The Digital Image Defined
The Image
Networks, System Architecture, and Storeage
Why Digitize
Project Planning
Selecting Scanners
Image Capture
Selecting a Metadata Schema
Quality Control
Security Policies & Procedures
Long-Term Management & Preservation
Online Resources
Illustration Credits
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Introduction to Art Image Access



Note: Boldface terms within entries are also defined in the glossary. In some cases, separate terms (e.g., RGB and color model) that are grouped consecutively (RGB color model) in the main text and glossary may appear to be one term.

AAT (Art & Architecture Thesaurus)
A controlled vocabulary maintained by the Getty Research Institute that identifies and organizes art and architecture terminology.

access file (or access image)
A file derived from a master file that is used to make a digital collection item accessible without hazarding the master. Typically compressed to reduce storage requirements and speed online delivery.

access points
A database field or metadata category designed to be searchable and retrievable by an end-user. Also used to denote a place where wireless network access is available.

ACL (Access Control List)
A way to limit access to networks to authorized users by using a router to forward or block requests from users based on a given protocol or criteria, such as IP address.

adaptive palette
A reduced palette of colors chosen to give the best possible reproduction of an image when it is displayed in a limited or "palettized" color environment, such as an 8-bit (256-color) display, or within a 256-color image format, such as GIF.

AFRICOM (International Council of African Museums)
Body that originated as a program of the International Council of Museums (ICOM) that has developed a metadata standard designed to promote the standardization of museum collection inventories in Africa.

A set of steps in a specific order, such as the instructions in a computer program. Different image compression schemes employ different algorithms; for instance, the JPEG algorithm processes images as 8 x 8 image-blocks and applies cosine transformations to each block, while the JPEG2000 algorithm applies wavelet transformations to the image as a whole.

Any continually fluctuating or changing process, or any mechanism in which data is represented by continuously variable quantities. Analog images are continuous tone-the range of colors or shades of gray that they can include are virtually unlimited, and therefore their colors graduate smoothly. Because data in analog form can theoretically be represented by an infinite number of values, it may be difficult to differentiate between accurate reproduction and noise; thus, analog technology does not facilitate the accurate creation of copies, and analog reproduction may be of lower quality than digital reproduction.

Commentary added to a media object, generally providing explanatory information or editorial notes regarding the media file. Annotations are a form of metadata.

ANSI (American National Standards Institute)
U.S.-based body that does not directly develop standards but coordinates and administers voluntary consensus standardization initiatives.

archival master
The raw, original image captured by the scanning process and/or an image created and managed so as to optimize longevity and future usefulness. File naming, file formatting, color space selection, capture resolution, and similar specifications should be based on documented standards. Archival masters may be used as the source for access images, or these may be created from derivative masters. See digital preservation.

An error introduced into an image during capture or digitization, formatting, compression, or other transformation processes. Most commonly used to refer to the perceptible degradation of an image after a lossy compression schema has been used.

ASP (Active Server PageT)
One of several methods of dynamically generating Web pages in response to user input that may be used to gather information from remote databases. Utilizes "ActiveX" scripts. A Microsoft specification that may require third-party software to run on non-Windows platforms. ASP may also indicate an Application Service Provider. See CGI, JSP, PHP.

A human or machine process that verifies that an individual, computer, or information object is who or what s/he or it purports to be. Used in allowing access to secure systems.

Refers to the trustworthiness of a digital entity, to its being what it professes to be, as regards its identity, origin, history, authorship, integrity, and/or the accuracy with which it documents an original work. The degree to which authenticity can be ascertained or guaranteed is likely to be determined by the quality of custody or management an entity enjoys over its life cycle.

authority (or authority file)
A file or set of terms extrinsic to records describing objects or documents. A more efficient way of recording information, which need be recorded only once and may then be linked to all appropriate records.

Denotes the capacity of a communications channel, such as an Internet link. Determines how fast data can flow over the channel. See bit rate.

batch processing
The automated application of a given process, such as compression, to multiple files.

The smallest unit of computer data, denoted by a single binary value, either 0 or 1. Eight bits make up one byte in most computer systems.

bit depth
Also known as sample depth or color depth. The number of bits used to describe the color value of each pixel in an image, which in turn dictates the number of colors available to a given media file, monitor, or other device. An 8-bit image has 256 possible colors. A 24-bit image has approximately 16 million. See dynamic range.

bitmap (or bitmapped image, raster image)
An image made up of a given number of pixels, each with a specific color value, laid out in a grid. Ideal for reproducing photographic representations, because a sufficient quality and quantity of pixels can give the appearance of a continuous tone image. Resizing will affect apparent image quality. For instance, enlarging an image involves enlarging each pixel, which entails a reduction in resolution. See vector graphic.

bit rate
The number of bits that pass a given point in a network in a given amount of time, generally measured in kilobits or megabits per second (Kbps or Mbps). The bit rate is a measure of bandwidth and may also be referred to as the data transfer rate.

A system of logical thought developed by George Boole (1815-1864) and adopted for use with binary values of computer operations. In Boolean searching, terms such as AND, OR, and NOT are used as operators to combine or exclude search terms.

born digital
Creations originally generated in digital form rather than copies or surrogates of analog originals, and which exist entirely in a digital environment. Examples include software, Web pages, hypertext fiction, and digital art.

High-speed data transmission or a transmission medium in which a wide range or band of frequencies is available to transmit data, allowing more information to be transmitted in a given time frame. As of this writing, broadband is sometimes defined as services that offer bit rates of 1.544 megabits per second (Mbps) and above. May also be referred to as wideband. Digital Subscriber Lines (DSLs) and cable modems allow broadband transmission. See bandwidth.

See Web browser.

browser-safe palette
A palette of 216 colors whose appearance is predictable in all browsers and operating systems. Developed for 256-color displays-the remaining 40 colors are rendered differently by Macintosh and IBM-compatible or Wintel operating systems. Still used in Web design.

BSI (British Standards Institution)

Body that coordinates and publishes British, European, and international best practice recommendations and standards.


In most computer systems, a unit of data that is eight binary digits or bits long. Generally used to represent a character such as a letter or number but may also hold a string of bits needed in some larger unit, such as the stream of bits that make up a visual image.

CAD (Computer-Aided Design)
Software used in architecture, archaeology, design, and other fields to create precision drawings, models, and technical illustrations in two or three dimensions. See born digital, vector graphic.

The comparison of the specifications of image-capture, processing, or display devices to a known standard to determine, and perhaps correct, any deviation or error. See color management.

capture resolution
The number of samples per inch (spi) that a scanner or digital camera is capable of capturing, or the number of samples per inch captured when a particular image is digitized.

