Glossary

Version 1.0

The definitions in this Glossary follow the rules and guidelines for developing definitions contained in ISO 704 — Principles and methods of terinology

The terms and definitions in this Glossary apply to using and understanding the suite of all DDI standards and products.

Conventions:

  • Terms are written using lower case unless they are proper nouns in which case they are capitalized.

  • Context for usage of a term is indicated with angle brackets ('[',']').

  • Bold terms appearing in definitions and notes indicate those terms are defined elsewhere in the Glossary. 

  • Definitions are written with the principle of substitution in mind. The definition can replace the defined term in any place where it is used.

Glossary:

  • archive (n.)

    • collection of records, objects, metadata, or data intended for retention for as long as necessary

      • NOTE: Archives are typically managed based on established standards. Retention implies maintenance of the integrity, security, authenticity, and accessibility of the collection items according to policies established by the archive. DDI-Lifecycle supports various archive activities.

  • archive activity

    • activity that supports the future use of metadata and data through preservation, documentation, and access options.

      • NOTE: Archive activities can be done by anyone who manages the metadata and data during its lifetime and does not need to be done by a formal archive.

  • administrative metadata (n.)

    • content that is related to the interaction or use of the metadata within a specific system

  • category

    • concept used to group objects

      • the meaning of a category is based on the unifying characteristics of its group of objects

  • classification scheme

    • an organized set of categories defined within some scope

  • Codebook [standard] (n.)

    • see: DDI-Codebook

  • codebook [instance] (n.)

    • instance of a study description conforming to the DDI-Codebook standard

  • codebook (n.)

    • description of the methodology, questions, variables, codelists, and other aspects of a study and the data produced

  • codelist

    • list of code-category pairs, where a unique code represents each category

  • conceptual variable

    • description of the semantics of a variable independent of any particular representation or implementation

      • NOTE: A reusable, partial description of a variable limited to semantics. Semantics includes the meaning of values in the value domain, the characteristic represented, and all the associations between units and assigned values. Most general level in variable cascade. Used in DDI-Lifecycle, DDI-CDI, GSIM (Generic Statistical Information Model). Top level in variable cascade, with represented variable and instance variable.

  • controlled vocabulary

    • list of standardized terminology, words, or phrases used for indexing, content analysis, or information retrieval (CASRAI, CODATA)

      • NOTE: Usually in a defined information domain. For DDI, controlled vocabularies are standardized under the DDI Alliance. Other controlled vocabularies might not be formal standards, but are agreed upon in some context.

  • controlled vocabulary [DDI]

    • see DDI Controlled Vocabulary

  • correspondence

    • relationship that asserts a degree of similarity between two concepts

      • NOTE: The term crosswalk is sometimes used to refer to an individual correspondence.

  • correspondence table

    • synonym: crosswalk

    • set of correspondences between two distinct sets of concepts

      • NOTE: used to map similar things in collections. Concepts might be represented by terms in a vocabulary or classification system, fields in a database, entities, characteristics, or properties in a data model.

  • crosswalk

    • see correspondence table

      • NOTE: The term crosswalk is sometimes used to refer to an individual correspondence.

  • Data Documentation Initiative [product]

    • synonym: DDI

    • suite of open, human-readable, and machine-actionable specifications used internationally for describing the data produced with surveys and other observational methods in the social, behavioral, economic, and health science domains

  • Data Documentation Initiative [activity]

    • synonym: DDI

    • organized effort to produce metadata standards for the description of social, behavioral, and economic data to foster data reuse and interoperability.

      • NOTE: Started in 1995, following on work started in the 1980’s. Currently under the stewardship of the DDI Alliance.

  • data lifecycle

    • stages of the data production and management process to support research and policy covering conceptualization, design, acquisition, processing, analysis, sharing/dissemination, and archiving

      • NOTE: There are various models that emphasize different aspects of the lifecycle. For example Data Curation Centre (DCC). The DDI data lifecycle emphasizes aspects related to data production in the social, behavioral, economic, and health science domains.

