identification tools. A Binary Signature can have 1 or more Binary Signature Patterns, and all patterns for a given signature must match to return a hit and receive positive identification. A PRONOM file format entry can have 0 or more Binary Signatures, and if any of these signiatures match they will return a hit and receive positive identification.
Binary Signature File	A file used by the file format identification tool, that stores all of its Binary Signature definitions and their associations with PRONOM file format entries.
Binary Signature Pattern	A single pattern, associated with any one of the BOF, EOF, or Variable positions within a file, that must be present to return a hit. A Binary Signature can have 1 or more Binary Signature Patterns, and all patterns for a given signature must match to return a hit and receive positive identification.
Bit	A unit of digital information representing
BOF	An acronym that describes the Beginning of File. BOF is used to describe an offset from the beginning of file for a PRONOM signature or magic number.		Offset, EOF, VAR
Byte	A unit of digital information representing 8 bits of data. A single byte may have one of 256 possible values, that can be simply expressed using a Hexadecimal pair.		Bit
Bytecode	The raw, unprocessed data within a file as stored. A Hex Editor will display the Bytecode of a file instance without attempting to process or interpret it.
Byte-order	Byte order, or endianness, is a computer system’s convention for how multi-byte data like integers are stored in computer memory or transmitted over a network. The two main types are big-endian, which places the most significant byte first, and little-endian, which places the least significant byte first.
Character Sets	A defined collection of characters, i.e. letters, numbers, symbols and control codes, that a computer can store, display, and manipulate. Popular character sets include ASCII (American Standard Code for Information Interchange), a simple character set covering English letters, digits and punctuation, Unicode (e.g. UTF-8, UTF-16), an extended character set covering virtually all written languages, symbols and emojis, ANSI (American National Standards Institute) refers to a family of extended character sets that have different character mappings, or ‘Code Pages’ for different regions, e.g. Windows-1252 covers western European languages. Windows-1251 covers Cyrillic languages
Characters	A byte or set of bytes that compose a printable character, for example the letter ‘A’. Characacters combine to make a string (a string of bytes).		Bytes
Classification	A type definition given to a file format in the PRONOM database that describes the overall content of the file, e.g. video, structured text, image, and so on.	File format classification
Container	A file format that allows multiple data streams to be embedded into a single file, often inside a ZIP or OLE archive.
Container Signature	An alternative definition of an identification pattern used by file format identification tools, used when files are themselves Containers, based on ZIP or OLE, that under-the-hood contain multiple files that could be individually interrogated and processed. A Container Signature can have 1 or more Container Signature Patterns, and all patterns for a given signature must match to return a hit and receive positive identification. A PRONOM file format entry can have 0 or more Container Signatures, and if any of these signiatures match they will return a hit and receive positive identification. Usually a PRONOM format entry will only be associated with Binary Signatures, OR Container Signatures (i.e. not both), however some older PRONOM format entries are still associated with both. A Container Signature has two additional elements beyond a Binary Signature: 1) A Container Type (currently either ZIP or OLE) that means that if a file format identification tool encounters a matching Binary Signature pattern for the Container Type then the Container Signature File will be assessed for matches. 2) A Path, which is a filepath internal to the container that must be present for a hit to occur. A Path may also be associated with additional Signature Patterns associated with the BOF, EOF, or Variably within the subfile referenced by the Path, that must all match for a hit to occur. In the absence of any Signature Patterns being defined for a given Path, the existence of the Path is enough to return a hit.
Container Signature File	A file used by the file format identification tool, that stores all of its Container Signature definitions and their associations with PRONOM file format entries.
Container Type	The file format that a Binary Signature must first match before the Container Signature File is assessed for further matches. Currently the two Container Types are OLE (fmt/111), and ZIP (either x-fmt/263 or fmt/189, which is a ZIP file that precisely conforms to the Microsoft OOXML standard)
Control Character	A special byte value that may be interpreted as a computer as an instruction to perform a specific action, rather than to interpret the byte value as an alphanumeric character.
Data structure	A particular way of organizing, managing, and storing data in a computer so that it can be efficiently accessed and modified.
Decimal	The system of numbers most of us use throughout our day-to-day lives, where each digit has a range from 0-9. This system is also known as Base 10.
Digital Forensics	A branch of forensic science focused on recovering, preserving, and analyzing digital data from computers, mobile devices, and other electronic media.
DROID	A file format identification tool developed by The National Archives that uses PRONOM signatures.
Encodings	A method of converting data into a particular form, especially for representing characters in digital files (e.g., UTF-8, ASCII).
EOF	A position marker indicating the end of a file, also used in PRONOM signatures.		Offset
Extension	A suffix of a filename, separated by a period, that indicates to the Operating System, the file’s type and format.
External Signature	An externally visible mechanism for identifying a file, specifically the file format extension, which can be used to assume the file format of a given file instance, however this is easily changed and may not be unique to a given software application.
FDD	The Library of Congress ‘Format Description Document’ reference. This is a file format registry hosted by Library of Congress that typically describes file formats in much more detail than is usually found within PRONOM.
FIDO	A file format identification tool developed by the Open Preservation Foundation that also uses PRONOM data	Format Identification for Digital Objects
File	An object in computed storage that contains data.