The process of creating and arranging records that describe materials so as to facilitate identification, search and retrieval, acquisitions, circulation, preservation, rights, evaluation, and collocation. A record generally consists of a description; headings for topics, persons, places, etc.; an identification number; and links to related resources, such as authority records. Differs from a simple listing by the imposition of controlled vocabularies and by mechanisms allowing users to draw relationships between various entities.

CBIR (Content-Based Information Retrieval)
Technology that is able to retrieve images on the basis of machine-recognizable visual criteria. Such indexing is able to recognize and retrieve images by criteria such as color, iconic shape, or by the position of elements within the image frame.

CCD (Charge-Coupled Device)
Light-sensitive integrated circuits employed in image capture by scanners and digital cameras. CCDs capture image data as pixels with a numerical value that can be converted into an electrical charge, the intensity of which is related to a particular color.

The former Comité Consultatif Internationale de Télégraphique et Téléphonique, now the ITU, that develops communications standards, including a group of related lossless compression schemas for black-and-white images used in fax transmission and supported by the PDF and PostScript language file formats.

CD-ROM (Compact Disk, Read-Only Memory)
A type of write-once, read-many (WORM) disk used to store and distribute large amounts of digital data on low-cost, optically recorded media. CD-ROMs profess to have much longer storage life ratings than magnetic media such as tape or hard disks, though there have been a few notable instances of failure in less than five years. Gold-reflective-layer CDs are most recommended for long-term storage. A standard CD-ROM stores approximately 650 megabytes of data. See DVD-ROM.

CDWA (Categories for the Description of Works of Art)
A conceptual framework for describing and accessing information about artworks and surrogates, maintained by the Getty Research Institute. The Visual Resources Association (VRA) Data Standards Committee expanded upon certain portions of the CDWA to formulate the VRA Core Categories.

CGI (Common Gateway Interface)
Part of the Web's Hypertext Transfer Protocol (HTTP). A platform- independent method of dynamically generating Web pages in response to user input that may be used to gather information from remote databases. See ASP, JSP, PHP.

The separate color components used by various color models. By default, RGB images have three channels: red, green, and blue; CMYK images have four: cyan, magenta, yellow, and black. Extra or "alpha" channels can be added to describe, for example, levels of transparency, or be used as masks that allow or restrict the output of color. Color creation occurs when the channels are combined before being sent to an output device such as a screen or printer.

A simple count of the total number of bits in a file or transmission unit that may be used to assess data integrity or detect error. In digital preservation management, checksums can be used to ascertain whether the number of bits in a file has changed over time.

CIDOC (International Committee for Documentation)
A committee of the International Council of Museums (ICOM) involved in developing documentation standards, such as the CIDOC Information Categories and CRM. See AFRICOM.

CIDOC Information Categories
A metadata standard intended to describe museum collection objects developed by the International Committee for Documentation.

CIE (Commission Internationale de l'Eclairage)
Organization that has developed a number of device-independent color models collectively called CIE color, including CIE XYZ, CIE LAB, and CIE LUV, that specify color based on human perception and are used as the basis for color management systems. See CMS, color profile.

See client/server.

Refers to a system architecture that divides functions between two or more computers, or two or more programs, so that one program, the client, makes a service request from another program, the server, which fulfills the request. This architecture is seen in networks where a client program in one computer (such as a Web browser) forwards a request to a server program in another (possibly distantly located) computer, which returns information to the client.

CMS (Color Management System)
A system designed to ensure the most accurate reproduction of color across multiple input, output, and display devices, and through the life cycle of an image. Each device in a color workflow will have inherent biases that cause it to interpret digital color values differently, and no device can properly reproduce the entire range of visible colors. Modern color management systems employ ICC color profiles to describe the color reproduction capabilities (and limitations) of individual devices. These are mapped to a device-independent CIE-based color space, facilitating conversion to matching color output across multiple devices and systems, within the practical limits of the devices. CMS may also refer to Content or Collection Management Systems.

CMYK (Cyan, Magenta, Yellow, Black)
Often referred to as four-color process, CMYK is a subtractive color model, using a mix of cyan, magenta, yellow, and black inks to reproduce a range of colors. CMYK is the most basic color process used in print.

A compression/decompression (sometimes coder/decoder) algorithm or scheme that reduces the volume of bits necessary to store a data object such as an image file (compression) but that allows the reconstruction of the compressed data into a usable format for display, processing, etc. (decompression). There are many different codecs, and they are often used to minimize file transfer time in order to optimize images or data for Web use.

color chart
A calibration target consisting of a matrix or spectrum of colors set to a known standard. Color charts can provide reference points to ensure accuracy of color capture and to calibrate output devices. May also be referred to as a color patch. See gray scale.

color correction
The process of adjusting color values in an image to match the original or a reference image in order to compensate for the normal shifts and biases incurred during digitization and subsequent image processing. See CMS.

color depth
See bit depth.

color management
The practice of calibrating all devices in the image capture, processing, and output chain to ensure the fidelity of digital image files to the objects they represent. Color management can be achieved by manually calibrating devices using color charts and ICC profiles followed by regular reassessment, or by means of CMS software.

color model
An attempt to describe color in a mathematical, predictable, and reproducible way. Usually posits a small core set of colors from which all possible colors can be derived. The RGB model assumes that all colors are formed by a given combination of red, green, and blue; the CMYK model assumes that all colors are produced by a combination of cyan, magenta, yellow, and black. Both models fall short of describing the whole gamut of visible color. Also known as color system or color space. See CIE, gray scale, HSB/HLS.

color profile
A file containing data that describes a particular device's color space in relationship to an ideal, theoretical, device-independent color space (the CIE XYZ color space). Profiles facilitate the conversion of images from one color space to another and form the foundation of color management systems (CMS). Most profiles are generated using ICC standards.

color space
A three-dimensional geometric representation of the colors that can be discerned and/or created by a particular color model (the two expressions may be used interchangeably). May also refer to the range of possible colors that can be produced by a particular output device-such as a monitor, color printer, photographic film, or printing press-or the color description abilities of a particular file format; may also be known as a color gamut. Generally described by a color profile.

The reduction of file size to facilitate transmission or storage via any of various algorithms. Often required by image files, which are significantly larger than text files. Some algorithms allow the original data to be reconstituted upon decoding or decompression (lossless compression), while others discard data permanently (lossy compression), which allows a greater reduction in file size. Regardless of the type of compression used, the higher the level of compression, the more noticeable will be the loss in image detail. See codec.

continuous tone
Refers to images that have an unlimited (or nearly so) range of colors or shades of gray, and which show smooth gradation between shades. Digital image reproduction is always confined to limited palettes, albeit palettes that may have millions of different colors, while the ability of bitmapped images to mimic continuous tone is limited by their bit depth and resolution. See analog, HDRI, pixel.

controlled vocabulary
An established list of terms from which an indexer or cataloguer may select when assigning descriptors or subject headings to a record. See authority, cataloguing, indexing, thesaurus.

