Big Sur: Glossary
This glossary defines terms used throughout the Big Sur draft.
As much as possible, we incorporate definitions from the
FGDC metadata standard or
EOSDIS glossary.
An EOSDIS glossary maintained by the EOS Project Science Office
is also available on-line at
http://spso.gsfc.nasa.gov/eos_glossary/EOS_Glossaryhd.html.
Section Coordinator:
Jean Anderson, jean_anderson@postgres.berkeley.edu
- access method
- An index strategy,
such as BTREE or RTREE, that speeds access to data.
- accuracy
- "The closeness of results of observations, computations or
estimates to the true values or the values accepted as being true."
[FGDC94]
- How good the measurement is.
See precision
and uncertainty.
- attribute
- A column in a table or class.
The attribute name is the column heading.
- "A defined characteristic of an entity type (e.g. composition)."
[FGDC94]
- AVHRR
- Advanced Very High Resolution Radiometer sensor on NOAA satellites.
- axis
- A dimension.
- band
- A layer in a satellite raster image.
A band may correspond to a
channel on the satellite,
or it may have been added from post-processing. For example,
the normalized difference vegetation index (NDVI)
is calculated from the first two bands in a AVHRR satellite image.
The Big Sur schema treats band,
channel, and layer
as synonyms.
- building block
- Base types and
tables in the Big Sur schema.
- channel
- A component of a satellite sensor that collects measurements in
a specific wavelength.
Some sensors call it a band.
The Big Sur schema treats band,
channel, and layer
as synonyms.
- class
- A group having the same or similar characteristics
[DARC88].
A table of objects composed of attributes.
For our purposes, a
POSTQUEL class is synonymous with a
SQL
table.
- DBA
- An acronym for
database administrator.
- data dictionary
- The description of each class, its associations, attributes, and
operations [RUMB91].
- database
- A grouping of related database objects.
An Illustra database is created with the micreatedb command and
a POSTGRES database with the createdb command.
- data set
- "A collection of related data."
[FGDC94]
- "A logically meaningful grouping or collection of similar or
related data."
[ECS94].
- dimension
- domain that can be expressed on a ratio scale.
- eastings
- Number of meters from the projection center; see
northings.
- database administrator
- The owner of a database.
- function
- A database object that executes one or more database operations.
Functions may be written in C or in the database query language
(SQL for Illustra and POSTQUEL for POSTGRES).
- geographic location
- "The spatial area of coverage by a granule, usually specified as
one of a fixed set of pre-determined regions, or "Global"."
[ECS94].
- geospatial data
- "Information that identifies the geographic location and characteristics
of natural or constructed features and boundaries on the earth.
This information may be derived from, among other things, remote sensing,
mapping, and surveying technologies."
[FGDC94]
- granule
- "The smallest aggregation of data that is independently managed
(i.e., described, inventoried, retrievable). Granules may be
managed as logical granules and/or physical granules."
[ECS94].
- grid
- "(1) a set of grid cells forming a regular, or nearly regular,
tessellation of a surface; (2) a set of points arrayed in a pattern that
forms a regular, or nearly regular, tesselation of a surface. The
tessellation is regular if formed by repeating the pattern of a regular
polygon, such as a square, equilateral triangle, or regular hexagon.
The tessellation is nearly regular if formed by repeating the pattern of
an "almost" regular polygon such as a rectangle, non-square parallelogram,
or non-equilateral triangle."
[FGDC94]
- grid cell
- "A two-dimensional object that represents the
smallest non-divisible element of a grid."
[FGDC94]
- grid coordinate system
- "a plane-rectangular coordinate system usually based on, and mathematically
adjusted to, a map projection so that geographic positions can be readily
transformed to and from plane coordinates."
[FGDC94]
- Illustra
- An object-relational database, the commercial version of POSTGRES.
Illustra-related web home pages include:
- index
- A database object that provides fast access to data by
keeping track of where data are stored, thus avoiding a scan of all
data in a table.
- inheritance
- Allows a table to use the attributes and methods from another table or
tables.
For example, many tables in the Big Sur schema inherit the
Description table, which was created like this:
CREATE TABLE Description
OF NEW TYPE Description_t
(
Abstract text,
Purpose text,
Supplemental text
);
Tables are inherited with the SQL under keyword.
The Big Sur Thesaurus table inherits Description:
CREATE TABLE Thesaurus
OF NEW TYPE Thesaurus_t
(
Keyword text,
Thesaurus_Code text
) UNDER Description;
The Thesaurus table ends up with these attributes:
Abstract
Purpose
Supplemental
Keyword
Thesaurus_Code
- instance
- Occurrence of an object (data); a record in a table.
