# 3. Terms and definitions¶

## 3.1. Namespaces¶

In the XML encoding rules for ISO 19115-2:2009 (ISO 19139-2:2012), elements are prefaced by a namespace in order to provide additional context for each element (both on a machine and human-readable level), which are separated from the element name proper by a colon. However, because these namespaces are most-often three letter abbreviations (e.g., GMD, GCO), they essentially add human-unfriendly ‘jargon’ to the start of all terms.

For the purposes of this document, unless otherwise noted, all elements are in the GMD namespace (native to ISO 19115:2003 / ISO 19139:2007).

Values in ISO 19139:2007 / ISO 19139-2:2012 are also stored within elements with a namespace and XML encoding convention. For example, free text is enclosed within a gco:CharacterString element, and Booleans in a gco:Boolean element. Unless otherwise noted, all elements which directly contain values are in the GCO namespace.

Other namespaces used include GMI (from ISO 19115-2:2009 / ISO 19139-2:2012), GMX, GML, DWR (Darwin Core Record Set), DWC (Darwin Core), and DCTERMS (Dublin Core). We also add the MER (for MERIDIAN) namespace to store extensions to ISO 19139-2:2012, for example to store the newly added Darwin Core elements. These are prefaced before any elements or values where they are used.

## 3.2. Common terms¶

Class - A ‘container’ element, a class typically includes multiple elements within it, which form its ‘value’.

Codelist - A type of controlled vocabulary, a codelist has a limited set of values which can be selected for use as a value.

Controlled vocabulary - A ‘dictionary’ which lists or controls the valid values within an element, controlled vocabularies are used to ensure consistent terminology and reduce the number of possible ways of filling an element.

Element - Elements are the structured parts of a metadata record. They can be filled with values, or contain other elements (see ‘Class’ above).

Free text - Free text is a description for any ‘value’ which can be filled in using your keyboard, and is not selected from a small list of values (such as a codelist). Certain free text fields may employ pattern matching (e.g., via regular expressions) to ensure a specific format is used - for example, email addresses must contain an ‘@’ symbol.

Obligation - The rules for filling in an element. In this document, obligation is almost always written as “Single letter - Single character” (e.g., “M-R”, “O-1”, “C-1”). The first letter describes the conditionality, which describes whether the element is mandatory (M), optional (O), or conditional (C). Conditional indicates the element is required in some circumstances, but optional in others. The second character represents the multiplicity and is, in almost all cases, the number 1 or the letter R. The multiplicity describes how many times the element can be used in a single instance. 1 indicates the element can only be used once in a single instance, while R indicates it can be repeated any number of times in a single instance.

(Metadata) Profile - Metadata profiles adapt a specific metadata standard and/or schema for specific local needs. These adaptations may add or remove elements and modify obligations. The North America Profile of ISO 19115 and this document are metadata profiles.

(Metadata) Schema - Rules for implementing a metadata standard in a specific format or document language. Establishes syntax, semantics, and obligations necessary for general use. ISO 19139:2007, ISO 19139-2:2012, and Darwin Core in XML (2015) are metadata schema.

(Metadata) Standard - A high level document laying out the basic metadata needs for a particular general field or application. These documents generally list metadata elements and how they are grouped together in classes or a metadata record. ISO 19115:2003, ISO 19115-2:2009, and Darwin Core are metadata standards.

Value - things contained in elements. Values may be numbers, letters, or other complex structures - depending on the rules of the element.

## 3.3. Acronyms¶

AIS - Automatic identification system. Used worldwide for tracking large ocean vessels.

ANZLIC - Australia New Zealand Land Information Council. The acronym is far more commonly used than the full name.

ASCII - American Standard Code for Information Interchange. An early character encoding standard which remains in use. Succeeded by ISO 8859.

DOI - Digital object identifier. Assigned by a trusted source, DOIs are universally unique identifiers and ubiquitous in online publishing.

EPSG - European Petroleum Survey Group. Hosts a geodetic parameter registry which can be useful for identifying and referring to coordinate reference systems and transformations.

FTP - File transfer protocol. A less-recent but still common way to transfer large files and access files from servers.