CRM (Conceptual Reference Model)
A metadata standard, developed by CIDOC, intended to provide a common and extensible semantic framework to which any cultural heritage information can be mapped.

Applications or data that can be used over more than one computer platform or operating system. Facilitated by the adoption of open standards.

A chart or table that represents the semantic mapping of fields or data elements in one metadata standard to fields or data elements in another standard that has a similar function or meaning. Crosswalks allow semantic interoperability. They enable heterogeneous databases to be searched simultaneously with a single query as if they were a single database, and facilitate accurate conversion from one metadata standard to another. Also known as field mapping or metadata mapping. See RDF.

DAM (Digital Asset Management)
A system that enables the management of digital objects, such as image files, from ingest to archiving and supports continued retrieval. Off-the-shelf DAM software may offer templates and other devices or strategies to facilitate ingest, metadata capture, and searching. May also be called media asset management (MAM).

A structured collection of data. The most common data-structuring model is "relational," where data is organized in related or linked tables that can be accessed or reassembled in many different ways. Object-oriented databases are also common.

data dictionary
An exhaustive list and description of data elements. May be contrasted with a metadata schema, which is a selection of data elements and rules for their use geared to a particular purpose.

DCMI (Dublin Core Metadata Initiative)
Body engaged in the development of interoperable online metadata standards to support a broad range of purposes. See Dublin Core.

See compression.

derivative file
A file derived or created from another file, rather than created during an original digitization process. Differs from a copy insofar as the derivative file may be altered in some way from the original.

derivative master
A high-quality "working" image file that is derived from an archival master image file, then subjected to some form of processing, such as color correction. May also be known as a submaster. Typically used as the source from which smaller, lower-quality access images intended for transmission over the Internet are derived, while archival masters are kept reserved.

Electronic technology that generates, stores, and transmits data in terms of a limited number of discrete states, most commonly as binary data in which two possible states, positive or nonpositive, are represented by 1 or 0, respectively. Because there are only two possible values, the accuracy of binary digital data at any given point is relatively easy to test, and therefore digital technology facilitates the creation of accurate copies. See digital image.

digital archaeology
The process of reclaiming digital information that has been damaged or is unusable due to format or media obsolescence. May employ any number of techniques. See digital preservation.

digital asset
See digital object.

digital camera
An image-capture device that directly captures digital images without the use of film or other analog processing. Digital cameras typically employ CCD photosensors and output bitmapped images. See drum scanner, flatbed scanner, transparency scanner.

digital certificate
An electronic identifier issued by a certification agency that establishes a user's credentials. Contains the registrant's name, a serial number, certificate expiration information, a copy of the certificate holder's public key, and the digital signature of the certificate-issuing authority. A recipient can verify that a certificate is real by comparing the public key received with that held in a registry for the certificate holder.

digital image
An image described as a set of digital data, such as pixels or vectors. Digital images may be digitized from analog sources such as photographs or may be generated directly within computer applications. If they are not born digital, bitmapped images consist of pixels whose values are derived from samples taken from analog originals, and may use thousands or millions of discrete gradations of color to approximate analog continuous tone images. See bitmap, vector graphic.

digital object
Data (the content or "essence" of a digital file) and the metadata describing it, regarded together as a single entity. Also known as a digital asset, an information object, or an information package. May also refer to born digital objects.

digital preservation
The specific problems and methods of preserving digital, as opposed to analog, assets because of their vulnerability to format obsolescence and media decay. Various strategies have been developed to respond to this, including documentation, the gathering of preservation metadata, the use of open standards, redundant storage, refreshing, migration, emulation, technology preservation, re-creation, and digital archaeology.

digital signature
A form of electronic authentication of a digital document. Digital signatures are created and verified using public-key encryption and serve to tie the document being signed to the signer.

The process of deriving digital objects from analog originals by converting their sampled values to binary code. Also known as analog-to-digital conversion and image capture.

DIN (Deutsches Institut für Normung)
National standards body that represents German interests at European and international levels.

Light-sensitive electronic components used in image capture. They function as one-way valves that sense the presence or absence of light and create a digital signal that the computer converts into pixel values.

directory (or directory service)
A listing of users and user passwords linked to information about which network resources each user may access. Examples include LDAP, Active Directory, and NDS.

DMZ (DeMilitarized Zone)
In the computer network context, a computer host or small network that provides an intermediate space between an extranet and an intranet and so prevents direct access to internal network resources by unauthorized users. Typically secured by two or more firewalls.

Textual information that describes a work of art or image, recording its physical characteristics and placing it in context. May be regarded as one of the most basic preservation strategies for digital files. See cataloguing, digital preservation, metadata.

domain name
An address that identifies an Internet or other network site and acts as a mnemonic alias for an IP address. Domain names consist of at least two parts: the top-level domain, which specifies host addresses at a national or broad sectoral level (e.g., ".edu" for the U.S. educational sector); and the subdomain, which is registered to a specific organization or individual within that domain (e.g., "getty" is registered to the Getty Trust within the .edu domain).

dot pitch
The distance between phosphor "dots," the smallest visual components of an electronic display device. Dot pitch is measured in millimeters (mm) and indicates how sharp a displayed image can be: the smaller the dot pitch, the sharper the image. Users working with images will usually want 0.28mm or finer dot pitch. See monitor resolution.

DRM (Digital Rights Management)
Server software that may use a number of techniques to control distribution of (usually commercial) content over the Web.

drum scanner
A high-quality image-capture device that uses PMT technology. The original is secured to the drum surface with mounting tape and oil, and the drum then revolves at several hundred revolutions per minute around the scanning mechanism, which in turn moves along the drum, executing a tight spiral scan of its entire surface. Capture resolution is determined by the number of samples per revolution and the speed at which the scanning sensor moves. Allows higher resolution, wider dynamic range, and greater bit depth than flatbed scanners. See digital camera, transparency scanner.

DTD (Document Type Definition)
A formal specification of the structural elements and markup definitions to be used in encoding SGML-compliant documents. Examples of DTDs include EAD and HTML. XML is a flexible format that allows for the creation of various DTDs to fit particular purposes. See XSD.

Dublin Core
A minimal set of metadata elements that creators or cataloguers can assign to information resources, regardless of the form of those resources, which can then be used for network resource discovery, especially on the World Wide Web.