  • datum

    • representation of a concept intended for information processing purposes

      • NOTE: typically an alphanumeric string; independent of subject area; used in DDI-CDI, defined as “a designation of a value.“ Commonly used as the most granular representation of information in a data processing or management system. A datum is described in DDI standards as a representation of dates, categories, numbers (quantities and percentages), and text.

  • DDI

    • see Data Documentation Initiative

  • DDI agency

    • registered entity responsible for assigning identifiers to DDI metadata items to ensure their uniqueness, and for the maintenance and versioning of those items

      • NOTE: May be a person, project, or organization which is intending to use DDI and registers to be assigned a recognized agency identifier, which is a prefix for all the DDI identifiers it assigns; the registration service is available at the https://ddialliance.org/products/ddi-agency-id-registry

  • DDI-CDI [acronym; standard] (n.)

  • DDI-Codebook [standard] (n.)

    • synonym: DDI-C

    • DDI standard defining a schema for a simple description of a study without the capability to link to descriptions of other studies

      • NOTE: Originally DTD-based, DDI-C is an XML Schema for validating XML serialization of DDI-Codebook standard. Supports discovery, preservation, and the informed use of data.  Defines descriptive content for variables, files, source material, and study level information. Includes metadata about a study; e.g. questionnaire, how the study was conducted.

      • NOTE: See https://ddialliance.org/Specification/DDI-Codebook/2.5/

  • DDI Controlled Vocabulary [technical product] (n.)

    • controlled vocabulary that can be used with DDI as well as for other purposes and applications

  • DDI DISCO [acronym; technical product] (n.)

  • DDI Instance [DDI-Lifecycle]

    • root element (<DDIInstance>) of a related set of DDI metadata as specified in the DDI-Lifecycle XML Schema

  • DDI instance [XML]

    • XML instance containing DDI metadata as specified in a DDI standard

      • NOTE: In non-XML syntax representations, the term “instance” may be used in a similar fashion, denoting the instantiation of a class, as in the DDI-CDI model.

  • DDI-Lifecycle

    • synonym: DDI-L

    • statistical metadata standard describing the data lifecycle as defined in the DDI-Lifecycle Model

      • NOTE: one of several standards from DDI Alliance.

  • DDI-Lifecycle Model [diagram]

    • depiction of the stages of the data lifecycle

      • NOTE: Version of the diagram from Inside View of DDI Version 3.0 (Thomas, Gregory and Piazza, 2005). This is informative; there is no formalization of this diagram in any DDI specification.

  • DDI-Lifecycle Model [information model]

    • specification of metadata used and reused throughout the data lifecycle

  • DDI Lite

    • subset of DDI-Codebook elements specifying basic information describing a dataset

  • DDI Profile [General]

  • DDI Profile [DDI-Lifecycle]

    • DDI Profile [General] of DDI-Lifecycle specification expressed as xml schemas

      • NOTE: defined in the DDI-Lifecycle specification in the element <DDIProfile>. As DDI-Lifecycle evolves, specifying profiles using other serialization schemes (e.g. RDF, JSON) is planned.

  • DDI scheme [DDI-Lifecycle]

    • package of related metadata items of a single type (e.g., concepts, variables, categories) for the purposes of data/metadata management and reuse, owned and maintained by a DDI agency

      • NOTE: defined in the DDI-Lifecycle specification. Analogous to a database table or a lookup list.

      • Examples: <RepresentedVariableScheme>, <QuestionScheme>, <ConceptScheme>, <CategoryScheme>.

  • DDI SDTL [technical product] (n.)

    • synonym: SDTL, Structured Data Transformation Language

    • language for representing data transformation commands

  • dimensional data

    • data organized as a matrix with each axis defined by a set of categories

      • NOTE: Synonyms: multidimensional data, data cube, N-Cube. The category sets define a coordinate system for identifying and describing individual datums, sometimes supplemented with time, or other non-categorical variables. Distinct from unit record data or sensor data.

      • Examples: Possible axes: Educational attainment level, age range, region, occupation, industry, and gender.

  • discovery (n.)

