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Glossary

A

Administrative Metadata

Metadata that describes the administration of a digital object. Typically, rights metadata falls within the scope of administrative metadata.

Appraisal

“Appraisal is the process of distinguishing records of continuing value from those of no further value so that the latter may be eliminated” (The National Archives (2013) What is appraisal? The National Archives).

Archive

"An organization that intends to preserve information for access and use by a Designated Community." (OAIS (2012), p.1-8, Section 1.7.2)

Aspect ratio

The ratio of the width of the frame to the height of the frame in a digital still or moving image.

Authenticity

An authentic digital object is one that can be proven to satisfy the following characteristics:

  • That it is what it purports to be.
  • That it was created or sent by the agent purported to have created or sent it.
  • That it was created or sent at the time and date it is purported to have been.

(Adapted from ISO 15489:2001)

B

Bit

A binary value of either 0 or 1 encoded into a single unit of digital information storage.

Bit Depth

Bit depth refers to the number of bits available in order to describe something. In general, the more bits that are available, the more accurate the resulting output from the data being processed. For example; the bit depth within a digital image will indicate the number of colours or brightness which are available to represent the colours or shades of grey in the original image.

Bit Rate

Bit Rate describes how quickly information can be exchanged or processed per unit of time.

Bitstream

A sequence of bytes. A bitstream may be a file or an individual element of a file. For example; a video file can be composed of a moving image component as well as an audio component. A bitstream can refer to these components in turn as well as the video file that incorporates the two components.

Bitstream Preservation

An aspect of digital preservation that seeks to ensure that a bit-perfect copy is maintained within the archive by monitoring and maintaining the integrity of each bitstream.

Byte

A unit of digital information, normally the equivalent to eight bits.

C

Characterisation

The aspect of preservation concerned with understanding the nature of digital objects, including their technical and significant properties.

Checksum

A value calculated by an algorithm based on the bit-level content of a file. Any change to that content will result in a different checksum value. Checksums can therefore be used to detect changes in the data. Integrity checks can therefore be performed based on the checksum values calculated.

Codec

The algorithm used to encode and decode raw datastream.

Collection or Study Level Metadata

Collection or study level metadata provides an overarching layer of context, provenance and inherent relationships to the individual files you may have within a particular collection or project.

Colour Resolution

See Bit Depth

Colour Sample Ratio

Within digital video, colour sample ratio refers to the ratio between the samples of luma (the brightness of an image) and the samples of chrominance, or chroma (the colour information of an image). Videos are usually encoded using some form of chroma subsampling (in order to save space) because humans' perception of brightness is usually greater than their perception of colour.

Colour Space

A colour space is a specific implementation of a colour model (which is a model of turning colours into units of measurements). A colour space allows for the reproducible representation of colours on a computer screen. Adobe RGB 1998 and sRGB are common examples.

Compression

Compression involves encoding information using fewer bits than the original representation (Mahdi, O.A.; Mohammed, M.A.; Mohamed, A.J. (November 2012). Implementing an convert audio compression to text coding via hybrid technique. International Journal of Computer Science Issues 9 (6, No. 3): 53–59).

There are two types of compression; lossy compression or lossless compression.

D

Data

"A reinterpretable representation of information in a formalized manner suitable for communication, interpretation, or processing. Examples of data include a sequence of bits, a table of numbers, the characters on a page, the recording of sounds made by a person speaking, or a moon rock specimen." (OAIS (2012), p.1-9, Section 1.7.2)

Data Rate

See Bit Rate

Descriptive Metadata

The data that is captured around the content information/meaningful content. This aids in search and retrieval.

Digital Object

"An object composed of a set of bit sequences." (OAIS (2012), p.1-10, Section 1.7.2)

An individual digital object refers to a single set of bit sequences – 1x TIFF for example.

A complex digital object refers to a digital object that relies on multiple digital objects in order to render – a webpage for example.

Digital Preservation

“[A] series of actions and interventions throughout the lifecycle to ensure continued & reliable access to authentic digital objects for as long as they are deemed valuable.” (Jisc briefing paper: Digital preservation (2006), Jisc

Directory

A logical location that allows a user to group files together. The term 'folder' is commonly used as a synonym for directory.

E

Encryption

The use of algorithms to encode data in order to prevent unauthorised systems or individuals from accessing the message.

F

Fidelity

"The degree of exactness with which something is copied or reproduced." (Oxford Dictionaries, Oxford University Press)

File

A digital object that is managed by a computer file system as a single, named entity.

File Level Metadata

File-level metadata refers to the description of individual files within a particular collection. File-level metadata may be embedded in the file itself or recorded in an associated file such as a spreadsheet or digital notebook.