DVD-ROM (Digital Versatile Disk, Read-Only Memory)
A type of write-once, read-many (WORM) disk used to store and distribute large amounts of digital data on low-cost, optically recorded media. The DVD-ROM is a newer, and more densely packed, form of storage than the CD-ROM, and therefore not as well established or, possibly, as reliable for archival purposes. A double-sided, dual layer disk can store up to seventeen gigabytes of data, but the more densely packed the data is, the more vulnerable it is likely to be to degradation. Gold-reflective-layer DVDs are recommended for long-term storage.

dynamic range
The ratio between the brightest and darkest parts of an image, or the potential range of color and luminosity values that can be represented within an image or produced or recognized by a particular output or capture device. See bit depth, color space, HDRI, palette.

EAD (Encoded Archival Description)
An SGML DTD that represents a highly structured way to create "finding aids" for groupings of archival or manuscript materials, making them accessible to researchers by listing the constituent items and their locations.

effective resolution
May be used misleadingly as a substitute term for interpolated resolution. Generally refers to "real" resolution under given circumstances. Examples include: the possible capture resolution of a digital camera, as constrained by the area actually exposed by the camera lens; the number of pixels per inch of an image, as affected by resizing that image; or the capture resolution of a scan taken from an intermediary such as a photograph, when mapped to the scale of the original object.

A digital preservation strategy that uses current software to simulate original or obsolete computer environments. May either restore full functionality to archival data or provide a simple viewing mechanism. See digital archaeology.

A way of transforming data into "cyphertext" through the use of computer algorithms that rearrange the data bits in digital signals in order to prevent them from being read by unauthorized users. May also be used for user and document authentication, because only designated users or recipients are given the capability to decrypt or decipher encrypted materials.

A private network that allows an organization to share information, such as parts of their intranet, with external users such as vendors or clients over the Internet. Extranet systems require security such as firewall server management and a means of user authentication.

A backup operational mode in which functions are assumed by secondary system components if the primary component becomes unavailable. Used to make storage and other systems more fault-tolerant.

film scanner
See transparency scanner.

Software, or software and hardware, that serves as a gateway to block certain types of network traffic, typically used to protect intranets from access through extranets. Most firewalls work by filtering packets and routing requests based upon IP addresses. Others use secure log-on procedures and authentication certificates.

flatbed scanner
An image-capture device resembling a photocopy machine. The object to be scanned is placed facedown on a glass plate, and a CCD array that passes beneath the glass captures an image of the object by sampling it at regular intervals. See digital camera, drum scanner, transparency scanner.

A specification for organizing data. Digital images (and their associated metadata) may be presented in a number of formats depending on compression schemes, intended use, or interoperability requirements. Some image formats are broadly decipherable, while others may only be accessible to certain application programs. See GIF, JPEG, JPEG2000, PNG, TIFF.

FTP (File Transfer Protocol)
A method of moving, transferring, or copying files between computers over the Internet via TCP/IP, rather than simply viewing them over the World Wide Web via HTTP with the aid of a Web browser.

GIF (Graphics Interchange Format)
A widespread digital image file format introduced by CompuServe, which supports basic animation capabilities and uses LZW compression. Can provide only 8-bit color (256 colors) and employs an adaptive palette for each image, making GIF undesirable for most continuous tone images, such as photographs, though useful for limited-palette, monochrome, or thumbnail images.

gray scale
The range of shades of gray that scanners and monitors can recognize and reproduce, or that is contained within a black-and-white image. May also be used as an alternative term for black and white (a black-and-white image that is digitized has been "grayscaled"). Or, a calibration target showing a standardized continuum of shades between black and white used to determine image-capture device specifications. See color chart.

A term used to describe a person who endeavors to break into a computer system for some purpose by circumventing security protocols. Sometimes used to describe a particularly talented programmer.

HDRI (High-Dynamic Range Image/Imaging)
An image or image processing device that utilizes a greater dynamic range or higher bit depth (generally 48-bit or higher) than can be shown on a typical display device, or that can be captured by a single exposure with an ordinary camera. The "extra" bits are used to record light and shade (luminance) more accurately.

In a computer file, a field or series of fields that precedes the main file content and contains metadata describing, for instance, the compression or size of an image. Some such fields are automatically filled, but additional metadata may be embedded into the header part of files of certain formats for description and management purposes.

HSB/HLS (Hue, Saturation, Brightness/Hue, Lightness, Saturation)
Two variations of a device-independent color model that closely matches the way the human eye perceives color. Often used in desktop graphics programs.

HTML (HyperText Markup Language)
An SGML-based markup language used to create documents for World Wide Web applications. Predominately concerned with specifying the design and appearance of content, rather than the representation of document structure and data elements. See XML.

ICC (International Color Consortium)
Body promoting the standardization of open, vendor-neutral, cross-platform color management system (CMS) architecture and components. Developer of the ICC color profile specification.

A system of letters and numbers used to classify the iconography of works of art, developed in the Netherlands.

IEC (International Electrotechnical Commission)
Organization that prepares and publishes international standards that may serve as a basis for national standardization for all electrical, electronic, and related technologies.

IEEE (Institute of Electrical and Electronics Engineers)
Body that promotes development and standards in the electronic and information technologies and sciences.

image capture
See digitizing.

image resolution
The number of pixels, in both height and width, making up an image. Generally, the higher the number of pixels, the greater the image's clarity and definition. See resolution.

See indexing.

The process of making a list of terms and other data stored in a structured data file and used to enhance access and discovery. Indexing terms represent the most salient information necessary to retrieve a record or object; they are often taken from a controlled vocabulary. See authority, cataloguing, thesaurus.

The process of entering new assets into a management system. The contributor transmits an asset and its metadata, either bundled together as a single digital object or separately, to allow accurate retrieval and eventual reuse of the asset.

Combining systems, applications, or sets of data so that they work together. In "seamless" integration, the distinctions or boundaries between systems are imperceptible to users.

A digital entity has integrity when it is whole and sound or when it is complete and uncorrupted in all its essential respects. See authenticity.

Allows users to communicate with, or use, applications by entering or requesting data. Most are now graphical user interfaces (GUIs), in which functions are displayed graphically and can be activated using a cursor or similar pointing device rather than using older text-, keyboard-, or menu-driven controls. Hardware interfaces allow pieces of equipment to communicate or work together.

A global collection of computer networks that exchange information by the TCP/IP suite of networking protocols.

The ability of different computer-based systems or applications to work together correctly, particularly in the correct interpretation of data semantics, or their ability to understand and, where appropriate, utilize each other's data. Applications and systems that adhere to known standards promote interoperability and remove reliance on a small group of suppliers.

interpolated resolution
The resolution at which a device is capable of capturing or generating an image using interpolation (i.e., using data that has no authentic relation to an original). See optical resolution.