    • location and evaluation of available data or related/supplementary resources

      • NOTE: Enabled by search engines, catalogs, based on metadata such as that modeled using the DDI specifications that make resources discoverable (see ‘Findable’ part of FAIR).

  • dissemination

    • distribution of either data with related/supplementary resources or metadata for the purposes of use and reuse

  • DTD [acronym]

    • Document Type Definition

    • XML tagset definition for marking up a class of documents

      • NOTE: Document description language that predates XML schema. First version of DDI-Codebook was represented using a DTD. Note that term has been superseded by W3C XML schema for representing DDI work products. See DDI taxonomy page.

  • external reference [DDI specification]

    • link to a resource whose content is not represented inline in a DDI instance

      • NOTE: This is used when making reference to resources that complement the content of the metadata, e.g. a pdf copy of a questionnaire, or other DDI metadata intended for reuse that is published elsewhere.

  • FAIR [acronym] (adj.)

    • FAIR (Findable, Accessible, Interoperable, Reusable) Principles in the context of data publication or sharing.

      • NOTE: For details, see Wilkinson MD, Dumontier M, Aalbersberg IJJ, Appleton G, Axton M, Baak A et al. The FAIR Guiding Principles for scientific data management and stewardship. Scientific Data. 2016;3. 160018. https://doi.org/10.1038/sdata.2016.18

  • Genericode [OASIS]

  • identifiable [DDI-Lifecycle] (n.)

    • class of metadata objects that can be assigned an identifier

      • NOTE: used in DDI-Lifecycle, motivated by need to reference or reuse some information object.

  • IHSN [acronym]

    • International Household Survey Network; an informal network of organizations using DDI-Codebook

  • inline

    • represented explicitly in the XML instance

      • As opposed to included by reference to a separate resource. DDI-Lifecycle uses schemes to enable reuse of metadata, and these can be inline or external.

  • instance variable

    • description of a variable in the context of a particular dataset

      • Most granular element in variable cascade

  • instrument

  • interoperability

  • key-value data [data structure]

    • data structure consisting of ordered pairs comprising a key (identifier) and value (datum)

      • The structure is a set of ordered key-value pairs. The identifier is pointer to locate the value in the data structure. Values can be nested key-value structures. Typically the key is intended to encode or reference some semantics of the value. Within the context of a dataset, the key is considered unitary; key does not necessarily imply any internal structure within the key.

  • logical record [DDI-CDI, DDI-Lifecycle]

    • set of instance variables

      • Used in description of structure of a dataset. Does not specify format or specific implementation. The set is ordered in DDI-CDI, but not assumed or required to be an ordered set in DDI-Lifecycle.

  • long data

    • data structure in which each row contains a variable, its value, unit ID, and possibly some attribute values

      • Data structure consisting of separate records that associate an entity (unit) instance with one variable.

      • Like an event history; rows are variables. Allows adding new variables without adding columns. The values can be qualified with attributes that add information about observation method, time, etc. Can add rows to account for new variables.

  • machine-actionable data

    • structured data that are represented in a way so that a machine (computer) can be programmed to read and process each datum.

      • This is meant to be deterministic as opposed to probabilistic (e.g., natural language processing).

  • macrodata

    • data based on aggregates rather than individuals

      • compare with microdata

  • maintainable (n.)

  • measure (n.)

    • quantitative variable

      • NOTE: A numeric as opposed to a categorical variable.

  • metadata

    • data in the role of describing some object(s)

  • microdata

    • data that represent individuals from some unit type, universe, or population

      • compare with macrodata

  • multi-dimensional data

    • synonym: data cube, n-cube

    • data for which observations are logically organized by multiple facets (e.g. space, time, social determinants…) called dimensions that function as the axes of a coordinate system.

      • This is referred to as a data cube or n-cube in some communities. Tables can be understood as a presentation of an n-cube. Time is given special consideration in some communities as essential property of an observation. Some also use time as dimension.

  • observation

    • value for a variable for a particular unit

      • the result of an objective measurement process

  • physical record

    • stored representation of the values of a set of instance variables

      • how a logical record is implemented for storage in an information system. Instance of a physical record structure.