GCO - Geographic common extensible markup language. Used in ISO 19139:2007 to store many values.

GMD - Geographic metadata extensible markup language. Used extensively in ISO 19139:2007 for elements from ISO 19115:2003.

GMI - Geographic metadata for imagery and gridded data markup language (ISO 19115-2). Used in ISO 19139-2:2012 for elements from ISO 19115-2:2009

GML - Geography markup language (ISO 19136). Used in ISO 19139:2007 for storing certain geographic boundaries.

GMX - Geographic Metadata XML schema.

HTTP(S) - Hypertext transfer protocol (Secure). The underlying markup language of the internet.

INSPIRE - Infrastructure for Spatial Information in the European Community.

ISBN - International Standard Book Number. An identifier for books. However, variations of a book (e.g., hardcover versus paperback) are assigned separate ISBNs.

ISO - International Organization for Standardization. Note that the name is not an acronym in any language - chosen to improve standardization.

ISSN - International Standard Serial Number. An identifier for serials such as journals.

MERIDIAN - Marine Environmental Research Infrastructure for Data Integration and Application Network.

MIME - Multipurpose Internet Mail Extensions. Used to describe different digital document formats in a standard way. For more details, refer to Mozilla’s list of MIME types.

SeaVoX - the combined SeaDataNet and MarineXML Vocabulary Content Governance Group, overseen by the British Oceanographic Data Centre.

URI - Uniform resource identifier. A generic way to specify how to access a file or resource.

URL - Uniform resource locator. One way resources can be retrieved online.

USIOOS - United States Integrated Ocean Observing System. A non-standard name for IOOS, used only to differentiate it from generic Integrated (or other words starting with I) Ocean Observing Systems.

UTC - Coordinated Universal Time. A time standard which specifies that time zones can be defined from their deviation from the central UTC time - UTC-0. UTC-O is sometimes used interchangeably with Greenwich Mean Time (GMT), which is an accurate analogy to within about a second.

UUID - Universally unique identifier. A more restrictive version of a simple identifier, a UUID has negligible probability of ever being assigned to multiple items.

WGS84 - World Geodetic System 1984. A coordinate system defined in 1984 by the United States National Geospatial-Intelligence Agency.

XML - Extensible markup language. A markup language used in a wide variety of situations with few underlying rules of its own.

## 3.4. How numbers are described¶

Boolean - A data type in which the only allowed values are a ‘True’ or ‘False’ condition. In ISO 19139:2007, to improve conformity and eliminate the many possible ways of writing these words (e.g., T, Tr, Y, Yes, True, Vrai, etc.), a single number (1 or 0) is used instead. 1 refers to a “true” condition, while 0 refers to a “false” condition. Type: gco:Boolean

Decimal - A real number without exponents. 300 is only represented as 300 - exponential notation (such as 3E2) is not allowed. Type: gco:Decimal

Integer - A whole number, with no decimal places. E.g., 121, 93192, 1. Type: gco:Integer

Measure - A combination of a real number and a unit of measure. Measure is a basic type which can be implemented as a distance, length, angle, scale… The real number records the number of those measures present. E.g., for recording ‘Number of oranges’ the number might be “3”, while the unit of measure might be “bushels”, “kilograms”, or “individual fruit”.

Non-negative - The number must not be less than 0 - that is, it cannot contain a negative sign as its leading character.

Positive - The number must be greater than zero. That is, it cannot contain a negative sign as its leading character, and it cannot be 0.

Real - Any (non-imaginary) number, including decimal places. E.g., 12.12923, 3.139, 92193.4. Note that large or small numbers can use power-of-ten exponential notation with capital E, so 300 could also be represented as 3E2, and 0.003 could be represented as 3E-3. Type: gco:Real

Set notation - Set notation for numbers can be useful to describe more complex value entry rules. A set of numbers appears like [a, b) - sometimes with the same brackets, and sometimes with different brackets. This set means “any number between a and b, including a, but not including b”. Square brackets denote inclusion, while rounded brackets indicate exclusion. Therefore, [0, 1] includes 0 and 1, but (0, 1) does not include 0 and 1 - but both include 0.24, 0.67, $$\frac{1}{\sqrt{2}}$$, etc.