An estimation of a value within two known values. A means by which a device can exceed its optical resolution capacity by inserting new pixels in between those derived by sampling the original. Can improve apparent picture quality; however, interpolated images tend to look blurred when they are enlarged and use data that is inauthentic or not derived from the original.

A private network that is accessed via TCP/IP and other Internet protocols but uses a gateway to limit access, typically to local users recognized by IP address, domain, or by some other means of authentication.

IP (Intellectual Property)
Any intangible asset that is a product of human knowledge and ideas. Examples include patents, copyrights, trademarks, and software. IP may also denote "Internet Protocol."

IP (Internet Protocol)
The method by which data packages are delivered from computer to computer over the Internet. Once delivered, the Transmission Control Protocol (TCP) puts them into the correct order. IP may also denote "intellectual property."

IP address
Part of the Internet Protocol (IP). A hierarchical, numeric addressing system that can be used to identify each device sending or receiving information on a network with a 32-bit number.

ISO (International Organization for Standardization)
Body that promotes standardization. Many national standards-making bodies, such as ANSI, participate in, and contribute to, ISO standards making. The Joint Photographers Experts Group (JPEG) and the Motion Picture Experts Group (MPEG) are both bodies within the ISO.

ITU (International Telecommunications Union)
Organization with the United Nations System that coordinates telecom networks and services. The ITU-T division produces standards or recommendations for all areas of telecommunication.

JFIF (JPEG File Interchange Format)
A public domain iteration of the JPEG image-compression format.

JPEG (Joint Photographers Experts Group)
A body within the ISO. Also a widely adopted image compression standard developed by that body, which uses a lossy-compression algorithm able to significantly reduce image file size while maintaining reasonable image quality. Typically capable of compression ratios from 10:1 to 20:1.

A file format that uses wavelet compression to allow both lossy and lossless compression and can provide scalable images from a single compressed file. Commercial implementations are becoming available, and open-source implementations are in development. A separate standard to JPEG, and generally able to provide reasonable image quality at higher compression ratios (some sources cite ratios of 2:1 with lossless compression and up to 200:1 with lossy compression).

JSP (Java Server PagesT)
One of several methods of dynamically generating Web pages in response to user input that may be used to gather information from remote databases. Platform-independent technology developed by Sun Microsystems that utilizes small programs called "servlets." See ASP, CGI, PHP.

LAN (Local Area Network)
A limited network, typically within a building or department and owned and operated by the user. May be connected to other networks, such as the Internet, via network points known as gateways. An ethernet is a high-bandwidth LAN specification used to network computers and other devices together in a cabled or wireless environment.

LCSH (Library of Congress Subject Headings)
A controlled vocabulary of terms commonly used to retrieve library materials.

lossless compression
Reduction in file size without loss of information, achieved by storing data more efficiently. A bitmapped image that has undergone lossless compression will be identical to the original uncompressed image when decompressed. The GIF, TIFF, PNG, and JPEG2000 image formats allow lossless compression, which cannot shrink file size to the extent possible with lossy compression.

lossy compression
Reduction in file size that involves permanent loss of information. Algorithms selectively discard data in order to attain a greater size diminishment than is possible with lossless compression. Entails a decrease in quality, but this is often imperceptible (or nearly so) with image files, depending on the level and type of compression employed. The JPEG and JPEG2000 formats allow lossy compression.

LZW (Lempel-Ziv-Welch)
A proprietary lossless-compression algorithm.

Data presented in an electromagnetic form that a computer can access, such as data stored on disk or tape, and organized in such a way that given the correct program, a computer can process or execute instructions contained in the data, such as rendering an image.

MAM (Media Asset Management)
A system for handling media assets through processes such as cataloguing, controlling access, managing circulation, tracking rights and publication history, and ensuring preservation, or software designed to perform all or some of these tasks. May also be called digital asset management (DAM).

MAN (Metropolitan Area Network)
A network that connects users over a region larger than a LAN but smaller than a WAN. Can be used to denote the interconnection of several LANs but most often applies to the interconnection of networks in a city into a single, larger network.

MARC (MAchine-Readable Cataloguing)
A set of standardized metadata structures that facilitates cooperative cataloguing and data exchange in information systems. Developed to describe bibliographic materials but extended to describe nonbibliographic holdings.

master file (or master image)
A high-quality, uncompressed digital file, or the highest quality file available, from which other files, most commonly smaller, compressed files for online access, can be derived. Master images will have the greatest level of detail and color fidelity available. See archival master, derivative master.

Commonly defined as "structured data about data," or data captured in specific categories or elements. Metadata can include data associated with either an information system or a data object or set of objects for purposes of description, administration, preservation, the documentation of legal requirements, technical functionality, use and usage, and so forth. See cataloguing, digital object.

metadata schema
A set of rules for recording or encoding information that supports a specific metadata element set.

meta tag
An HTML tag that enables descriptive metadata to be embedded invisibly on Web pages, used by some search engines to establish relevance to search requests.

METS (Metadata Encoding and Transmission Standard)
A flexible XML format for digital library objects that provides a "wrapper" to hold together the various types of metadata that may be used to describe an asset or group of assets. Data and metadata may be embedded within a METS document, or the document may point to external resources. The format's generalized framework offers a syntax for the transfer of digital objects between repositories that may be used within the OAIS model.

A computer program that mediates between two existing, separate computer programs.

Digital preservation strategy that involves transferring data from a format or standard that is in danger of becoming obsolete to a current format or standard. The most common example is the process of upgrading files to become compatible with a new version of software or operating system. May also be known as conversion or reformatting.

MIX (Metadata for Images in XML)
XML metadata schema developed by NISO and the Library of Congress, based on the NISO Data Dictionary: Technical Metadata for Digital Still Images.

MODS (Metadata Object Description Schema)
XML metadata schema developed by the Library of Congress and the MARC Standards Office designed to both transmit selected data from existing MARC 21 records and enable the creation of original resource description records.

monitor resolution
May be used interchangeably with screen resolution or may indicate the maximum possible resolution of a computer monitor. Higher monitor resolution indicates that a monitor is capable of displaying finer and sharper detail, or smaller pixels. Monitor detail capacity can also be indicated by dot pitch.

MPEG (Motion Picture Experts Group)
A body within the ISO that has produced standards for the compression, storage, and documentation of multimedia and motion pictures, such as the MPEG-7 standard or the MPEG-21 Multimedia Framework.

MPEG-7 (Multimedia Content Description Interface)
A metadata standard that provides a set of standardized tools to describe multimedia content. Both human users and automatic systems that process audiovisual information are within its scope.