  • physical record structure

    • pattern according to which a set of instance variables are stored

      • mapping from logical record to physical record

  • population [DDI]

    • universe in which the individuals share time and geography

      • Typically the individuals are located in the same temporal and spatial extent. A pan-European survey administered in France and Greece might have a distinct population for each country.

      • NOTE: This term is defined as it is specifically used in DDI. See Demopaedia for the broader, commonly-used definition of the term.

  • question

    • a formal interrogative statement used to collect an observation

  • questionnaire

    • organized set of questions designed to collect information on specific topics from a respondent

  • register

    • authoritative list of items maintained for the purpose of documenting and promoting consistent usage

      • used as a source of administrative data for research on the relevant subjects, e.g., tax, births and deaths; typically secure and authoritative. A register is maintained by a registry.

  • registry

  • repository

    • place where items can be deposited for preservation and retrieval

      • A database of metadata and/or data intended to support search, discovery, and reuse

      • A database or file system are particular implementations of a repository.

  • represented variable

    • specification for the encoding of substantive values of a variable, based on a conceptual variable

      • Represented variable is middle level of the variable cascade. Includes substantive value domains. Reusable across all populations within the universe it describes.

  • resource package [DDI-Lifecycle]

    • reusable metadata outside the structure of a specific study or series

  • SDTL [acronym]

    • see DDI SDTL

  • sentinel value

    • value indicating missing, refused, or other invalid data result

      • Codes for representing sentinel values (missing, refused) are provided by each major statistical package, but differ between packages.

  • series [DDI]

    • collection of studies related for some purpose

      • for example using the same or similar questions and collecting the same or similar variables; includes longitudinal and repeat cross-sectional studies; similar to a statistical program in an official statistics context.

  • statistical classification

    • hierarchical classification scheme in which categories must be mutually exclusive and exhaustive at each level.

      • Subjects might include e.g. industries, occupations, diseases, education levels, etc.

      • Might be part of a group of classifications, maintained as a series of official versions. See usage in XKOS, DDI-CDI, DDI-Lifecycle, and GSIM. For example the North American Industrial Classification System (NAICS), International Classification of Diseases (ICD)

  • study [DDI] (n.)

    • organized activity and artifacts related to the design, collection, processing, and dissemination of data for the observation and analysis of a particular phenomenon

      • Used as an organizing principle for packages of data and metadata. May cover several related data files/datasets, surveys, methods, etc.

  • substantive value

    • subject matter-related value assigned by a variable for a unit that is useful for analysis or estimation

      • not processing-related (e.g. sentinel value)

  • survey (n.)

    • data collection activity based on a sample of some population used to estimate characteristics of that population

      • distinct from census or other studies based on an entire population

  • survey instrument

    • instrument based on a questionnaire

      • NOTE: specialization of instrument. DDI-Lifecycle includes a detailed model for survey instrument that is machine actionable.

  • time series

    • set of measurements based on the same measure made at different times

      • NOTE: Ideally all the measurements are comparable. Used as an important formalization with aggregates, where measures are multi-dimensional. A time series is the same in all dimensions except for time. The term is also used for observations in longitudinal and repeat cross-sectional contexts, where the observations are assumed to be comparable. Commonly the interval between measurements is regular.

  • unit

    • individual member of a group that is being measured

      • a distinct member of a universe. Technically, an individual whose properties correspond to the characteristics of a unit type. Properties distinguish units; characteristics distinguish unit types.

  • unit of measurement

    • consistent and agreed-upon scale for expressing, quantifying, and comparing values of a measure

      • NOTE: A quantity is used to define a measurement reference system. A quantity kind e.g. length, temperature, currency, has specific quantities for that kind, e.g. meter, degree Kelvin, Euro, respectively.

  • unit type [DDI]

    • class of units defined by essential characteristics

      • Examples: person, household, business establishment. A kind of entity based on a set of characteristics. The characteristics are specific to the study context. Ideally a category of individuals in a non-overlapping classification.

