Basic data types

The NDA has only a few basic data types, with which all data management is defined:

Data field (field, f):

The basis of all data storage is data field, which corresponds to a data vector. The values in the vector must have the same data type, which can be integer, floating point number or character string.

Data frame (data, d):

Data frame can be used to store data in matrix form. It is a collection of data fields, which are required to have the same length, but can contain different data types. One data record is a selection of field values having the same row index.

Classified data frame (cldata, c):

Classified data frame can be used for data classification. This type of frame contains data fields of integers, but they can have different lengths. Each field in the frame corresponds to one class and the integer values in the fields are references to data records, which have been chosen to that class by some classifier. Normally, the integers are indexes referring to data records stored in some data frame.

Structures:

There are a few structural data items, which cannot be easily or efficiently converted into these three basic types. Thus, the system is able to store any data structures, but handling operations must be defined separately for them. Here are two typical examples of structures:

TS-SOM (som, s):

The structure of TS-SOM is one specific structure type implemented in the current version. However, note that the weights of the SOMs are not stored as a matrix. Instead, a separate data frame is used.

Graphics (gr):

Properties of the graphical presentations are stored in special structures.

Frames (data and classified data) actually contain references to fields. One field can be referred to by several frames, for instance, when the select (see section 2.9) command has been used. This should be taken into account when frames and fields are deleted. When a frame is deleted, typically all of its fields are also deleted, i.e., if they are not referred to by other frames. There are also operations to unlink fields from frames, and to delete a field including all the references from frames.

The order of fields has not been explicitly defined and cannot be easily changed. However, some operations suppose that fields are ordered. The operation select creates references to fields in the given order to the new frame. Correspondingly the listing operations show the fields in that order, in which they have been chosen or created.