NAF (Name Authority File)
Authority file maintained by the Library of Congress that contains headings for names, uniform titles, and series.

NAS (Network-Attached Storage)
A system where a data storage device is attached to a LAN and assigned its own IP address, rather than being attached to the server offering data processing and management functionality, thus releasing the server from data delivery duties. May be incorporated into a SAN system. Affordable consumer NAS systems are entering the market as of this writing.

Used to describe applications that are able to process XML data without transforming it to another format. For instance, native-XML databases allow XML documents to be stored, indexed, and retrieved in their original format, preserving their content, tags, attributes, entity references, and ordering. See XML-enabled.

Storage and retrieval system where assets are stored offline, such as on removable disks (hard drives, CD- or DVD-ROMs), but are available in a relatively short time frame if requested for online use or use over a network.

An arrangement of devices such as servers, computers, and printers joined by transmission paths by which programs make requests of one another. Local area networks (LAN), metropolitan area networks (MAN), wide area networks (WAN), and the Internet are all examples of networks.

network topology
A particular configuration used to connect devices on a network.

NISO (National Information Standards Organization)
Body that identifies, develops, maintains, and publishes technical standards to manage information in both traditional and new technologies.

Unwanted data or imperfections in a file that are somehow developed in the course of scanning, processing, or data transfer.

OAI (Open Archives Initiative)
Body that develops and promotes interoperability standards that aim to facilitate the efficient dissemination of content, such as its XML/Dublin Core-based Protocol for Metadata Harvesting, which provides a mechanism for "harvesting" or gathering XML-formatted metadata from diverse repositories.

OAIS (Open Archival Information System)
The Reference Model for an Open Archival Information System provides a common conceptual framework for creating archival systems designed to aid the long-term preservation of, and access to, digital information. Often cited in concert with METS; a METS document could serve as a Submission Information Package (SIP), an Archival Information Package (AIP), or a Dissemination Information Package (DIP) within the OAIS model.

Object ID
Metadata schema that sets out the minimum information needed to protect or recover an object from theft and illicit traffic. Its purpose is to uniquely identify an object in order to establish ownership.

Storage and retrieval system where assets are not immediately available for use, or not accessible through a network or computer, but stored on some independent media, such as a CD-ROM.

Storage and retrieval system where assets are immediately available for use or directly connected to a network or computer through fixed disk storage.

OPAC (Online Public Access Catalog)
Automated, computerized library catalogs made available to a wide range of users.

open architecture
A system design and framework that is well defined and uses open standards so that functionality can be added by third parties. This allows the original technology to benefit from industry-wide developments and allows users more flexibility in extending an application or building interoperability with other systems.

open source
A product or system whose workings or source code are exposed to the public and therefore to modification by anyone. Open source software is generally developed as a public collaboration and made freely available for use or modification as developers see fit, as opposed to proprietary products or systems. Open systems built to known standards promote interoperability.

open standards
Freely available structures, procedures, or tools for the uniform creation and description of data. Usually defined and perhaps maintained by a central body, but, unlike proprietary standards, users are not reliant on a private organization to license use and provide support.

optical resolution
The resolution at which a capture device, such as a scanner or digital camera, is capable of capturing pixel values based on actual samples taken from an original to construct an image. Optical resolution is the true measure of the capture capacity or quality of a scanner, as opposed to interpolated resolution.

output resolution
The resolution of an image based upon the dimensions, in pixels or units of length, as affected by the chosen output method, such as display on a monitor or printing on a page.

The set of colors that appears in a particular digital image, or the set of available colors based on the color space being used by a particular output device.

A character sequence providing means of authentication for a user requesting access to a computer or application. A password is typically entered along with a user name or identifier that, when paired with the password, serves to uniquely identify a user and associate the user with a particular profile, or set of access privileges and rights.

peer-to-peer (P2P)
As distinct from client/server relationship, a peer-to-peer network connects computers or programs so that no party is dedicated to serve the other, and any is able to initiate a transaction.

PHP (Hypertext Preprocessor)
One of several methods of dynamically generating Web pages in response to user input that may be used to gather information from remote databases. Utilizes open source script language. See ASP, CGI, JSP.

From picture element. The smallest programmed unit of a bitmapped image, similar to grain in a photograph or a dot in a halftone print. Pixel size, frequency, and color determine the accuracy with which photographic images can be represented. The greater a pixel's bit depth, the greater the number of different shades or colors it can represent. The larger or fewer the pixels within an image, the more likely "pixelation"-where individual pixels become apparent and break the illusion of continuous tone-is to occur. See resolution, sample.

An easily installed, usually downloadable program used by a Web browser to enable the use of certain media or the execution of specialized Web functionality. A media player, where audio or video encoding requires a particular player to decode and run media files, is an example of a plug-in.

PMT (PhotoMultiplier Tube)
An amplifying vacuum tube used in drum scanners. PMT technology is highly sensitive to differences in light intensity. It takes in light reflected from reflective originals or through transparent originals, converts it to an electrical signal, and amplifies the signal to measurable levels that can then be assigned digital color values.

PNG (Portable Network Graphics)
A patent-free file format for lossless compression of images that provides some additional features that improve the ability to control image appearance over the GIF format.

See digital preservation.

printer resolution
The maximum density of dots per inch that a printing device is capable of producing, or the density of dots per inch used in a particular printing.

A technology or product that is owned exclusively by a single commercial entity that keeps knowledge of its inner workings secret. Some proprietary products can only function when used with other products of the same ownership. The limitations of proprietary technology are fueling moves toward open standards.

public-key encryption
A security measure used in digital signatures wherein a value provided by a designated authority is combined with a private key value and used to encrypt transmitted data.

quality control
Techniques ensuring that accuracy and high quality are maintained through various stages of a process. For example, quality control during image capture might include comparing the scanned image to the original and then adjusting colors or orientation.

RAID (Redundant Array of Independent Disks)
Storage device comprised of systems of multiple hard disks holding the same information. Intended to increase performance and reliability in serving and storing data. There are various RAID configurations, each suited to different needs relating to demand or traffic, user needs such as read-only or read/write, and fault-tolerance requirements.

raster image
See bitmap.

RDF (Resource Description Framework)
A foundation for processing metadata that complements XML and includes a standard syntax for describing and querying data. Yet to be generally adopted as of this writing. A component of the proposed Semantic Web. See crosswalk.

A digital preservation concept postulating that if the delivery and content of born digital work such as multimedia or installation art could be adequately documented in a way that was independent of its native medium or platform, it would be possible to re-create it using a future medium or platform.

redundant storage
A digital preservation strategy whereby two or more copies of digital content are made on the same or different media and stored in different locations under archival environmental conditions. For example, one set of media may be stored offsite, or two institutions may agree to store one another's redundant copies.