- instrument
- From [ECS94]:
- A hardware system that collects scientific or operational data.
- Hardware-integrated collection of one or more sensors
contributing data of one type to an investigation.
- An integrated collection of hardware containing one or more
sensors and associated controls designed to produce data on/in an
observational environment.
- Landsat TM
- Thematic Mapper instrument on the Landsat satellite platform.
- layer
- "An integrated, areally distributed, set of spatial data usually
representing entity instances within one theme, or having one common
attribute or attribute value in an association of spatial objects.
In the context of raster data, a layer is specifically a two-dimensional
array of scaler values associated with all of part of a grid or image."
[FGDC94]
The Big Sur schema treats band,
channel, and layer
as synonyms.
- lineage
- How a data object, such as a satellite raster image or general
circulation model, was produced. Lineage includes the processing
history, algorithms and parameters that were used to produce the
object.
- map projection
- "the systematic representation of all or part of the surface of the
Earth on a plane or developable surface."
[FGDC94]
- metadata
- "Data about the content, quality, condition, and
other characteristics of data."
[FGDC94]
- "Information about data sets which is provided to the ECS by the
data supplier or the generating algorithm and which provides a
description of the content, format, and utility of the data set.
Metadata may be used to select data for a particular scientific
investigation." [ECS94].
- nadir
- The point directly beneath the satellite.
- northings
- Number of meters from the projection center; see
eastings.
- OID
- A unique identifier for an instance.
See object identifier .
- object
- A real-world thing or abstraction.
A satellite, AVHRR data, and a model are all objects.
A
table,
function,
index, and
rule are all database objects.
- object identifier
- A unique identifier, which never changes, for an instance.
- pixel
- "Two-dimensional picture element that is the smallest non-divisible
element of a digital image."
[FGDC94]
- platform
- "The EOS spacecraft and its subsystems without the instruments."
[ECS94].
- POSTGRES
- The extended-relational research database developed at U.C. Berkeley.
- POSTQUEL
- The POSTGRES query language.
- precision
- How good the instrument is.
See accuracy
and uncertainty.
- quality
- "An essential or distinguishing characteristic
necessary for cartographic data to be fit for use."
[FGDC94]
- query
- A database command.
- rule
- A database object that specifies an action to fire when a specific
condition occurs.
- SAR
- Synthetic Aperture Radar instrument/
- schema
- The overall logical organization of a database
[DARC88].
The structure or template of the data in a database
[RUMB91].
- The Big Sur schema consists of tables, which together we
refer to as building blocks.
- The SQL2 standard defines a schema to be a
partitioned namespace
[MELT93].
The Illustra create schema command creates such a
namespace and a single database may have many schemas.
- sensor
- "A device which transmits an output signal in response to a
physical input stimulus (such as radiance, sound, etc.). Science
and engineering sensors are distinguished according to the
stimuli to which they respond."
[ECS94].
- SQL
- The Structured Query Language, a database query language that was
adopted as an industry standard in 1986.
A major revision to the SQL standard was completed in 1992, called SQL2.
A good reference for SQL2 is
[MELT93].
A third revision, SQL3, is targeted for completion late in this
decade and will support some object-oriented features.
- system catalog
- A table that stores metadata about database objects.
For example, the users table (Illustra) and pg_user
class (POSTGRES) are a system catalog that stores information about
POSTGRES users like /etc/passwd stores information about UNIX users.
- table
- A grouping of attributes.
Tables store the base data in a database.
- time travel
- A capability that supports data versioning and historical queries.
- tuple
- A row of data in a table. Also called a record.
- type
- The data property of an attribute.
Databases provide built-in types such as integer, float, and text.
Illustra and POSTGRES provide complex built-in types, such as large_object,
and allow user-defined types. For example, the following create
statement creates the BigSurObject table:
CREATE TABLE BigSurObject
OF NEW TYPE BigSurObject_t
(
MetaData ref(MetaData_t) NOT NULL,
BigSurObject dlobh,
fileOffSet integer,
storageFormat text
);
It uses the builtin text and integer types as
well as a reference to the MetaData table. It also uses the
dlobh
user-defined type for the actual object.
- uncertainty
- Net effect of precision.
- view
- A virtual table. The definition is stored as
a query in a system catalog.
BigSur Introduction
Last Updated: $Date: 1994/12/17 21:29:40 $