Fixity

The term fixity refers to the ability to protect a digital object's integrity which, in turn, supports its authenticity. Typically this will involve using a checksum which can be monitored to ensure that no unauthorised or accidental alteration has been made.

Format

A predefined structure for organising a file.

Frame Rate

The frequency at which frames in a television picture, film, or video sequence are displayed (Oxford Dictionaries, Oxford University Press).

Frame Size

See Pixel Array

I

Integrity

The integrity of a digital object is based on proving that its medium and message are complete and unaltered. (Adapted from ISO 15489:2001)

L

Logical Preservation

An aspect of digital preservation that seeks to ensure the continued usability of digital objects, ensuring the message can be rendered and understood.

Lossless Compression

Lossless compression is a technique used produce smaller file sizes by creating a "statistical shorthand" that signifies redundant data. This is then 'packed' into a smaller file. When the file is decompressed all original data is reconstructed.

Lossy Compression

Lossy Compression removes bits by identifiying and stripping irrelevant data along with removing some redundant data also. Removing irrelevant data is based on the characteristics of human perception. Some information is more easily perceived and therefore more important than other information. This data is lost forever and returns a file at a smaller size but at the price of lower quality.

M

METS

See Metadata Encoding and Transmission Standard

Master

A file that represents an authoritative source of data.

Message

The meaningful content encoded within a digital object. The term message refers to the intellectual entity the digital object represents.

Metadata

"Data about other data." (OAIS (2012), p.1-11, Section 1.7.2)

Metadata Encoding and Transmission Standard (METS)

A metadata standard developed and maintained by the Library of Congress. The standard acts as a 'wrapper'. It allows for the incorporation of other metadata standards and encode various descriptive metadata, administrative metadata and technical metadata in a single document.

O

Optical Character Recognition

Optical Character Recognition (OCR) is a process of converting digital images containing text characters into machine-readable text.

P

Pixel Array

The number of pixels which form a digital still or moving image, usually measured by the number of pixels in the height of the image x the number of pixels in the width of the image. The term resolution is commonly used to describe a pixel array, although American, Japanese, and international digital camera standards specify that it should not be so used in this way.

Preservation Planning

An aspect of preservation that is concerned with identifying threats to the continued usability of authentic digital objects. If such threats are identified then appropriate countermeasures should be determined. It incorporates the process of technology watch.

Provenance

"The information that documents the history of the Content Information. This information tells the origin or source of the Content Information, any changes that may have taken place since it was originated, and who has had custody of it since it was originated. Examples of Provenance Information are the principal investigator who recorded the data, and the information concerning its storage, handling, and migration." (OAIS (2012), p.1-12, Section 1.7.2)

Q

Quarantine

A process that isolates the digital objects from other systems until it has been confirmed to be free from any malicious software.

R

Raster Image

Raster images are defined by pixels. Each pixel is assigned a location and a colour and plotted on a grid-like dot matrix. The spatial resolution (height x width), the bit-depth (the amount of colour information recorded per pixel), and the level of compression used all affect the resulting quality of a raster image.

Raster images are suited to continuous tone images and are produced by scanners or digital cameras.

Reliability

The reliability of a digital object is determined by its ability to demonstrate that it has trusted and dependable contents. (Adapted from ISO 15489:2001)

S

Sample Rate

Sampling refers to the quality of reproducing an analogue signal as a digital signal. A sample rate is the number of samples that are taken per second to produce a digital representation.

Significant Properties

Any intrinsic property of an information object that contributes to the assertion of its authenticity.

Spatial Resolution

Spatial resolution refers to the number of independent pixel values per unit length. This determines the clarity of the image.

T

Technical Metadata

Metadata that describes the creation, composition and other technical properties of a digital object. The significant properties of a digital object are often derived from technical metadata.

Technology Watch

The process of monitoring technological changes, in order to detect those that may affect the continued usability of a digital object.

Thumbnail

Very small representations of a digital object. They are typically used to help people quickly locate, organise and manage digital objects within their collection.

U

Usability

The usability of a digital object refers to its ability to be located, retrieved, presented and interpreted. (Adapted from ISO 15489:2001)

V

Validation

The process of confirming something data is complete, accurate and properly formed.

Vector Image

Vector images are defined by mathematical equations that represent lines, shapes and attributes. They are created by computer programs and are resolution independent, meaning that scaling does not affect the quality of the image.

Version

An iteration of a particular digital object.

W

Wrapper

The file format container that wraps one or more raw datastreams along with other data such as metadata.