A digital preservation strategy that protects against the possible degradation of digital content due to storage media decay by copying digital information held on a particular storage medium to a new medium, of the same or different type, while keeping the digital information itself in the same format.

refresh rate
The number of times that a screen display is refreshed or repainted per second, expressed in hertz. The refresh rate for each display depends on the system video card. Rates of below 70 Hz can cause image flickering and eyestrain, and, as such, rates of 75 Hz to 85 Hz are recommended.

May be used interchangeably with resizing. Alternatively, refers to changing the number and values of pixels in an image, technically by creating a new, empty bitmap of the desired dimensions and using the original image pixels as the basis from which to work out the values for each new pixel using various algorithms. Resampling generally involves interpolation and should be used cautiously. See compression.

May be used interchangeably with resampling. Alternatively, it refers to changing the physical dimensions of an image file without changing its pixel dimensions (for example, by changing the parameters for default print size). This would result in the output resolution of an image being set to a particular value but in no information (no pixels) being gained or lost.

A relative, rather than an absolute, value, usually expressed as the density of elements, such as pixels, within a specific distance, most commonly an inch. See capture resolution, effective resolution, image resolution, interpolated resolution, monitor resolution, optical resolution, output resolution, printer resolution, screen resolution.

resource sharing
The ability to federate collections of digital assets, or simply the metadata describing those assets, into larger resources where the costs of management are shared. Or, the ability to use assets and/or metadata outside the system or institution in which they originated. Examples include the OCLC (Online Computer Library Center, Inc.) Digital Archive; AMICO (the Art Museum Image Consortium), where contributors transmit catalog records, digital files, and metadata records for museum objects to a central repository; RLG (Research Libraries Group) Cultural Materials; and ARTstor.

RGB (Red, Green, Blue)
An additive color model or system for representing the color spectrum using combinations of red, green, and blue. Used in video display devices, and is the standard color system for most digital imaging devices and applications.

rights management
The description and identification of intellectual property (IP) and the rights and restrictions relating to it, including the conditions of use. May become very complicated where dealing with originals and various digital surrogates, where each instance of a work may have different restrictions placed upon it.

RLG Preservation Metadata Elements
A metadata element set intended to capture the minimum information needed to manage and maintain digital files over the long term. It captures technical rather than descriptive information and may be combined with any descriptive element set to describe an image file.

A digital value derived from measuring a discrete part of an analog original. See sampling.

sample depth
See bit depth, dynamic range.

The mechanism by which analog signals or objects are digitized. Sampling involves dividing an analog whole into regularly spaced, smaller discrete components, measuring the values of each such component, and converting these measurements to binary code. Provided enough samples are taken, the readings create the illusion of a continuous (i.e., analog) signal or object when decoded.

SAN (Storage Area Network)
A sophisticated online storage system where a high-speed special-purpose subnetwork of shared storage devices is accessible from any server in the LAN or WAN network of which the SAN is a part. In this system, data is readily accessible, but because it is stored separately from the server, server power and network capacity are released for other purposes. See NAS.

A scalable system is one whose size can be adjusted to meet ongoing requirements or where each part of a system is flexible enough to accommodate growth or reduction in another part. Open-source systems are more likely to be scalable over time, as they allow a greater number of alternative responses to change.

A device that captures images from analog sources for computer editing and display. See digital camera, drum scanner, flatbed scanner, transparency scanner.

screen resolution
Sometimes used interchangeably with monitor resolution. Otherwise refers to the number of pixels shown on a computer monitor screen. Screen or display resolution is variable and may be set to a number of default settings, such as 800 x 600 or 1024 x 768.

search engine
A set of programs accessed through the use of a Web browser that executes searches on the Internet. There are various search engines, but most include a program that goes out and reads searchable Web site pages, a program that creates an index or catalog of searched pages, and a program that receives the search request and returns results, usually in the form of a ranked list chosen from the index. May be confined to searching a particular site or set of sites.

Semantic Web
An idea or proposal to enhance the "intelligence" of the Web set forth by its inventor, Tim Berners-Lee. Web content authors would describe, catalogue, or index sites to improve the ability of future search engines to recognize context and therefore return more relevant results to Web users. See RDF, XML.

A computer program that provides services to other computer programs by responding to requests and supplying or accepting data. See client/server, storage.

SGML (Standard Generalized Markup Language)
ISO standard ISO/IEC 8879:1986, first used by the publishing industry, for defining, specifying, and creating digital documents that can be delivered, displayed, linked, and manipulated in a system-independent manner. See DTD, HTML, XML.

A broad range of data elements associated with transactions for museum objects developed by the UK-based mda.

SPIFF (Still Picture Interchange File Format)
A format intended to replace the ubiquitous, as of this writing, JFIF as the format for images using the JPEG compression algorithm. It offers additional color spaces as well as expanded functionality.

A single, default RGB color space for display devices, codeveloped by Microsoft and Hewlett-Packard, intended to standardize the many different RGB "flavors." May be used in conjunction with ICC color profiling.

Formal structures, procedures, and tools designed to promote uniformity and predictability. Typically developed, adopted, and promoted by large organizations that can advocate for their broad usage. Data standards enable the exchange of data, while technology standards enable the delivery of data between systems.

The physical holding of machine-readable data. Data may be stored on a variety of media, including hard disk, magnetic tape, and optical media such as CD-ROM. All data and media should be stored under archival environmental conditions (for instance, with temperature, lighting, and humidity controls) as a basic digital preservation strategy. See NAS, nearline, offline, online, redundant storage, SAN, storage networking.

storage networking
Various methods of storing data online while optimizing network performance. Generally involves the separation of data storage from server processing, allowing data to be directly transferred between storage devices and client machines and avoiding server bottlenecks. An Open Storage Network (OSN) is a storage networking system that emphasizes the use of standards to promote flexibility, interoperability, and scalability. Storage networking vendors have cooperated to form the Open Storage Networking Initiative (OSNI), and the term is often used in marketing. See NAS, SAN.

See derivative master.

Each red, green, and blue element in a pixel is referred to as a subpixel. Each carries a particular color channel.

TCP (Transmission Control Protocol)
The transport layer in the TCP/IP standard that provides reliable data delivery over the Internet. It divides files into numbered packets for sending and reassembles them in the correct order on delivery. It also detects corrupt or lost packets and resends them.