File Format	A standardized way of storing data within a file, defining how the data is structured and stored as such that it can be interpreted and processed by a software application
File format specification	A formal definition of a file format’s structure. If a full file format specification is published openly, then this allows 3rd party software vendors to create their own implementations of software that can interpret and process a given file format.	Specification; Standard
FileFormatMapping	The internal relationship between a PRONOM entry and a File Format Signature
Footer	A defined section within a file format that typically includes data that will give information to a processing software application. This is not as common as a Header. In some cases, certain software vendors have unofficially extended formal file format definitions, by adding their own data to the end of a given file.
Format identification	The process of identifying a file’s file format from certain external (i.e. file extension), or internal (i.e. file format signatures) characteristics
Header	A defined section within a file format that typically includes data that will give information to a processing software application. This may include a Magic Number for rapid format identification, defined peoperties of the file, and much more. Some file formats do not have defined Headers
Hexadecimal	A base-16 number system (0–9 and A–F) used to represent binary data in a more human-readable format.	Hex	Byte/s
Hex Editor	A software tool that displays a file’s internal byte-code in a simplified form based on Hexadecimal notation. As an ‘editor’ it also allows files to be easily edited, so handle with care!
Identification	The process of determining a file instance’s file format based on external or internal characteristics.
InternalSignature	An internal mechanism for identifying a file based upon byte matching patterns within a given file’s bytecode.
JHOVE	An open source, extensible software framework for identification, validation, and characterisation.
Magic	A distinctive sequence of bytes at a specific location in a file that uniquely identifies the file format.	Magic number
Magic number	A unique byte sequence usually near the beginning of a file that is unique to its format (e.g., FF D8 for JPEG).
Max-byte scan	A setting which allows you to configure how far from the beginning or end of the file DROID will scan to match a signature pattern. before it stops trying to identify the file.
Metadata	Data about an asset, such as key technical characteristics. For digital information metadata may be found embedded within a given file, may be found within a separate ‘sidecar’ file, or may be found as a property stored by the software platform or operating system.
MIMEInfo	A string that identifies the format of a file to a browser or email client, telling it how to display or process the content
Multipart	A digital asset that consists of multiple files. e.g. a single rendered web page may consist of an HTML document, separate CSS and JavaScript files, separate images etc.	Multi-file
Offset	The position (in bytes) from the start or end of a file where a signature sequence begins.
Partial entry	A PRONOM entry that may contain some information, perhaps even an identification signature, but is missing key information such as a description.
Pattern matching	The process of checking that a sequence of data matches a defined pattern.
Patterns	A pattern defines the expected structure or form that data should follow, that we can use to create file format signatures
PDF	Portable Document Format, a popular file format originally created by Adobe but now maintained as an ISO Standard, that was originally intended as a format for document interchange, particularly for the printing industry.
Preservation	The set of processes and actions aimed at maintaining and protecting records and artifacts (physical or digital) to ensure their continued accessibility, usablilty, integrity, and authenticity over time.
Priority	The expression that one file format should be considered as more specific than another, therefore if a file contains more that one matching File Format Signature, then the higher priority format must take precedence. This is most commonly used when a given file format is explicitly based on another, e.g. SVG is an XML file containing elements specific to SVG, therefore SVG has priority over XML.
PRONOM	A central registry of file format signatures maintained by The UK National Archives. Used for digital preservation and file format identification.
PUID	A unique identifier assigned by the PRONOM registry associated with a specific file format	PRONOM unique identifier
Regex	A regular expression is a sequence of characters that defines a search pattern for matching strings.	Regular expression	PRONOM regex; Pattern matching
Reverse-engineering	An approach to understanding the internal structure of a given file without reference to the formal file format specification, typically based on experimentation and inference, possibly utilizing specilaized tools.
Sample	An example file instance of a given file format. It is usually beneficial to have several sample files available, ideally from diverse sources, before attempting to determine potential byte sequences for file format identification.
Sequence	A specific pattern of bytes or potential byte values as described using PRONOM syntax
Siegfried	Another file format identification tool that uses PRONOM signatures and supports custom signature files.
Signature	A specific sequence of bytes used to identify a file format. Often found at the beginning (BOF) or end (EOF) of a file.
Signature development utility	A tool, created by Ross Spencer, that enables the generation of File Format Signature Files that can then be used by a file format identification tool for testing a potential File format Signature
Skeleton	A synthetic, artificially created file that contains only the minimal data required for a file to hit a match against a give file format signature. Since these files do not contain ‘real’ data, they will typically cause error messages to be thrown if attempting to open them in the file format’s associated software application
Specification	A formal document that defines the structure and encoding rules of a file format.
Syntax	The formal set of rules that determine how code, commands, or data must be written so a computer can understand and process them correctly. PRONOM syntax is a specific language for expressing file format identification patterns, that file format identification software applications such as DROID and Seigfried have been programmed to be able to process.
Trigger	A Container Type that will result in the Container Signature File being assessed for a further match, based on the subfiles found within the Containing file format.	Trigger PUID; ContainerType
Versions	A specific form or release of a given object, concept, or software that may change over time. In the context of a PRONOM entry, the version is intended to refer to the version of a file format rather than its associated software, however in practice a given file format version is often explicitly tied either to a specific software application version or range of versions, so the distinction is not often easy to determine or to cleanly define.
Wildcard	A placeholder in a signature that can match any byte or range of bytes.
XML	eXtensible Markup Language, a popular file format created and maintained by the W3C Consortium, intended as a both human-, and machine-readable format for representing structured data