A SAS data set is a
collection of data values and their associated descriptive information.
This collection is arranged and presented in a form that can be recognized
and processed by SAS. SAS data sets can be data files or views. A
SAS data file contains the following elements:
-
data values that are organized
into a rectangular structure of columns and rows
-
descriptor information that identifies
attributes of both the data set and the data values
A SAS view contains
the following elements:
-
instructions to build a table
-
descriptor information that identifies
attributes of both the data set and the data values
SAS data sets can be indexed by one or more variables,
known as key variables. A SAS index contains the data values of the
key variables that are paired with location identifiers for the observations
that contain the variables. The value and identifier pairs are ordered
in a B-tree structure that enables the engine to search by value.
SAS indexes are classified as simple or composite, according to the
number of key variables that they contain.
For more information
about SAS data sets, SAS files, SAS views, and SAS indexes, refer
to
SAS Language Reference: Concepts.
As a component of SAS,
SAS/GIS stores all of its data in SAS data sets. The
SAS/GIS spatial
database works as one logical entity, but is physically separated
into six different categories of data sets:
A given
SAS/GIS map
can reference only one chains, nodes, details, and label data set,
but it can reference multiple polygonal index and attribute data sets.
Multiple
SAS/GIS maps can use a single set of chains, nodes, and details
data sets.