TCP/IP (Transmission Control Protocol/Internet Protocol)
The ISO standardized suite of network protocols that enables information systems to link to each other over the Internet, regardless of their computer platform. TCP and IP are software communication standards used to allow multiple computers to talk to each other in an error-free fashion.

technology preservation
A digital preservation strategy that involves preserving the complete technical environment, such as software, drivers, operating systems, fonts, passwords, and settings, necessary to facilitate access to archived data as well as its functionality, appearance, and behavior. An alternative approach is emulation.

TGM-I and TGM-II (Thesaurus for Graphic Materials I and II)
A body of terms maintained by the Library of Congress and used in subject indexing for pictorial materials such as prints, photographs, drawings, posters, architectural drawings, cartoons, and pictorial ephemera.

TGN (Getty Thesaurus of Geographic Names)
A controlled vocabulary maintained by the Getty Research Institute that lists and organizes alternative names for geographic locations.

A structured vocabulary of terms, typically including synonyms and/or hierarchical relationships, used to organize collections to allow cross-referencing for purposes of reference or retrieval. See authority, controlled vocabulary, cataloguing, indexing.

A proxy image, generally scaled to a much smaller size, used to represent a parent image in circumstances where loading the original is undesirable. Often used on the Web to display tables of smaller images with links to a larger view, preserving bandwidth and enabling the display of more images in the same area for the purposes of browsing.

TIFF (Tagged Image File Format)
A common image file format, TIFF is widely used as a format for storing uncompressed, or losslessly compressed, digital image data, though it also supports several compression algorithms. TIFF has gained wide acceptance for uses such as high-resolution scanning, image archiving, and editing applications.

transparency scanner
A scanner specifically designed to capture images from film or transparent media. See drum scanner, digital camera, flatbed scanner.

true-color image
Alternative term for 24-bit images.

ULAN (Union List of Artist Names)
A controlled vocabulary maintained by the Getty Research Institute that lists and organizes alternative names for artists.

vector graphic
An image composed of mathematically described elements, such as lines, arcs, and points (vectors), plotted in two- or three-dimensional space. The use of mathematical formulas to describe an image, instead of pixels, means vector graphics are not constrained by resolution, allowing them to be output at any size without loss of detail or other artifacts of pixel-based processing. Vector-based imaging is inappropriate for continuous tone imaging. See bitmap.

video card
The circuit board that enables a computer to display information on its screen. Determines the resolution, number of colors (bit depth), and refresh rate of display, in combination with the inherent limitations of the monitor used. Also known as a graphics adapter, display adapter, or video adapter.

VPN (Virtual Private Network)
A private data network that an organization can use to offer access to remote users or individuals, which makes use of public telecommunication infrastructure, such as the Internet, maintaining privacy through the use of a tunneling protocol and security procedures. Data is encrypted as it is sent and decrypted as it is received, so the virtual "tunnel" can only be traversed by properly encrypted data.

VRA Core Categories
A metadata schema specifically designed to describe not only original works but also their visual surrogates, including digital images, in considerable detail.

W3C (World Wide Web Consortium)
International consortium that develops vendor-neutral open standards and specifications for Internet and Web-based transactions, with the intent of promoting interoperability.

WAN (Wide Area Network)
A network that operates over a geographically dispersed area and is therefore typically slower than a LAN. WANs often link LANs together using a high-speed, long-distance connection.

A unique identifier added to a content file, such as an image, which can be visible or invisible to viewers. The mark, which could be a statement, symbol, or hidden encoding, is designed to persist through processing and serve as evidence of ownership in order to deter piracy.

wavelet compression
Compression technology, which may be lossy or lossless, that analyzes an image as a whole rather than dividing it into pixel blocks, as the JPEG compression algorithm does. This allows greater compression while still maintaining acceptable image quality. Wavelet technology can achieve compression ratios for color images of 20:1 to 300:1, and of 10:1 to 50:1 for gray scale images. See JPEG2000.

See World Wide Web.
Web browser
A client program installed on a user's computer that makes requests of a World Wide Web server using the Hypertext Transfer Protocol (HTTP). The most common Web browser programs currently in use are Netscape Navigator and Microsoft Internet Explorer.

Personal computers that run one of the Windows operating systems produced by Microsoft and an Intel microprocessor, such as the Pentium Pro. Also known as PCs. Generally contrasted with systems that use another operating system, especially Apple personal computers that use a Macintosh operating system and Motorola or PowerPC microprocessors.

World Wide Web
A vast, distributed client/server architecture for retrieving hypermedia or hypertext (interactive documents and media joined together by "links" or selectable connections) over the Internet using the Hypertext Transfer Protocol (HTTP).

A file used to encapsulate another file or collection of files. For example, the METS system either "contains" a digital file and its metadata in an XML file that describes them or points to files stored elsewhere.

XHTML (eXtensible HyperText Markup Language)
A reformulation of HTML as an application of XML designed to express Web pages. Users can extend XHTML to include new elements and attributes, and XHTML documents can be read and validated with standard XML tools.

XML (eXtensible Markup Language)
A simplified subset of SGML designed for use with the World Wide Web that provides for more sophisticated, meaningful (semantic), and flexible data structuring and validation than HTML. XML is widely forecast to be the successor to HTML as the language of the Web and is an essential component of the proposed Semantic Web. See XHTML, XSD, XSL, XSLT.

Designed to be compatible with XML. For instance, XML-enabled databases use middleware to translate between XML documents and traditional relational or object-relational databases. See native-XML.

XSD (XML Schema Definition)
A specification designed to express relational or non-narrative data in XML. Provides a standard way to validate data sets and to exchange them between applications. See database, DTD.

XSL (eXtensible Stylesheet Language)
The language used to create style sheets that describe how XML-structured data is to be displayed to Web users.

XSLT (eXtensible Stylesheet Language Transformations)
May be regarded as an extension of XSL. Provides a standard way to reorganize the data represented in one XML document into a new XML document with a different structure, or into another format altogether.

ISO 23950 and ANSI/NISO Z39.50 standard information retrieval protocol, a client/server-based method of searching and retrieving information from heterogeneous (usually remote) databases, most often used in bibliographic implementations. The ZNG (Z39.50 Next Generation) Initiative aims to update Z39.50 and make it compatible with XML and other current Web technologies.

The following sources were referred to in creating this glossary: Andy Moore's The Imaging Glossary, Electronic Document and Image Processing Terms, Acronyms and Concepts (1991); The Electronic Imaging Glossary (1994), compiled by Mimi King for the Library and Information Technology Association of the American Library Association; Internet.com's Webopedia; the FOLDOC Free On-Line Dictionary of Computing; and TechTarget's IT-specific encyclopedia Whatis?com. Maria Bonn, Nigel Kerr, and Jim Schlemmer contributed to the development of further definitions used in the first edition.