  • universe [DDI]

    • class of individuals that share a unit type and typically have other characteristics in common, exclusive of time and geography

      • Given a unit type, a universe is the domain of those ‘units’ that is observed. For example a unit type might be ‘humans’ and a universe might be ‘humans who are nurses’. A population is a universe at a given place and time. Some definitions of universe are more or less precise about the characteristics differentiating universe and population, e.g. DDI-Lifecycle and DDI-Codebook. The definition here is consistent with DDI-CDI.

      • NOTE: This term is defined as it is specifically used in DDI. See Demopaedia for the broader, commonly-used definition of the term.

  • URI [acronym]

    • Uniform Resource Identifier

    • compact sequence of characters that identifies an abstract or physical resource

      • defined in IETF RFC 3986. URL and URN are kinds of URI, see IETF RFC 3305. Each URI begins with a scheme name that refers to a specification for identifiers within that scheme (see IETF RFC 7595 ).

  • URN [acronym]

    • Uniform Resource Name

    • URI intended to serve as persistent, location-independent, resource identifier

      • DDI is in the process of registering a URN namespace and syntax for identification of resources that conform to the standards published by the Data Documentation Initiative (DDI) Alliance. The registration process and identifier syntax rules are described in IETF RFC 2141. Originally, the idea was that a URI would be either a URL or a URN. See discussion in IETF RFC 3305.

  • value [DDI] (n.)

    • concept represented by a datum.

      • NOTE: A datum is a representation of a value. A value is a concept underlying a datum.

  • value [computer science] (n.)

    • representation of some entity that can be manipulated by a computer program

      • Definition from Mitchell, 1996 (ISBN 0-262-13321-0). Discussion of ideas like ‘literal value', 'passing value by reference’ occur in DDI documentation, but use the computer science meaning of the term, rather than the DDI sense.

      • For reference, highlight differences between GSIM and DDI: ‘A Datum is the actual instance of data that was collected or derived. It is the value which populates a Data Point. A Datum is the value found in a cell of a table.’ (GSIM 1.2 definition, specified as synonym of value)

  • value domain

    • set of allowed values

      • DDI-CDI defines value domain as a ‘Set of permissible values for a variable (adapted from ISO/IEC 11179)'. DDI-Lifecycle uses value representation for this term.

  • variable

    • mapping to a value domain from a set of units corresponding to a single unit type.

      • A mapping is an association. The usage in DDI does not correspond exactly with other common uses (e.g. https://en.wikipedia.org/wiki/Variable_and_attribute_(research), http://en-ii.demopaedia.org/wiki/Variable), but is specific to data description. If the unit is a person, their gender would be characteristics. The values of these characteristics are also concepts, e.g. 'male'. The variable here is ‘gender’, the value ‘male’ is a category. Values that a variable assigns are properties of the units being measured.

  • variable [DDI-Lifecycle]

    • synonym of instance variable as used in DDI-CDI.

  • variable cascade [DDI-Lifecycle, DDI-CDI]

    • hierarchical description of a variable comprising conceptual, represented, and instance levels

      • key concept in DDI-Lifecycle, GSIM, and DDI-CDI. Cascade is designed to maximize reuse of metadata and facilitate data discovery and integration.

  • versionable (n.)

    • identifiable that can have individually distinguished versions

      • Allows evolving definition of usage, content, implementation of some information entity. Each version is an update based on the preceding version, defining a partial order.

  • wide data

    • data structure in which rows represent units and columns represent variables

      • Each row is a record representing a unit. Also referred to as a rectangular structure.

  • XKOS [acronym]

    • eXtended Knowledge Organization System.

    • extension of Simple Knowledge Organization System (SKOS) vocabulary that includes elements required to describe statistical classifications.

      • Adds semantics for relationships, levels in hierarchy, association of a concept with a hierarchy level. Adds more granular relations for broader/narrower. Also defines ordering relations (following/predecessor? transitive; next/previous not transitive…). Rendered in RDF. See https://rdf-vocabulary.ddialliance.org/xkos.html this is a DDI product. SKOS is a W3C product.